If your OBD-II scanner displays P0198, your vehicle’s Engine Control Module (ECM) or Powertrain Control Module (PCM) has detected that the Engine Oil Temperature (EOT) Sensor circuit voltage is higher than the manufacturer’s expected operating range.
The generic OBD-II definition for P0198 is:
Engine Oil Temperature Sensor Circuit High Input
Unlike P0195, which indicates a general Engine Oil Temperature Sensor circuit malfunction, P0196, which indicates a range or performance problem, P0197, which indicates a low-input condition, or P0199, which indicates an intermittent signal, P0198 specifically means the PCM is receiving an abnormally high voltage signal from the Engine Oil Temperature Sensor circuit.
Modern engines rely on engine oil temperature data to control:
- Variable valve timing (VVT)
- Fuel injection
- Ignition timing
- Turbocharger protection
- Engine protection strategies
- Cooling system operation
- Emissions control
Common causes include:
- Failed Engine Oil Temperature Sensor
- Open circuit
- Broken signal wire
- Loose electrical connector
- Connector corrosion
- High circuit resistance
- Failed 5-volt reference circuit
- PCM software issues
- Failed PCM (rare)
Because the PCM interprets the high-voltage signal as extremely cold engine oil, it may alter fuel delivery, ignition timing, and engine warm-up strategies while illuminating the Check Engine Light.
What Does the P0198 Code Mean?
The PCM continuously monitors the Engine Oil Temperature Sensor by supplying a reference voltage and measuring the returning signal.
The Engine Oil Temperature Sensor helps the PCM manage:
- Fuel delivery
- Ignition timing
- Variable valve timing
- Turbocharger lubrication strategies
- Cooling fan operation
- Engine protection
- Emissions performance
If the PCM detects that the sensor voltage remains above the manufacturer’s calibrated maximum, it stores P0198.
Unlike P0196, which indicates implausible sensor performance, P0198 identifies a specific high-voltage electrical condition.
What Is the Engine Oil Temperature Sensor?
The Engine Oil Temperature (EOT) Sensor is a thermistor whose electrical resistance changes as oil temperature changes.
Depending on vehicle design, it may be mounted:
- In the oil pan
- In the engine block
- Near the oil filter housing
- Inside the oil cooler assembly
As engine oil warms, the sensor’s resistance changes and the voltage signal decreases accordingly.
The PCM converts this changing voltage into an accurate engine oil temperature reading.
Why Engine Oil Temperature Matters
Engine oil performs several critical jobs:
- Lubricates internal engine components
- Reduces friction
- Removes heat
- Protects bearings
- Supports turbocharger lubrication
- Operates hydraulic valve timing systems
Oil that remains too cold:
- Flows poorly
- Increases internal friction
- Reduces fuel economy
- Delays proper lubrication
Oil that becomes excessively hot:
- Loses viscosity
- Breaks down rapidly
- Reduces engine protection
- Accelerates internal wear
Accurate oil temperature information allows the PCM to balance engine performance, emissions, and reliability.
How the PCM Detects P0198
The PCM continuously monitors:
- Engine Oil Temperature Sensor voltage
- Reference voltage
- Ground integrity
- Sensor resistance
- Engine Coolant Temperature
- Intake Air Temperature
If the Engine Oil Temperature Sensor voltage remains higher than the allowable operating range, the PCM stores P0198.
Most manufacturers require the condition to occur during multiple monitoring events before illuminating the Check Engine Light.
What Does “High Input” Mean?
A High Input code means the PCM is receiving more voltage than expected from the Engine Oil Temperature Sensor circuit.
Possible causes include:
- Open circuit
- Broken signal wire
- Loose connector
- Failed Engine Oil Temperature Sensor
- High circuit resistance
- Failed reference voltage circuit
- PCM input fault
High voltage generally causes the PCM to interpret the engine oil as extremely cold, even if the engine has already reached operating temperature.
Can Wiring Problems Cause P0198?
Absolutely.
Electrical wiring problems are one of the leading causes of P0198.
Inspect for:
- Broken wiring
- Open circuits
- Loose connectors
- Corroded terminals
- Pinched wiring
- Damaged insulation
- High-resistance connections
An open signal circuit often causes the sensor voltage to remain near the full reference voltage.
Can the Engine Oil Temperature Sensor Fail?
Yes.
Engine Oil Temperature Sensors operate under:
- High engine temperatures
- Constant vibration
- Continuous oil exposure
- Frequent thermal cycling
Over time they may fail because of:
- Internal electronic failure
- Heat damage
- Oil contamination
- Moisture intrusion
- Aging
- Manufacturing defects
A failed sensor may continuously report extremely cold oil temperatures regardless of actual engine conditions.
Can Low Engine Oil Cause P0198?
Usually not.
Although low engine oil can affect actual oil temperature, it generally does not create a high-voltage sensor signal.
However, low oil may contribute to:
- Engine overheating
- Accelerated sensor wear
- Poor lubrication
- Increased engine stress
Always verify engine oil level and condition during diagnosis.
P0198 Quick Facts
| Item | Information |
|---|---|
| DTC | P0198 |
| Generic Definition | Engine Oil Temperature Sensor Circuit High Input |
| System | Engine Management |
| Severity | Moderate |
| Safe to Drive? | Yes, but repair soon |
| Common Symptoms | Check Engine Light, poor fuel economy, extended warm-up, reduced efficiency |
| Common Causes | Failed EOT sensor, open circuit, broken wiring, connector corrosion |
| Typical Repair Cost | $100–800+ |
| Related Codes | P0195, P0196, P0197, P0199 |
Common Vehicles That Experience P0198
P0198 commonly appears on:
- Ford
- Lincoln
- Chevrolet
- GMC
- Cadillac
- Dodge
- Ram
- Jeep
- Chrysler
- Toyota
- Lexus
- Nissan
- Infiniti
- Honda
- Acura
- Hyundai
- Kia
- Volkswagen
- Audi
- BMW
- Mercedes-Benz
The code is especially common on:
- Turbocharged engines
- Diesel engines
- Performance vehicles
- Heavy-duty trucks
- Vehicles equipped with engine oil coolers
What Does P0198 Really Mean?
The wording of P0198 often causes drivers to believe their engine oil is unusually cold.
The code does not automatically mean:
- The engine oil is actually cold.
- The engine has cooling problems.
- The thermostat has failed.
- The oil pump has failed.
- The PCM has failed.
Instead, it means the PCM has detected an Engine Oil Temperature Sensor circuit voltage that is higher than expected.
The underlying problem may involve:
- Engine Oil Temperature Sensor
- Signal wire
- Wiring harness
- Electrical connector
- Open circuit
- Reference voltage circuit
- PCM software
- PCM (rare)
Think of P0198 as the PCM saying:
“Your oil temperature sensor insists the engine oil is still ice cold. Unless you’ve somehow started your truck in Antarctica after an hour of driving, I’m guessing the sensor—or its wiring—is the one that’s confused.”
Common P0198 Scan Tool Patterns
Using a professional scan tool is one of the fastest ways to diagnose P0198.
Unlike P0195, which indicates a general Engine Oil Temperature (EOT) Sensor circuit malfunction, P0196, which indicates a range or performance problem, P0197, which indicates a low-voltage condition, or P0199, which indicates an intermittent signal, P0198 means the PCM is receiving an abnormally high voltage signal from the Engine Oil Temperature Sensor circuit.
Modern scan tools may display:
- Engine Oil Temperature (EOT)
- Engine Coolant Temperature (ECT)
- Intake Air Temperature (IAT)
- Ambient Air Temperature
- Battery Voltage
- Engine RPM
- Engine Load
- Freeze-frame data
Comparing Engine Oil Temperature with Engine Coolant Temperature is one of the quickest ways to determine whether the problem is electrical or mechanical.
Pattern 1: Engine Oil Temperature Reads Extremely Low
One of the most common scan-tool patterns is:
- Engine Oil Temperature remains extremely low
- Engine Coolant Temperature reaches normal operating temperature
- Oil temperature barely changes during driving
Possible causes include:
- Failed Engine Oil Temperature Sensor
- Open signal wire
- Loose electrical connector
- Broken wiring
- Internal sensor failure
An open circuit usually causes the PCM to interpret the engine oil as extremely cold.
Pattern 2: Engine Oil Temperature Is Much Lower Than Coolant Temperature
The scan tool may display:
- Engine Coolant Temperature reaches operating temperature
- Engine Oil Temperature remains far below normal
- Unrealistic temperature differences between sensors
Possible causes include:
- Faulty Engine Oil Temperature Sensor
- Open circuit
- High wiring resistance
- Connector corrosion
Oil temperature should gradually approach coolant temperature after warm-up.
Pattern 3: Engine Oil Temperature Remains Fixed
The scan tool may display:
- Constant low oil temperature
- No response to engine load
- No temperature increase during extended driving
Possible causes include:
- Failed Engine Oil Temperature Sensor
- Broken signal wire
- Open circuit
- PCM input circuit problem
A properly functioning sensor should respond continuously as engine oil warms.
Pattern 4: Rich Fuel Mixture During Warm-Up
Some vehicles may continue using cold-engine strategies because the PCM believes the oil has not warmed up.
Drivers may notice:
- Rich fuel mixtures
- Increased fuel consumption
- Extended warm-up enrichment
- Delayed closed-loop operation
These conditions are more noticeable during short trips.
Pattern 5: Multiple Temperature Sensor Codes
P0198 commonly appears together with:
- P0195
- P0196
- P0197
- P0199
- P0115
- P0116
- P0117
- P0118
Multiple temperature-related codes often indicate:
- Wiring damage
- Shared reference voltage issues
- Connector problems
- Sensor failures
Pattern 6: Poor Fuel Economy
Some vehicles may experience:
- Higher fuel consumption
- Delayed fuel trim adjustments
- Increased idle time
- Reduced engine efficiency
The PCM may continue using warm-up fuel strategies longer than necessary.
Pattern 7: Freeze-Frame Shows Fully Warm Engine With Extremely Cold Oil
Freeze-frame data may reveal:
- Normal Engine Coolant Temperature
- Long engine run time
- Fully warmed engine
- Extremely low Engine Oil Temperature
This pattern strongly suggests an electrical fault rather than an actual cold engine.
Common Symptoms of P0198
Symptoms vary depending on the vehicle and engine management strategy.
Common symptoms include:
- Check Engine Light
- Poor fuel economy
- Extended warm-up
- Rich fuel mixture
- Reduced engine efficiency
- Increased emissions
- Delayed closed-loop operation
- Failed emissions inspection
Many vehicles continue driving normally with few noticeable symptoms.
Check Engine Light
The Check Engine Light is usually the first symptom.
Most manufacturers require:
- Multiple failed monitoring events
- Confirmed high-voltage readings
- Stable operating conditions
before storing P0198.
Poor Fuel Economy
Drivers frequently report:
- Increased fuel consumption
- Reduced fuel efficiency
- Richer air/fuel mixtures
Incorrect oil temperature information may prevent the PCM from optimizing fuel delivery.
Extended Warm-Up Operation
When the PCM believes engine oil remains cold, it may:
- Delay ignition timing adjustments
- Maintain richer fuel mixtures
- Extend warm-up strategies
- Delay certain emissions functions
These strategies reduce efficiency once the engine is actually warm.
Increased Emissions
Improper Engine Oil Temperature data may contribute to:
- Higher hydrocarbon emissions
- Rich exhaust mixtures
- Reduced catalytic converter efficiency
Vehicles may fail emissions testing if the condition persists.
Is P0198 Serious?
P0198 is generally considered a moderate severity diagnostic trouble code.
Ignoring the problem may eventually result in:
- Poor fuel economy
- Increased emissions
- Reduced engine efficiency
- Improper engine management
- Long-term carbon buildup from rich operation
Prompt diagnosis is recommended.
Can You Drive With P0198?
Yes, in most cases you can continue driving for a short period, but repairs should not be delayed.
Driving may be acceptable if:
- Oil pressure is normal.
- Engine temperature remains normal.
- No overheating occurs.
- Performance remains acceptable.
Stop driving immediately if:
- Oil pressure warning light illuminates.
- Engine overheats.
- Engine begins knocking.
- Additional engine management warnings appear.
- Oil leaks are present.
P0198 vs Related Trouble Codes
Understanding related Engine Oil Temperature Sensor codes simplifies diagnosis.
P0198
Engine Oil Temperature Sensor Circuit High Input
The PCM detects sensor voltage above the expected operating range.
P0195
Engine Oil Temperature Sensor Circuit Malfunction
The PCM detects a general electrical circuit fault.
P0196
Engine Oil Temperature Sensor Range/Performance
The sensor communicates, but reported temperature is implausible.
P0197
Engine Oil Temperature Sensor Circuit Low Input
The PCM detects sensor voltage below specification.
P0199
Engine Oil Temperature Sensor Circuit Intermittent
The PCM detects unstable or intermittent sensor communication.
30 Common Causes of P0198
The most common causes include:
- Failed Engine Oil Temperature Sensor
- Open circuit
- Broken signal wire
- Loose electrical connector
- Connector corrosion
- High circuit resistance
- Damaged wiring
- Pinched wiring harness
- Melted wiring insulation
- Poor connector contact
- Bent connector terminals
- Moisture intrusion
- Heat-damaged wiring
- Rodent damage
- Failed 5-volt reference circuit
- Internal sensor failure
- Incorrect replacement sensor
- Previous wiring repairs
- Harness routing problems
- Charging system problems
- Electrical interference
- Oil contamination inside connector
- Corroded PCM connector
- Loose PCM connector
- Engine oil contamination
- Cooling system problems
- PCM software issue
- Failed PCM (rare)
- Manufacturing defect
- Internal PCM input circuit fault
Final Thoughts
The P0198 Engine Oil Temperature Sensor Circuit High Input code indicates the PCM has detected a sensor voltage higher than expected. In most cases, the root cause is a failed Engine Oil Temperature Sensor, open circuit, broken wiring, loose connector, connector corrosion, or high circuit resistance, rather than PCM failure.
Proper diagnosis should determine whether the fault originates in:
- Engine Oil Temperature Sensor
- Wiring harness
- Electrical connectors
- Signal wire
- Reference voltage circuit
- PCM connector
- Engine oil condition
- PCM software
- PCM
The next section of this guide covers:
- Complete diagnostic procedures
- Voltage testing
- Engine oil inspection
- Wiring diagnostics
- Repair procedures
- Repair costs
- Manufacturer-specific troubleshooting
Following a systematic diagnostic process prevents unnecessary parts replacement while restoring accurate engine oil temperature monitoring, proper engine protection, fuel economy, emissions compliance, and long-term reliability.
Related Pro Street Diagnostic Guides
- P0195 – Engine Oil Temperature Sensor Circuit Malfunction
- P0196 – Engine Oil Temperature Sensor Range/Performance
- P0197 – Engine Oil Temperature Sensor Circuit Low Input
- P0199 – Engine Oil Temperature Sensor Circuit Intermittent
- P0115 – Engine Coolant Temperature Sensor Circuit
- P0116 – Engine Coolant Temperature Sensor Range/Performance
How to Diagnose the P0198 Code
Diagnosing P0198 requires determining why the Engine Oil Temperature (EOT) Sensor circuit voltage is higher than the manufacturer’s specified operating range.
Unlike P0195, which indicates a general circuit malfunction, P0196, which indicates a range or performance problem, P0197, which indicates a low-voltage condition, or P0199, which indicates an intermittent signal, P0198 specifically means the PCM is receiving an abnormally high voltage signal from the Engine Oil Temperature Sensor circuit.
The underlying problem may involve:
- Failed Engine Oil Temperature Sensor
- Open circuit
- Broken signal wire
- Loose electrical connector
- Connector corrosion
- High circuit resistance
- Failed 5-volt reference circuit
- Cooling system issues
- PCM software
- Failed PCM (rare)
Proper diagnosis requires testing both the electrical circuit and the actual engine oil condition before replacing expensive components.
Safety Precautions
Before beginning diagnosis:
- Park on level ground.
- Apply the parking brake.
- Allow the engine to cool.
- Wear safety glasses.
- Wear protective gloves.
- Disconnect the battery before repairing wiring.
- Keep hot engine oil away from exposed skin.
Engine oil temperatures may exceed 250°F (121°C) after extended driving.
Tools Required
Professional diagnosis may require:
- Professional scan tool
- Digital multimeter
- Infrared thermometer
- Manufacturer wiring diagrams
- Back-probe pins
- Test light
- Basic hand tools
A scan tool capable of displaying Engine Oil Temperature (EOT) and Engine Coolant Temperature (ECT) simultaneously is highly recommended.
Step 1 – Verify the Code
Connect a professional scan tool.
Record:
- Stored DTCs
- Pending DTCs
- Permanent DTCs
- Freeze-frame data
Monitor:
- Engine Oil Temperature
- Engine Coolant Temperature
- Intake Air Temperature
- Battery voltage
- Engine RPM
Never erase diagnostic trouble codes before recording freeze-frame data.
Step 2 – Check for Related Trouble Codes
P0198 commonly appears with:
- P0195
- P0196
- P0197
- P0199
- P0115
- P0116
- P0117
- P0118
Related temperature sensor codes often simplify diagnosis.
| Code Combination | Likely Diagnosis |
|---|---|
| P0198 only | High-voltage Engine Oil Temperature Sensor fault |
| P0198 + P0195 | Circuit malfunction |
| P0198 + P0196 | Sensor performance issue |
| P0198 + P0197 | Wiring or sensor fault |
| P0198 + P0199 | Intermittent sensor problem |
| P0198 + P0116 | Cooling system correlation issue |
Repair obvious electrical faults before replacing the Engine Oil Temperature Sensor.
Step 3 – Review Freeze-Frame Data
Review:
- Engine RPM
- Vehicle speed
- Engine load
- Engine Oil Temperature
- Engine Coolant Temperature
- Intake Air Temperature
- Battery voltage
Freeze-frame data often reveals the operating conditions that caused the high-input fault.
Step 4 – Verify Engine Oil Level and Condition
Before electrical testing:
Inspect:
- Engine oil level
- Oil viscosity
- Oil condition
- Sludge buildup
- Oil contamination
Although poor oil condition typically does not create a high-voltage electrical fault, correcting maintenance issues helps eliminate secondary causes.
Step 5 – Inspect the Engine Oil Temperature Sensor
Locate the Engine Oil Temperature Sensor.
Inspect for:
- Physical damage
- Oil leaks
- Loose mounting
- Cracked housing
- Damaged connector
Replace any sensor showing obvious physical damage.
Step 6 – Inspect the Wiring Harness
Inspect the wiring between the Engine Oil Temperature Sensor and the PCM.
Look for:
- Broken wiring
- Chafed insulation
- Melted wiring
- Pinched harnesses
- Rodent damage
- Wiring contacting hot engine components
Open circuits are one of the most common causes of P0198.
Step 7 – Inspect the Electrical Connector
Disconnect the sensor connector.
Inspect for:
- Corrosion
- Bent terminals
- Loose connector pins
- Oil contamination
- Moisture intrusion
- Broken locking tabs
A loose connector can interrupt the sensor signal and create a high-voltage condition.
Step 8 – Verify Reference Voltage
Using a digital multimeter:
Measure:
- 5-volt reference
- Ignition voltage (if applicable)
Compare readings with manufacturer specifications.
If reference voltage is incorrect:
Inspect:
- Wiring harness
- Shared sensor circuits
- PCM reference voltage output
Step 9 – Verify Ground Integrity
Measure voltage drop across the sensor ground.
Inspect for:
- Loose grounds
- Corroded ground points
- High resistance
- Damaged wiring
Poor ground integrity may alter Engine Oil Temperature Sensor readings.
Step 10 – Measure Engine Oil Temperature Sensor Voltage
Reconnect the sensor.
Back-probe the signal wire.
Verify:
- Voltage with a cold engine
- Voltage at operating temperature
- Smooth voltage changes during warm-up
- Stable readings throughout engine operation
Voltage remaining consistently high typically indicates:
- Open circuit
- Broken signal wire
- Failed Engine Oil Temperature Sensor
- PCM input circuit fault
Step 11 – Compare Engine Oil Temperature With Coolant Temperature
After warm-up compare:
- Engine Oil Temperature (EOT)
- Engine Coolant Temperature (ECT)
Normally:
- Oil temperature gradually follows coolant temperature.
- Oil temperature may run slightly hotter under heavy load.
Large temperature differences often indicate:
- Sensor failure
- Wiring fault
- Cooling system issue
Step 12 – Verify Actual Oil Temperature
Use an infrared thermometer to measure:
- Oil pan temperature
- Oil filter housing
- Oil cooler (if equipped)
Compare actual temperature with scan-tool data.
If scan-tool temperature remains extremely low while measured temperature is normal:
Suspect:
- Engine Oil Temperature Sensor
- Open wiring
- PCM input circuit
Step 13 – Inspect the Cooling System
Verify:
- Coolant level
- Thermostat operation
- Cooling fan operation
- Radiator condition
- Water pump performance
Cooling system problems may influence actual engine oil temperature.
Step 14 – Review Technical Service Bulletins
Before replacing expensive components:
Review manufacturer Technical Service Bulletins (TSBs).
Look for:
- PCM software updates
- Engine Oil Temperature Sensor revisions
- Wiring harness improvements
- Cooling system updates
Some manufacturers have released software updates that reduce false P0198 detection.
Step 15 – Verify Charging System Voltage
Measure charging voltage.
Normal charging voltage:
13.5–14.8 volts
Charging system problems may affect sensor accuracy and reference voltage stability.
Step 16 – Inspect PCM Connector Pins
Inspect PCM connectors for:
- Corrosion
- Bent terminals
- Loose locking tabs
- Moisture intrusion
Poor PCM connections may interrupt sensor communication.
Step 17 – Perform a Wiggle Test
While monitoring Engine Oil Temperature:
Move:
- Wiring harness
- Sensor connector
- PCM connector
Watch for:
- Sudden temperature changes
- Signal interruptions
- Voltage fluctuations
Unexpected changes indicate wiring or connector problems.
Step 18 – Perform a Road Test
Drive the vehicle while monitoring:
- Engine Oil Temperature
- Engine Coolant Temperature
- Engine RPM
- Engine load
Verify that Engine Oil Temperature responds smoothly during:
- Cold starts
- Highway driving
- Heavy acceleration
- Extended idle
Step 19 – Verify Sensor Response
Observe how Engine Oil Temperature changes during:
- Cold start
- Warm-up
- Highway cruising
- Heavy engine load
- Cool-down
A properly functioning sensor should respond gradually without remaining fixed at unrealistically low temperatures.
Step 20 – Confirm the Diagnosis
Before replacing major components, verify:
- Engine Oil Temperature Sensor voltage
- Wiring continuity
- Connector condition
- 5-volt reference
- Ground integrity
- Engine oil level and condition
- Actual oil temperature
- Cooling system performance
- PCM software
Completing these diagnostic procedures prevents unnecessary parts replacement while accurately identifying the root cause of P0198.
Step 21 – Replace the Engine Oil Temperature Sensor
If testing confirms the Engine Oil Temperature (EOT) Sensor is producing a consistently high-voltage signal, replacement is the proper repair.
General replacement procedure:
- Allow the engine to cool completely.
- Disconnect the negative battery cable.
- Locate the Engine Oil Temperature Sensor.
- Disconnect the electrical connector.
- Remove the sensor using the proper socket.
- Inspect the sealing washer or O-ring.
- Install an OEM-quality replacement sensor.
- Torque the sensor to manufacturer specifications.
- Reconnect the electrical connector.
- Clear all diagnostic trouble codes.
- Verify proper Engine Oil Temperature operation using a professional scan tool.
Some manufacturers recommend updating PCM software after sensor replacement to improve temperature monitoring accuracy.
Step 22 – Repair Wiring Problems
Electrical wiring faults are among the most common causes of P0198.
Inspect and repair:
- Broken wiring
- Chafed insulation
- Melted wiring
- Pinched harnesses
- Rodent damage
- High-resistance circuits
Whenever possible:
- Replace damaged wiring sections
- Solder all repairs
- Protect repairs with adhesive-lined heat-shrink tubing
- Follow OEM wiring repair procedures
Poor-quality wiring repairs often result in recurring diagnostic trouble codes.
Step 23 – Repair Electrical Connectors
Inspect every connector between the Engine Oil Temperature Sensor and the PCM.
Repair:
- Corroded terminals
- Bent connector pins
- Loose terminal tension
- Oil contamination
- Moisture intrusion
- Broken locking tabs
- Damaged connector housings
Open or poorly connected terminals frequently create high-input sensor signals.
Step 24 – Repair Open-Circuit Faults
Because P0198 is a High Input code, inspect the circuit carefully for:
- Open signal wires
- Broken conductors
- Loose connector terminals
- High-resistance wiring
- Damaged splice connections
- Poor harness routing
Common failure areas include:
- Harnesses routed near exhaust components
- Areas exposed to engine vibration
- Previous wiring repairs
- Connectors contaminated with oil or corrosion
An open circuit often causes the PCM to receive nearly full reference voltage, triggering P0198.
Step 25 – Perform an Engine Oil Service
If the engine oil is:
- Dirty
- Contaminated
- Incorrect viscosity
- Overdue for replacement
Perform a complete oil and filter service using the manufacturer’s recommended oil specification.
Although poor oil condition rarely causes a high-voltage fault directly, fresh oil ensures accurate temperature readings and proper engine protection.
Step 26 – Repair Cooling System Problems
Inspect and repair:
- Thermostat
- Cooling fan
- Radiator
- Water pump
- Coolant leaks
- Low coolant level
Cooling system faults may alter actual oil temperature and should be corrected before final verification.
Step 27 – Inspect the Engine Oil Cooler
If equipped with an engine oil cooler, inspect:
- Oil cooler core
- Oil lines
- Coolant passages
- External leaks
- Internal restrictions
A malfunctioning oil cooler may affect engine oil temperature and contribute to inaccurate sensor interpretation.
Step 28 – Verify the 5-Volt Reference Circuit
If sensor voltage remains excessively high:
Inspect:
- 5-volt reference circuit
- Shared sensor reference circuits
- PCM voltage output
- Wiring continuity
An open reference circuit or broken signal wire may prevent the sensor from producing a valid temperature signal.
Repair all voltage supply problems before considering PCM replacement.
Step 29 – Update PCM Software
Before replacing expensive components:
Review manufacturer Technical Service Bulletins (TSBs).
Manufacturers occasionally release PCM updates correcting:
- False P0198 detection
- Engine Oil Temperature calculations
- Sensor calibration
- Engine warm-up logic
Always verify the PCM is running the latest available software.
Step 30 – Verify Proper System Operation
After repairs:
Monitor:
- Engine Oil Temperature
- Engine Coolant Temperature
- Intake Air Temperature
- Pending DTCs
Complete a full OBD-II drive cycle while monitoring live scan-tool data.
Engine Oil Temperature should rise steadily during warm-up and closely follow expected operating values without remaining unrealistically cold.
How to Fix P0198
The proper repair depends entirely on the diagnostic results.
Common repairs include:
- Replacing the Engine Oil Temperature Sensor
- Repairing broken wiring
- Repairing open circuits
- Cleaning or replacing electrical connectors
- Performing an engine oil and filter change
- Repairing cooling system problems
- Replacing a faulty thermostat
- Repairing the 5-volt reference circuit
- Updating PCM software
- Replacing the PCM (rare)
Verifying the Repair
After completing repairs:
- Clear all diagnostic trouble codes.
- Start the engine from a cold condition.
- Monitor Engine Oil Temperature using a scan tool.
- Compare Engine Oil Temperature with Engine Coolant Temperature throughout warm-up.
- Perform a complete road test.
- Complete an OBD-II drive cycle.
- Verify no pending or permanent DTCs return.
- Confirm realistic Engine Oil Temperature readings under idle, cruise, and heavy-load conditions.
A successful repair restores accurate oil temperature monitoring, proper engine management, fuel economy, emissions compliance, and long-term engine reliability.
Typical Repair Costs
| Repair | Typical Cost |
|---|---|
| Professional diagnosis | $100–250 |
| Engine Oil Temperature Sensor replacement | $150–400 |
| Wiring repair | $100–500 |
| Connector replacement | $75–250 |
| Engine oil and filter change | $50–150 |
| Thermostat replacement | $200–600 |
| Cooling system repair | $150–1,000+ |
| Oil cooler replacement | $300–1,200 |
| PCM software update | $100–250 |
| PCM replacement | $900–2,500+ |
Repair costs vary depending on vehicle design, labor rates, and engine configuration.
Common Diagnostic Mistakes
Avoid these common mistakes:
- Replacing the Engine Oil Temperature Sensor before checking for an open circuit
- Ignoring broken or partially disconnected wiring
- Failing to inspect connector terminals for corrosion
- Overlooking poor terminal tension
- Ignoring engine oil condition
- Clearing codes before recording freeze-frame data
- Ignoring Technical Service Bulletins
- Replacing the PCM before completing all electrical testing
Many P0198 repairs involve correcting open circuits or connector problems rather than replacing expensive components.
Manufacturer-Specific Notes
Ford/Lincoln
Inspect:
- Engine Oil Temperature Sensor wiring
- Engine harness routing
- Oil cooler
- PCM software
Power Stroke diesel and EcoBoost engines commonly develop wiring issues caused by engine heat.
General Motors (Chevrolet, GMC, Cadillac, Buick)
Verify:
- Engine Oil Temperature Sensor signal
- Oil cooler operation
- Cooling system performance
- Wiring continuity
Many GM engines compare Engine Oil Temperature with Engine Coolant Temperature for plausibility monitoring.
Chrysler, Dodge, Jeep, Ram
Inspect:
- Engine Oil Temperature Sensor
- Wiring harness
- Thermostat
- Connector condition
Broken wiring near the rear of the engine is a common failure point.
Toyota/Lexus
Inspect:
- Engine Oil Temperature Sensor
- Wiring continuity
- Cooling system
- Connector integrity
Electrical faults occur far more frequently than PCM failures.
Nissan/Infiniti
Verify:
- Engine Oil Temperature Sensor operation
- Harness continuity
- PCM software
- Engine oil condition
Turbocharged Nissan engines rely heavily on accurate oil temperature monitoring for engine protection.
Hyundai/Kia
Inspect:
- Engine Oil Temperature Sensor
- Wiring harness
- Ground circuits
- Cooling system
Sensor wiring failures remain significantly more common than PCM failures.
Frequently Asked Questions
What usually fixes P0198?
The most common repairs include replacing the Engine Oil Temperature Sensor, repairing broken wiring, repairing open circuits, cleaning or replacing electrical connectors, servicing the engine oil, repairing cooling system problems, repairing the 5-volt reference circuit, or updating PCM software.
Can I drive with P0198?
Yes, in most cases limited driving is possible if the engine is operating normally and oil pressure is within specification. However, repairs should be completed promptly because inaccurate oil temperature readings may reduce fuel economy and prevent proper engine management.
Does P0198 always mean the Engine Oil Temperature Sensor is bad?
No. Open circuits, broken wiring, loose connectors, connector corrosion, high circuit resistance, reference voltage problems, and PCM software issues can all trigger P0198 without a failed Engine Oil Temperature Sensor.
Can bad wiring trigger P0198?
Absolutely. Broken signal wires, open circuits, loose connectors, corroded terminals, damaged wiring harnesses, and poor electrical connections are among the most common causes of P0198.
Is P0198 a serious code?
P0198 is generally considered a moderate severity code. While it may not immediately damage the engine, incorrect oil temperature information can reduce fuel economy, increase emissions, delay normal engine operation, and interfere with engine protection strategies if left unresolved.
Final Thoughts
The P0198 Engine Oil Temperature Sensor Circuit High Input code indicates the PCM has detected a voltage signal higher than the manufacturer’s expected operating range. In most cases, the root cause is a failed Engine Oil Temperature Sensor, open circuit, broken wiring, loose connector, connector corrosion, or high circuit resistance, rather than PCM failure.
A complete diagnosis should always verify:
- Engine Oil Temperature Sensor voltage
- Wiring continuity
- Connector condition
- 5-volt reference
- Ground integrity
- Engine oil level and condition
- Cooling system performance
- Oil cooler operation
- PCM software level
Following a systematic diagnostic process prevents unnecessary parts replacement while restoring accurate oil temperature monitoring, proper engine protection, fuel economy, emissions compliance, and long-term reliability.
Continue Your Pro Street Temperature Sensor Series
Related guides include:
- P0195 – Engine Oil Temperature Sensor Circuit Malfunction
- P0196 – Engine Oil Temperature Sensor Range/Performance
- P0197 – Engine Oil Temperature Sensor Circuit Low Input
- P0199 – Engine Oil Temperature Sensor Circuit Intermittent
- P0115 – Engine Coolant Temperature Sensor Circuit
- P0116 – Engine Coolant Temperature Sensor Range/Performance
