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P0198 Code Explained: Engine Oil Temperature Sensor Circuit High Input Causes, Symptoms & Fixes

P0198 code illustration showing an Engine Oil Temperature Sensor with a high-voltage signal, open circuit wiring, Check Engine Light, Pro Street TV logo, and www.ProStreetOnline.com.

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:

Common causes include:

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:

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:

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:

Oil that remains too cold:

Oil that becomes excessively hot:

Accurate oil temperature information allows the PCM to balance engine performance, emissions, and reliability.

How the PCM Detects P0198

The PCM continuously monitors:

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:

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:

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:

Over time they may fail because of:

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:

Always verify engine oil level and condition during diagnosis.

P0198 Quick Facts

ItemInformation
DTCP0198
Generic DefinitionEngine Oil Temperature Sensor Circuit High Input
SystemEngine Management
SeverityModerate
Safe to Drive?Yes, but repair soon
Common SymptomsCheck Engine Light, poor fuel economy, extended warm-up, reduced efficiency
Common CausesFailed EOT sensor, open circuit, broken wiring, connector corrosion
Typical Repair Cost$100–800+
Related CodesP0195, P0196, P0197, P0199

Common Vehicles That Experience P0198

P0198 commonly appears on:

The code is especially common on:

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:

Instead, it means the PCM has detected an Engine Oil Temperature Sensor circuit voltage that is higher than expected.

The underlying problem may involve:

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:

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:

Possible causes include:

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:

Possible causes include:

Oil temperature should gradually approach coolant temperature after warm-up.

Pattern 3: Engine Oil Temperature Remains Fixed

The scan tool may display:

Possible causes include:

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:

These conditions are more noticeable during short trips.

Pattern 5: Multiple Temperature Sensor Codes

P0198 commonly appears together with:

Multiple temperature-related codes often indicate:

Pattern 6: Poor Fuel Economy

Some vehicles may experience:

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:

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:

Many vehicles continue driving normally with few noticeable symptoms.

Check Engine Light

The Check Engine Light is usually the first symptom.

Most manufacturers require:

before storing P0198.

Poor Fuel Economy

Drivers frequently report:

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:

These strategies reduce efficiency once the engine is actually warm.

Increased Emissions

Improper Engine Oil Temperature data may contribute to:

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:

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:

Stop driving immediately if:

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:

  1. Failed Engine Oil Temperature Sensor
  2. Open circuit
  3. Broken signal wire
  4. Loose electrical connector
  5. Connector corrosion
  6. High circuit resistance
  7. Damaged wiring
  8. Pinched wiring harness
  9. Melted wiring insulation
  10. Poor connector contact
  11. Bent connector terminals
  12. Moisture intrusion
  13. Heat-damaged wiring
  14. Rodent damage
  15. Failed 5-volt reference circuit
  16. Internal sensor failure
  17. Incorrect replacement sensor
  18. Previous wiring repairs
  19. Harness routing problems
  20. Charging system problems
  21. Electrical interference
  22. Oil contamination inside connector
  23. Corroded PCM connector
  24. Loose PCM connector
  25. Engine oil contamination
  26. Cooling system problems
  27. PCM software issue
  28. Failed PCM (rare)
  29. Manufacturing defect
  30. 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:

The next section of this guide covers:

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

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:

Proper diagnosis requires testing both the electrical circuit and the actual engine oil condition before replacing expensive components.

Safety Precautions

Before beginning diagnosis:

Engine oil temperatures may exceed 250°F (121°C) after extended driving.

Tools Required

Professional diagnosis may require:

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:

Monitor:

Never erase diagnostic trouble codes before recording freeze-frame data.

Step 2 – Check for Related Trouble Codes

P0198 commonly appears with:

Related temperature sensor codes often simplify diagnosis.

Code CombinationLikely Diagnosis
P0198 onlyHigh-voltage Engine Oil Temperature Sensor fault
P0198 + P0195Circuit malfunction
P0198 + P0196Sensor performance issue
P0198 + P0197Wiring or sensor fault
P0198 + P0199Intermittent sensor problem
P0198 + P0116Cooling system correlation issue

Repair obvious electrical faults before replacing the Engine Oil Temperature Sensor.

Step 3 – Review Freeze-Frame Data

Review:

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:

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:

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:

Open circuits are one of the most common causes of P0198.

Step 7 – Inspect the Electrical Connector

Disconnect the sensor connector.

Inspect for:

A loose connector can interrupt the sensor signal and create a high-voltage condition.

Step 8 – Verify Reference Voltage

Using a digital multimeter:

Measure:

Compare readings with manufacturer specifications.

If reference voltage is incorrect:

Inspect:

Step 9 – Verify Ground Integrity

Measure voltage drop across the sensor ground.

Inspect for:

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 remaining consistently high typically indicates:

Step 11 – Compare Engine Oil Temperature With Coolant Temperature

After warm-up compare:

Normally:

Large temperature differences often indicate:

Step 12 – Verify Actual Oil Temperature

Use an infrared thermometer to measure:

Compare actual temperature with scan-tool data.

If scan-tool temperature remains extremely low while measured temperature is normal:

Suspect:

Step 13 – Inspect the Cooling System

Verify:

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:

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:

Poor PCM connections may interrupt sensor communication.

Step 17 – Perform a Wiggle Test

While monitoring Engine Oil Temperature:

Move:

Watch for:

Unexpected changes indicate wiring or connector problems.

Step 18 – Perform a Road Test

Drive the vehicle while monitoring:

Verify that Engine Oil Temperature responds smoothly during:

Step 19 – Verify Sensor Response

Observe how Engine Oil Temperature changes during:

A properly functioning sensor should respond gradually without remaining fixed at unrealistically low temperatures.

Step 20 – Confirm the Diagnosis

Before replacing major components, verify:

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:

  1. Allow the engine to cool completely.
  2. Disconnect the negative battery cable.
  3. Locate the Engine Oil Temperature Sensor.
  4. Disconnect the electrical connector.
  5. Remove the sensor using the proper socket.
  6. Inspect the sealing washer or O-ring.
  7. Install an OEM-quality replacement sensor.
  8. Torque the sensor to manufacturer specifications.
  9. Reconnect the electrical connector.
  10. Clear all diagnostic trouble codes.
  11. 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:

Whenever possible:

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:

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:

Common failure areas include:

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:

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:

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:

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:

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:

Always verify the PCM is running the latest available software.

Step 30 – Verify Proper System Operation

After repairs:

Monitor:

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:

Verifying the Repair

After completing repairs:

  1. Clear all diagnostic trouble codes.
  2. Start the engine from a cold condition.
  3. Monitor Engine Oil Temperature using a scan tool.
  4. Compare Engine Oil Temperature with Engine Coolant Temperature throughout warm-up.
  5. Perform a complete road test.
  6. Complete an OBD-II drive cycle.
  7. Verify no pending or permanent DTCs return.
  8. 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

RepairTypical 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:

Many P0198 repairs involve correcting open circuits or connector problems rather than replacing expensive components.

Manufacturer-Specific Notes

Ford/Lincoln

Inspect:

Power Stroke diesel and EcoBoost engines commonly develop wiring issues caused by engine heat.

General Motors (Chevrolet, GMC, Cadillac, Buick)

Verify:

Many GM engines compare Engine Oil Temperature with Engine Coolant Temperature for plausibility monitoring.

Chrysler, Dodge, Jeep, Ram

Inspect:

Broken wiring near the rear of the engine is a common failure point.

Toyota/Lexus

Inspect:

Electrical faults occur far more frequently than PCM failures.

Nissan/Infiniti

Verify:

Turbocharged Nissan engines rely heavily on accurate oil temperature monitoring for engine protection.

Hyundai/Kia

Inspect:

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:

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:

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