If your OBD-II scanner displays P0187, your vehicle’s Engine Control Module (ECM) or Powertrain Control Module (PCM) has detected that the Fuel Temperature Sensor “B” circuit voltage is lower than the manufacturer’s expected operating range.
The generic OBD-II definition for P0187 is:
Fuel Temperature Sensor “B” Circuit Low Input
Unlike P0185, which indicates a general circuit malfunction, P0186, which indicates a sensor performance issue, P0188, which indicates a high-voltage condition, or P0189, which indicates intermittent communication, P0187 means the PCM is receiving an abnormally low voltage signal from Fuel Temperature Sensor “B”.
Many gasoline, diesel, and flex-fuel vehicles use multiple fuel temperature sensors to improve:
- Fuel delivery
- Injector pulse width
- Fuel density compensation
- Cold-start performance
- Emissions control
- Fuel system monitoring
Common causes include:
- Failed Fuel Temperature Sensor “B”
- Short-to-ground
- Damaged wiring
- Connector corrosion
- Poor electrical connections
- Low reference voltage
- Fuel Composition Sensor failure
- PCM software issues
- Failed PCM (rare)
A low-voltage signal prevents the PCM from accurately calculating fuel temperature, resulting in incorrect fuel delivery calculations and reduced engine efficiency.
What Does the P0187 Code Mean?
The PCM continuously monitors Fuel Temperature Sensor “B” to determine fuel temperature throughout the fuel system.
Fuel temperature affects:
- Fuel density
- Injector pulse width
- Fuel trim calculations
- Cold-start enrichment
- Fuel pressure strategies
- Emissions performance
If the PCM detects the sensor voltage has dropped below the expected operating range, it stores P0187.
Unlike a performance-related code, P0187 identifies a low electrical input signal rather than inaccurate sensor calculations.
What Is Fuel Temperature Sensor “B”?
Fuel Temperature Sensor “B” is an electronic thermistor whose resistance changes as fuel temperature changes.
Depending on vehicle design, it may be located:
- Inside the Fuel Composition Sensor assembly
- Along the fuel supply line
- In the fuel rail
- Near the high-pressure fuel pump
- Inside the fuel tank module
Vehicles equipped with multiple Fuel Temperature Sensors use Sensor “B” to monitor a separate portion of the fuel system from Sensor “A.”
The PCM uses this information to optimize:
- Fuel delivery
- Engine efficiency
- Fuel density compensation
- Cold-start operation
- Emissions control
Why Fuel Temperature Matters
Fuel density changes as temperature changes.
Cold fuel:
- Is denser
- Contains more energy per unit volume
- Requires shorter injector pulse widths
Hot fuel:
- Expands
- Becomes less dense
- Requires longer injector pulse widths
Accurate fuel temperature data allows the PCM to precisely adjust fuel delivery under all operating conditions.
How the PCM Detects P0187
The PCM continuously monitors:
- Sensor voltage
- Circuit continuity
- Reference voltage
- Ground integrity
- Signal stability
If Fuel Temperature Sensor “B” voltage falls below the manufacturer’s minimum threshold, the PCM stores P0187.
Most manufacturers require the fault to occur during multiple monitoring cycles before illuminating the Check Engine Light.
What Does “Low Input” Mean?
A Low Input code means the PCM is receiving less voltage than expected from Fuel Temperature Sensor “B”.
Possible causes include:
- Short-to-ground
- Failed sensor
- Low reference voltage
- Excessive wiring resistance
- Connector corrosion
- Internal sensor failure
Unlike P0185, which identifies a general electrical fault, P0187 specifically identifies insufficient signal voltage.
Can Wiring Problems Cause P0187?
Absolutely.
Electrical wiring problems are among the most common causes of P0187.
Inspect for:
- Short-to-ground
- Broken wiring
- Chafed insulation
- Corroded connectors
- Loose terminals
- Damaged wiring harnesses
Even minor wiring damage can significantly reduce sensor voltage.
Can Fuel Temperature Sensor “B” Fail?
Yes.
Fuel Temperature Sensors gradually wear over time.
Common causes include:
- Internal thermistor failure
- Heat cycling
- Fuel contamination
- Moisture intrusion
- Vibration
- Age
Many sensors begin producing weak voltage signals before failing completely.
Can Low Reference Voltage Cause P0187?
Yes.
Fuel Temperature Sensor “B” depends on a stable reference voltage supplied by the PCM.
Low reference voltage may result from:
- Wiring damage
- Connector corrosion
- PCM driver faults
- Excessive circuit resistance
Always verify reference voltage before replacing the sensor.
P0187 Quick Facts
| Item | Information |
|---|---|
| DTC | P0187 |
| Generic Definition | Fuel Temperature Sensor “B” Circuit Low Input |
| System | Fuel & Air Management |
| Severity | Moderate |
| Safe to Drive? | Usually, but repairs should not be delayed |
| Common Symptoms | Check Engine Light, poor fuel economy, hesitation, hard starting |
| Common Causes | Failed sensor, short-to-ground, damaged wiring, low reference voltage |
| Typical Repair Cost | $100–900+ |
| Related Codes | P0185, P0186, P0188, P0189 |
Common Vehicles That Experience P0187
P0187 commonly appears on:
- Chevrolet
- GMC
- Ford
- Lincoln
- Dodge
- Ram
- Jeep
- Chrysler
- Toyota
- Lexus
- Nissan
- Hyundai
- Kia
- Volkswagen
- Audi
The code is most commonly found on vehicles equipped with advanced flex-fuel systems or multiple fuel temperature sensors.
What Does P0187 Really Mean?
The wording of P0187 often causes drivers to assume Fuel Temperature Sensor “B” has completely failed.
The code does not automatically mean:
- The sensor must be replaced.
- The fuel pump has failed.
- The fuel is too cold.
- The PCM has failed.
- The engine has mechanical damage.
Instead, it means the PCM has detected a voltage signal from Fuel Temperature Sensor “B” that is lower than expected.
The underlying problem may involve:
- Fuel Temperature Sensor “B”
- Wiring harness
- Electrical connectors
- Ground circuit
- Reference voltage
- Fuel Composition Sensor
- PCM software
- PCM (rare)
Think of P0187 as the PCM saying:
“The voltage signal from Fuel Temperature Sensor ‘B’ is too low for me to accurately calculate fuel temperature.”
Common P0187 Scan Tool Patterns
Using a professional scan tool is one of the fastest ways to diagnose P0187.
Unlike P0185, which indicates a general circuit malfunction, P0186, which indicates a performance problem, P0188, which indicates a high-voltage condition, or P0189, which indicates intermittent communication, P0187 means the PCM is receiving a voltage signal from Fuel Temperature Sensor “B” that is lower than the manufacturer’s expected operating range.
Modern scan tools may display:
- Fuel Temperature Sensor “B”
- Fuel Temperature Sensor “A” (if equipped)
- Engine coolant temperature
- Intake air temperature
- Ambient air temperature
- Battery voltage
- Fuel trims
- Freeze-frame data
Comparing these values often helps determine whether the problem originates with the sensor, wiring, reference voltage, or PCM.
Pattern 1: Fuel Temperature Reading Is Extremely Low
One of the most common scan-tool patterns is:
- Fuel temperature far below normal
- Unrealistically cold readings
- Sudden drop in temperature
- Temperature inconsistent with engine operation
Possible causes include:
- Failed Fuel Temperature Sensor “B”
- Short-to-ground
- Low reference voltage
- Damaged wiring
The PCM interprets the low voltage as an abnormally low fuel temperature.
Pattern 2: Fuel Temperature Never Changes
The scan tool may display:
- One constant temperature
- Frozen fuel temperature
- No response as the engine warms
Possible causes include:
- Internal sensor failure
- Wiring fault
- Connector corrosion
- Low reference voltage
A sensor that never changes typically indicates an electrical problem rather than actual fuel temperature.
Pattern 3: Fuel Temperature Sensor “B” Is Much Lower Than Sensor “A”
On vehicles equipped with multiple sensors:
- Sensor “A” reports realistic temperatures.
- Sensor “B” reports values far lower than expected.
Possible causes include:
- Failed Fuel Temperature Sensor “B”
- Short-to-ground
- Connector damage
- Wiring resistance
Comparing both sensors is often one of the quickest ways to isolate the fault.
Pattern 4: Fuel Temperature Does Not Match Other Engine Sensors
The PCM compares Fuel Temperature Sensor “B” with:
- Engine Coolant Temperature (ECT)
- Intake Air Temperature (IAT)
- Ambient Air Temperature
If Fuel Temperature Sensor “B” consistently reports values that are significantly lower than expected, P0187 may be stored.
Pattern 5: Multiple Fuel Temperature Codes
P0187 commonly appears together with:
- P0185
- P0186
- P0188
- P0189
Multiple Fuel Temperature Sensor “B” codes often indicate:
- Sensor failure
- Wiring damage
- Fuel Composition Sensor failure
- Electrical circuit problems
Pattern 6: Fuel Trim Changes
Although P0187 is not a fuel trim code, incorrect fuel temperature calculations may affect:
- Short-Term Fuel Trim (STFT)
- Long-Term Fuel Trim (LTFT)
- Injector pulse width
- Cold-start enrichment
Fuel trims may change as the PCM compensates for incorrect fuel density calculations.
Pattern 7: Low Reference Voltage
Monitor reference voltage using a scan tool and digital multimeter.
Possible observations include:
- Reduced sensor voltage
- Low 5-volt reference
- Voltage drop under load
- Poor ground integrity
These conditions commonly trigger P0187.
Common Symptoms of P0187
Symptoms vary depending on how low the sensor voltage becomes.
Common symptoms include:
- Check Engine Light
- Poor fuel economy
- Hard starting
- Rough idle
- Hesitation
- Reduced acceleration
- Increased fuel consumption
- Failed emissions inspection
Some vehicles initially exhibit only the Check Engine Light.
Check Engine Light
The Check Engine Light is usually the first symptom.
Most manufacturers require:
- Multiple failed monitoring events
- Stable operating conditions
- Confirmed low sensor voltage
before storing P0187.
Hard Starting
Incorrect fuel temperature information may result in:
- Long crank times
- Rough cold starts
- Difficult hot restarts
- Occasional stalling
Cold-weather operation may make these symptoms more noticeable.
Reduced Fuel Economy
Incorrect fuel density calculations may cause:
- Rich fuel mixtures
- Increased fuel consumption
- Reduced adaptive fuel control
Fuel economy often declines gradually.
Hesitation During Acceleration
Improper fuel calculations may produce:
- Hesitation
- Delayed throttle response
- Flat spots
- Reduced engine performance
Performance issues are generally mild unless additional fuel system faults are present.
Rough Idle
Incorrect Fuel Temperature Sensor “B” readings may result in:
- Rough idle
- Engine vibration
- Idle instability
- Occasional stumbling
Idle quality usually improves once the sensor fault is corrected.
Is P0187 Serious?
P0187 is generally considered a moderate severity diagnostic trouble code.
Ignoring the problem may eventually result in:
- Reduced fuel economy
- Increased emissions
- Hard starting
- Poor drivability
- Inaccurate fuel delivery calculations
Although the vehicle usually remains drivable, repairs should not be delayed.
Can You Drive With P0187?
Usually, yes—but repairs should be completed as soon as practical.
Driving is generally safe if:
- The engine runs normally.
- No severe drivability concerns exist.
- The Check Engine Light is not flashing.
Stop driving immediately if:
- The engine repeatedly stalls.
- Severe hesitation develops.
- Fuel leaks are present.
- Multiple fuel system or misfire codes appear.
Most vehicles continue operating using default fuel calculations until repairs are completed.
P0187 vs Related Trouble Codes
Understanding related Fuel Temperature Sensor “B” codes simplifies diagnosis.
P0187
Fuel Temperature Sensor “B” Circuit Low Input
The PCM detects sensor voltage below specification.
P0185
Fuel Temperature Sensor “B” Circuit Malfunction
The PCM detects a general electrical circuit fault.
P0186
Fuel Temperature Sensor “B” Circuit Range/Performance
The sensor communicates, but its readings are outside expected operating limits.
P0188
Fuel Temperature Sensor “B” Circuit High Input
The PCM detects sensor voltage above specification.
P0189
Fuel Temperature Sensor “B” Circuit Intermittent
The PCM detects unstable or intermittent communication.
30 Common Causes of P0187
The most common causes include:
- Failed Fuel Temperature Sensor “B”
- Short-to-ground
- Low reference voltage
- Damaged wiring
- Broken wiring harness
- High circuit resistance
- Connector corrosion
- Loose electrical connectors
- Poor ground connection
- Moisture intrusion
- Heat-damaged wiring
- Rodent damage
- Fuel Composition Sensor failure
- Internal thermistor failure
- Fuel contamination
- Weak battery
- Charging system faults
- Connector pin damage
- Corroded ground point
- Improper aftermarket wiring repairs
- Harness routing problems
- Electrical interference
- Manufacturing defect
- PCM software issue
- Failed PCM (rare)
- Fuel pump module wiring damage
- Low system voltage
- Water intrusion into connectors
- Incorrect replacement sensor
- Excessive voltage drop in the circuit
Final Thoughts
The P0187 Fuel Temperature Sensor “B” Circuit Low Input code indicates the PCM has detected a voltage signal below the expected operating range from Fuel Temperature Sensor “B”. In most cases, the root cause is a failing sensor, short-to-ground, damaged wiring, connector corrosion, poor electrical connections, or low reference voltage, rather than PCM failure.
Proper diagnosis should determine whether the fault originates in:
- Fuel Temperature Sensor “B”
- Wiring harness
- Electrical connectors
- Ground circuit
- Reference voltage
- Fuel Composition Sensor
- PCM software
- PCM
The next section of this guide covers:
- Complete diagnostic procedures
- Sensor voltage testing
- Resistance testing
- Wiring inspection
- Repair procedures
- Repair costs
- Manufacturer-specific troubleshooting
Following a systematic diagnostic process prevents unnecessary parts replacement while restoring accurate fuel temperature monitoring, proper fuel delivery, improved fuel economy, and emissions compliance.
Related Pro Street Diagnostic Guides
- P0185 – Fuel Temperature Sensor “B” Circuit Malfunction
- P0186 – Fuel Temperature Sensor “B” Circuit Range/Performance
- P0188 – Fuel Temperature Sensor “B” Circuit High Input
- P0189 – Fuel Temperature Sensor “B” Circuit Intermittent
- P0182 – Fuel Temperature Sensor “A” Circuit Low Input
- P0183 – Fuel Temperature Sensor “A” Circuit High Input
How to Diagnose the P0187 Code
Diagnosing P0187 requires determining why Fuel Temperature Sensor “B” is producing a voltage signal below the manufacturer’s expected operating range.
Unlike P0185, which indicates a general circuit malfunction, P0186, which indicates a performance problem, P0188, which indicates a high-voltage condition, or P0189, which indicates intermittent communication, P0187 specifically means the PCM is receiving an abnormally low voltage signal from Fuel Temperature Sensor “B”.
The underlying problem may involve:
- Failed Fuel Temperature Sensor “B”
- Short-to-ground
- Low reference voltage
- Damaged wiring
- Connector corrosion
- Poor electrical connections
- Fuel Composition Sensor failure
- PCM software
- Failed PCM (rare)
Proper diagnosis requires testing the entire Fuel Temperature Sensor “B” circuit, not simply replacing the sensor.
Safety Precautions
Before beginning diagnosis:
- Park the vehicle on level ground.
- Apply the parking brake.
- Wear safety glasses.
- Work in a well-ventilated area.
- Disconnect the battery before repairing electrical wiring.
- Keep sparks and open flames away from the fuel system.
Always follow the manufacturer’s service procedures before disconnecting fuel system components.
Tools Required
Professional diagnosis may require:
- Professional scan tool
- Digital multimeter
- Oscilloscope (recommended)
- Infrared thermometer
- Manufacturer wiring diagrams
- Back-probe pins
- Test light
- Basic hand tools
A digital multimeter is essential for checking sensor voltage, resistance, continuity, and reference voltage.
Step 1 – Verify the Code
Connect a professional scan tool.
Record:
- Stored DTCs
- Pending DTCs
- Permanent DTCs
- Freeze-frame data
Monitor:
- Fuel Temperature Sensor “B”
- Fuel Temperature Sensor “A” (if equipped)
- Battery voltage
- Engine coolant temperature
- Intake air temperature
Always save freeze-frame information before clearing any diagnostic trouble codes.
Step 2 – Check for Related Trouble Codes
P0187 commonly appears with:
- P0185
- P0186
- P0188
- P0189
Related codes often simplify diagnosis.
| Code Combination | Likely Diagnosis |
|---|---|
| P0187 only | Low input fault |
| P0187 + P0185 | General circuit malfunction |
| P0187 + P0186 | Sensor performance issue |
| P0187 + P0188 | Voltage instability |
| P0187 + P0189 | Intermittent wiring fault |
Repair any additional electrical faults before replacing components.
Step 3 – Review Freeze-Frame Data
Review:
- Engine RPM
- Vehicle speed
- Fuel temperature
- Battery voltage
- Engine coolant temperature
- Intake air temperature
- Engine load
Freeze-frame data often identifies the conditions present when the low-input fault occurred.
Step 4 – Locate Fuel Temperature Sensor “B”
Depending on vehicle design, Sensor “B” may be located:
- Inside the Fuel Composition Sensor
- Along the fuel supply line
- In the fuel rail
- Near the high-pressure fuel pump
- Inside the fuel tank module
Consult the factory service manual before removing any components.
Step 5 – Inspect Fuel Temperature Sensor “B”
Inspect the sensor for:
- Physical damage
- Cracked housing
- Fuel contamination
- Loose mounting
- Heat damage
Visible damage may indicate the sensor requires replacement.
Step 6 – Inspect the Wiring Harness
Inspect the wiring between Fuel Temperature Sensor “B” and the PCM.
Look for:
- Chafed insulation
- Broken wiring
- Pinched harnesses
- Melted insulation
- Rodent damage
- Areas rubbing against metal components
Short-to-ground conditions are one of the most common causes of P0187.
Step 7 – Inspect the Electrical Connector
Disconnect the sensor connector.
Inspect for:
- Corrosion
- Bent terminals
- Loose connector pins
- Moisture intrusion
- Fuel contamination
Poor terminal contact often lowers sensor voltage.
Step 8 – Verify Reference Voltage
Using a digital multimeter:
Measure:
- Reference voltage
- Ignition voltage (if applicable)
Compare readings with manufacturer specifications.
Low reference voltage may indicate wiring or PCM problems.
Step 9 – Verify Ground Integrity
Measure voltage drop across the sensor ground.
Inspect for:
- High resistance
- Loose grounds
- Corroded ground points
- Damaged wiring
A poor ground can significantly reduce sensor voltage.
Step 10 – Measure Sensor Resistance
Most Fuel Temperature Sensors use a thermistor.
Disconnect the sensor.
Measure resistance using a digital multimeter.
Compare readings with manufacturer specifications at the current fuel temperature.
Readings outside specification typically indicate sensor failure.
Step 11 – Measure Sensor Voltage
Reconnect the sensor.
Back-probe the signal wire.
Monitor voltage while the engine reaches operating temperature.
Verify:
- Stable voltage
- Proper voltage changes
- Smooth signal transitions
Voltage consistently below specification confirms a low-input condition.
Step 12 – Check for Short-to-Ground
Disconnect the sensor.
Using a multimeter:
Check continuity between:
- Signal wire
- Chassis ground
Continuity where none should exist indicates a short-to-ground.
Repair wiring before replacing components.
Step 13 – Compare Actual Fuel Temperature
Use an infrared thermometer to measure:
- Fuel line temperature
- Fuel rail temperature (when accessible)
Compare actual temperatures with scan-tool readings.
Large differences suggest:
- Failed Fuel Temperature Sensor “B”
- Fuel Composition Sensor problems
- Wiring faults
- Electrical circuit issues
Step 14 – Review Technical Service Bulletins
Before replacing expensive components:
Review manufacturer Technical Service Bulletins (TSBs).
Look for:
- PCM software updates
- Sensor revisions
- Wiring harness improvements
- Fuel Composition Sensor updates
Some manufacturers have released updates addressing false P0187 detection.
Step 15 – Verify Charging System Voltage
Measure charging voltage.
Normal charging voltage:
13.5–14.8 volts
Low system voltage can affect sensor reference voltage and PCM calculations.
Step 16 – Inspect PCM Connector Pins
Inspect PCM connectors for:
- Corrosion
- Bent terminals
- Loose locking tabs
- Moisture intrusion
Poor PCM connections may reduce sensor signal voltage.
Step 17 – Verify PCM Software
Verify the PCM is running the latest available software calibration.
Manufacturers occasionally release updates correcting:
- False P0187 detection
- Fuel temperature calculations
- Sensor calibration logic
- Diagnostic sensitivity
Always update PCM software before considering module replacement.
Step 18 – Perform a Wiggle Test
While monitoring live scan-tool data:
Move:
- Wiring harness
- Sensor connector
- Fuel Composition Sensor
- PCM harness
If voltage suddenly changes, inspect for:
- Broken wiring
- Loose connectors
- Internal conductor damage
Step 19 – Perform a Road Test
After repairs:
Monitor:
- Fuel Temperature Sensor “B”
- Fuel trims
- Battery voltage
- Pending DTCs
Complete a normal drive cycle while observing live scan-tool data.
Step 20 – Confirm the Diagnosis
Before replacing major components, verify:
- Sensor resistance
- Sensor voltage
- Wiring continuity
- Connector condition
- Reference voltage
- Ground integrity
- Short-to-ground testing
- PCM software
Completing these diagnostic procedures prevents unnecessary parts replacement while accurately identifying the root cause of P0187.
Step 21 – Replace Fuel Temperature Sensor “B”
If testing confirms Fuel Temperature Sensor “B” is producing a consistently low voltage signal or resistance values outside manufacturer specifications, replacement is the proper repair.
General replacement procedure:
- Relieve fuel system pressure according to the manufacturer’s service procedures.
- Disconnect the negative battery cable.
- Disconnect the Fuel Temperature Sensor “B” electrical connector.
- Remove the sensor or Fuel Composition Sensor assembly if the sensor is integrated.
- Install an OEM-quality replacement component.
- Reconnect all electrical connectors and fuel system components.
- Clear all diagnostic trouble codes.
- Verify proper Fuel Temperature Sensor “B” operation using a professional scan tool.
Many manufacturers integrate Fuel Temperature Sensor “B” into the Fuel Composition Sensor or fuel pump module, requiring replacement of the complete assembly.
Step 22 – Repair Wiring Problems
P0187 is frequently caused by damaged wiring that reduces sensor voltage.
Inspect and repair:
- Short-to-ground faults
- Broken wiring
- Chafed insulation
- Melted wiring
- Pinched harnesses
- Rodent damage
Whenever possible:
- Solder wire repairs
- Protect repairs with adhesive-lined heat-shrink tubing
- Follow OEM wiring repair procedures
Improper wiring repairs often result in recurring low-voltage faults.
Step 23 – Repair Electrical Connectors
Inspect every connector between Fuel Temperature Sensor “B” and the PCM.
Repair:
- Corroded terminals
- Bent connector pins
- Loose locking tabs
- Weak terminal tension
- Moisture intrusion
- Fuel contamination
- Damaged connector housings
Poor connector contact commonly lowers circuit voltage enough to trigger P0187.
Step 24 – Restore Proper Power and Ground
Using manufacturer wiring diagrams:
Verify:
- Reference voltage
- Ignition voltage (if applicable)
- Ground integrity
Repair:
- Corroded ground points
- Loose grounds
- Damaged wiring
- Low reference voltage circuits
Stable voltage and a solid ground are essential for accurate Fuel Temperature Sensor “B” operation.
Step 25 – Repair Short-to-Ground Faults
One of the most common causes of P0187 is a short-to-ground.
Inspect and repair:
- Signal wire contacting chassis ground
- Damaged insulation
- Pinched harnesses
- Harnesses rubbing against engine or frame components
- Crushed wiring
After repairs, verify there is no continuity between the signal wire and ground unless specified by the manufacturer.
Step 26 – Verify Sensor Voltage
After repairs:
Monitor live scan-tool data while measuring sensor voltage.
Verify:
- Stable voltage
- Proper response to changing fuel temperature
- Smooth signal changes
- No low-voltage conditions
Fuel Temperature Sensor “B” should remain within manufacturer specifications throughout engine operation.
Step 27 – Compare Sensor “A” and Sensor “B”
If the vehicle uses multiple Fuel Temperature Sensors:
Compare:
- Fuel Temperature Sensor “A”
- Fuel Temperature Sensor “B”
Both sensors should display logical values based on their locations within the fuel system.
Large unexplained differences may indicate:
- Incorrect replacement sensor
- Wiring resistance
- Fuel Composition Sensor issues
- Calibration problems
Step 28 – Update PCM Software
Before replacing expensive components:
Review manufacturer Technical Service Bulletins (TSBs).
Manufacturers occasionally release PCM updates correcting:
- False P0187 detection
- Fuel temperature calculation errors
- Sensor calibration logic
- Diagnostic sensitivity
Always verify the PCM has the latest available software calibration.
Step 29 – Verify Proper System Operation
After repairs:
Monitor:
- Fuel Temperature Sensor “B”
- Battery voltage
- Fuel trims
- Pending DTCs
Complete a full OBD-II drive cycle while monitoring live scan-tool data.
No diagnostic trouble codes should return.
Step 30 – Consider PCM Failure
PCM failure is extremely uncommon.
Only suspect the PCM after confirming:
- Proper Fuel Temperature Sensor “B” operation
- Correct sensor resistance
- Stable sensor voltage
- Wiring continuity
- Connector integrity
- Proper reference voltage
- Good ground
- Updated PCM software
PCM replacement should always be the final diagnostic step.
How to Fix P0187
The proper repair depends entirely on the diagnostic results.
Common repairs include:
- Replacing Fuel Temperature Sensor “B”
- Replacing the Fuel Composition Sensor assembly (if integrated)
- Repairing damaged wiring
- Repairing short-to-ground faults
- Repairing low reference voltage circuits
- Cleaning or replacing corroded connectors
- Restoring proper power and ground
- Updating PCM software
- Replacing the PCM (rare)
Verifying the Repair
After completing repairs:
- Clear all diagnostic trouble codes.
- Start the engine.
- Allow the engine to reach operating temperature.
- Monitor Fuel Temperature Sensor “B” live data.
- Compare Sensor “A” and Sensor “B” readings when applicable.
- Perform a complete road test.
- Complete an OBD-II drive cycle.
- Verify no pending or permanent DTCs return.
- Perform a final scan confirming normal Fuel Temperature Sensor “B” operation.
A successful repair restores accurate fuel temperature monitoring, proper fuel calculations, improved drivability, fuel economy, and emissions compliance.
Typical Repair Costs
| Repair | Typical Cost |
|---|---|
| Professional diagnosis | $100–250 |
| Fuel Temperature Sensor “B” replacement | $150–450 |
| Fuel Composition Sensor replacement | $250–700 |
| Wiring repair | $100–500 |
| Connector replacement | $75–250 |
| Fuel pump module replacement (if integrated) | $500–1,400 |
| PCM software update | $100–250 |
| PCM replacement | $800–2,000+ |
Repair costs vary depending on vehicle design, labor rates, and whether Fuel Temperature Sensor “B” is serviced separately or integrated into another component.
Common Diagnostic Mistakes
Avoid these common mistakes:
- Replacing Fuel Temperature Sensor “B” before testing the circuit
- Ignoring short-to-ground faults
- Overlooking corroded connectors
- Skipping reference voltage testing
- Clearing codes before recording freeze-frame data
- Ignoring Technical Service Bulletins
- Replacing the PCM before completing electrical testing
Many P0187 repairs involve correcting wiring or grounding problems rather than replacing the sensor.
Manufacturer-Specific Notes
General Motors (Chevrolet, GMC, Cadillac, Buick)
Inspect:
- Fuel Composition Sensor assembly
- Fuel Temperature Sensor “B” wiring
- Frame-mounted harnesses
- PCM software
Many GM flex-fuel vehicles integrate Fuel Temperature Sensor “B” into the Fuel Composition Sensor.
Ford/Lincoln
Verify:
- Sensor voltage
- Harness integrity
- Connector condition
- PCM calibration
Ford trucks commonly develop wiring damage near frame-mounted harnesses.
Chrysler, Dodge, Jeep, Ram
Inspect:
- Harness routing
- Connector corrosion
- Fuel pump module wiring
- PCM software updates
Heat damage near exhaust components frequently contributes to low-voltage faults.
Toyota/Lexus
Fuel Temperature Sensor “B” failures are relatively uncommon. Thoroughly inspect wiring, connectors, and reference voltage before replacing components.
Nissan/Infiniti
Verify:
- Sensor resistance
- Harness continuity
- Connector condition
- PCM software
Some Nissan models integrate Fuel Temperature Sensor “B” into the fuel pump module.
Hyundai/Kia
Inspect:
- Wiring harness
- Connector terminals
- Ground circuits
- Fuel pump module wiring
Electrical faults remain significantly more common than PCM failures.
Frequently Asked Questions
What usually fixes P0187?
The most common repairs include replacing Fuel Temperature Sensor “B,” repairing short-to-ground faults, repairing damaged wiring, restoring proper reference voltage, cleaning or replacing corroded connectors, updating PCM software, or replacing the Fuel Composition Sensor assembly if the sensor is integrated.
Can I drive with P0187?
Usually, yes. Most vehicles remain drivable using backup fuel calculations, but fuel economy, emissions, and drivability may suffer until repairs are completed.
Does P0187 always mean Fuel Temperature Sensor “B” is bad?
No. Short-to-ground faults, damaged wiring, low reference voltage, connector corrosion, poor ground connections, and PCM software issues frequently trigger P0187 without complete sensor failure.
Can bad wiring trigger P0187?
Absolutely. Broken wiring, damaged insulation, short-to-ground faults, loose connectors, and excessive voltage drop are among the most common causes of P0187.
Is P0187 a serious code?
P0187 is generally considered a moderate severity diagnostic trouble code. If ignored, it can reduce fuel economy, increase emissions, affect engine performance, and prevent the PCM from accurately calculating fuel temperature.
Final Thoughts
The P0187 Fuel Temperature Sensor “B” Circuit Low Input code indicates the PCM has detected a voltage signal below the expected operating range from Fuel Temperature Sensor “B”. In most cases, the root cause is a failing sensor, short-to-ground, damaged wiring, low reference voltage, connector corrosion, or poor electrical connections, rather than PCM failure.
A complete diagnosis should always verify:
- Fuel Temperature Sensor “B” resistance
- Sensor voltage
- Wiring continuity
- Connector condition
- Reference voltage
- Ground integrity
- Short-to-ground testing
- PCM software level
Following a systematic diagnostic process prevents unnecessary parts replacement while restoring accurate fuel temperature monitoring, proper engine calibration, improved fuel economy, and long-term reliability.
Continue Your Pro Street Fuel System Series
Related guides include:
- P0185 – Fuel Temperature Sensor “B” Circuit Malfunction
- P0186 – Fuel Temperature Sensor “B” Circuit Range/Performance
- P0188 – Fuel Temperature Sensor “B” Circuit High Input
- P0189 – Fuel Temperature Sensor “B” Circuit Intermittent
- P0182 – Fuel Temperature Sensor “A” Circuit Low Input
- P0183 – Fuel Temperature Sensor “A” Circuit High Input
