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P0187 Code Explained: Fuel Temperature Sensor “B” Circuit Low Input Causes, Symptoms & Fixes

P0187 code illustration showing Fuel Temperature Sensor "B", low voltage warning, damaged wiring, Check Engine Light, Pro Street TV logo, and www.ProStreetOnline.com.

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:

Common causes include:

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:

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:

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:

Why Fuel Temperature Matters

Fuel density changes as temperature changes.

Cold fuel:

Hot fuel:

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:

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:

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:

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:

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:

Always verify reference voltage before replacing the sensor.

P0187 Quick Facts

ItemInformation
DTCP0187
Generic DefinitionFuel Temperature Sensor “B” Circuit Low Input
SystemFuel & Air Management
SeverityModerate
Safe to Drive?Usually, but repairs should not be delayed
Common SymptomsCheck Engine Light, poor fuel economy, hesitation, hard starting
Common CausesFailed sensor, short-to-ground, damaged wiring, low reference voltage
Typical Repair Cost$100–900+
Related CodesP0185, P0186, P0188, P0189

Common Vehicles That Experience P0187

P0187 commonly appears on:

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:

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:

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:

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:

Possible causes include:

The PCM interprets the low voltage as an abnormally low fuel temperature.

Pattern 2: Fuel Temperature Never Changes

The scan tool may display:

Possible causes include:

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:

Possible causes include:

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:

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:

Multiple Fuel Temperature Sensor “B” codes often indicate:

Pattern 6: Fuel Trim Changes

Although P0187 is not a fuel trim code, incorrect fuel temperature calculations may affect:

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:

These conditions commonly trigger P0187.

Common Symptoms of P0187

Symptoms vary depending on how low the sensor voltage becomes.

Common symptoms include:

Some vehicles initially exhibit only the Check Engine Light.

Check Engine Light

The Check Engine Light is usually the first symptom.

Most manufacturers require:

before storing P0187.

Hard Starting

Incorrect fuel temperature information may result in:

Cold-weather operation may make these symptoms more noticeable.

Reduced Fuel Economy

Incorrect fuel density calculations may cause:

Fuel economy often declines gradually.

Hesitation During Acceleration

Improper fuel calculations may produce:

Performance issues are generally mild unless additional fuel system faults are present.

Rough Idle

Incorrect Fuel Temperature Sensor “B” readings may result in:

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:

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:

Stop driving immediately if:

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:

  1. Failed Fuel Temperature Sensor “B”
  2. Short-to-ground
  3. Low reference voltage
  4. Damaged wiring
  5. Broken wiring harness
  6. High circuit resistance
  7. Connector corrosion
  8. Loose electrical connectors
  9. Poor ground connection
  10. Moisture intrusion
  11. Heat-damaged wiring
  12. Rodent damage
  13. Fuel Composition Sensor failure
  14. Internal thermistor failure
  15. Fuel contamination
  16. Weak battery
  17. Charging system faults
  18. Connector pin damage
  19. Corroded ground point
  20. Improper aftermarket wiring repairs
  21. Harness routing problems
  22. Electrical interference
  23. Manufacturing defect
  24. PCM software issue
  25. Failed PCM (rare)
  26. Fuel pump module wiring damage
  27. Low system voltage
  28. Water intrusion into connectors
  29. Incorrect replacement sensor
  30. 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:

The next section of this guide covers:

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

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:

Proper diagnosis requires testing the entire Fuel Temperature Sensor “B” circuit, not simply replacing the sensor.

Safety Precautions

Before beginning diagnosis:

Always follow the manufacturer’s service procedures before disconnecting fuel system components.

Tools Required

Professional diagnosis may require:

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:

Monitor:

Always save freeze-frame information before clearing any diagnostic trouble codes.

Step 2 – Check for Related Trouble Codes

P0187 commonly appears with:

Related codes often simplify diagnosis.

Code CombinationLikely Diagnosis
P0187 onlyLow input fault
P0187 + P0185General circuit malfunction
P0187 + P0186Sensor performance issue
P0187 + P0188Voltage instability
P0187 + P0189Intermittent wiring fault

Repair any additional electrical faults before replacing components.

Step 3 – Review Freeze-Frame Data

Review:

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:

Consult the factory service manual before removing any components.

Step 5 – Inspect Fuel Temperature Sensor “B”

Inspect the sensor for:

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:

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:

Poor terminal contact often lowers sensor voltage.

Step 8 – Verify Reference Voltage

Using a digital multimeter:

Measure:

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:

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:

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:

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:

Compare actual temperatures with scan-tool readings.

Large differences suggest:

Step 14 – Review Technical Service Bulletins

Before replacing expensive components:

Review manufacturer Technical Service Bulletins (TSBs).

Look for:

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:

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:

Always update PCM software before considering module replacement.

Step 18 – Perform a Wiggle Test

While monitoring live scan-tool data:

Move:

If voltage suddenly changes, inspect for:

Step 19 – Perform a Road Test

After repairs:

Monitor:

Complete a normal drive cycle while observing live scan-tool data.

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 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:

  1. Relieve fuel system pressure according to the manufacturer’s service procedures.
  2. Disconnect the negative battery cable.
  3. Disconnect the Fuel Temperature Sensor “B” electrical connector.
  4. Remove the sensor or Fuel Composition Sensor assembly if the sensor is integrated.
  5. Install an OEM-quality replacement component.
  6. Reconnect all electrical connectors and fuel system components.
  7. Clear all diagnostic trouble codes.
  8. 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:

Whenever possible:

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:

Poor connector contact commonly lowers circuit voltage enough to trigger P0187.

Step 24 – Restore Proper Power and Ground

Using manufacturer wiring diagrams:

Verify:

Repair:

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:

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:

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:

Both sensors should display logical values based on their locations within the fuel system.

Large unexplained differences may indicate:

Step 28 – Update PCM Software

Before replacing expensive components:

Review manufacturer Technical Service Bulletins (TSBs).

Manufacturers occasionally release PCM updates correcting:

Always verify the PCM has the latest available software calibration.

Step 29 – Verify Proper System Operation

After repairs:

Monitor:

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:

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:

Verifying the Repair

After completing repairs:

  1. Clear all diagnostic trouble codes.
  2. Start the engine.
  3. Allow the engine to reach operating temperature.
  4. Monitor Fuel Temperature Sensor “B” live data.
  5. Compare Sensor “A” and Sensor “B” readings when applicable.
  6. Perform a complete road test.
  7. Complete an OBD-II drive cycle.
  8. Verify no pending or permanent DTCs return.
  9. 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

RepairTypical 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:

Many P0187 repairs involve correcting wiring or grounding problems rather than replacing the sensor.

Manufacturer-Specific Notes

General Motors (Chevrolet, GMC, Cadillac, Buick)

Inspect:

Many GM flex-fuel vehicles integrate Fuel Temperature Sensor “B” into the Fuel Composition Sensor.

Ford/Lincoln

Verify:

Ford trucks commonly develop wiring damage near frame-mounted harnesses.

Chrysler, Dodge, Jeep, Ram

Inspect:

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:

Some Nissan models integrate Fuel Temperature Sensor “B” into the fuel pump module.

Hyundai/Kia

Inspect:

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:

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:

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