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P0185 Code Explained: Fuel Temperature Sensor “B” Circuit Malfunction Causes, Symptoms & Fixes

P0185 code illustration showing Fuel Temperature Sensor "B", damaged wiring, electrical circuit warning, Check Engine Light, Pro Street TV logo, and www.ProStreetOnline.com.

If your OBD-II scanner displays P0185, your vehicle’s Engine Control Module (ECM) or Powertrain Control Module (PCM) has detected an electrical malfunction in the Fuel Temperature Sensor “B” circuit.

The generic OBD-II definition for P0185 is:

Fuel Temperature Sensor “B” Circuit Malfunction

Unlike P0180, which applies to Fuel Temperature Sensor “A”, P0185 refers specifically to Fuel Temperature Sensor “B” on vehicles equipped with multiple fuel temperature sensors. The PCM has detected an electrical problem within the Sensor “B” circuit that prevents it from accurately monitoring fuel temperature.

Many modern gasoline, diesel, and flex-fuel vehicles use multiple fuel temperature sensors to improve:

Common causes include:

Without accurate fuel temperature information from Sensor “B,” the PCM may use backup fuel calculations that reduce fuel economy and overall engine efficiency.

What Does the P0185 Code Mean?

The PCM continuously monitors Fuel Temperature Sensor “B” to determine the temperature of fuel within a specific section of the fuel system.

Fuel temperature affects:

If the PCM detects an electrical fault that prevents proper communication with Fuel Temperature Sensor “B,” it stores P0185.

Unlike a performance code, P0185 indicates the circuit itself has developed an electrical problem, not necessarily that the temperature reading is inaccurate.

What Is Fuel Temperature Sensor “B”?

Fuel Temperature Sensor “B” is an electronic thermistor that changes electrical resistance as fuel temperature changes.

Depending on the manufacturer, it may be located:

Vehicles equipped with multiple fuel temperature sensors use Sensor “B” to monitor temperature in a different section of the fuel system than Sensor “A.”

The PCM uses information from both sensors to improve:

Why Fuel Temperature Matters

Fuel changes density as temperature changes.

Cold fuel:

Hot fuel:

Accurate temperature information allows the PCM to optimize fuel delivery under changing operating conditions.

How the PCM Detects P0185

The PCM continuously monitors:

If the electrical circuit for Fuel Temperature Sensor “B” becomes:

the PCM stores P0185.

Most manufacturers require multiple failed monitoring events before illuminating the Check Engine Light.

What Does “Circuit Malfunction” Mean?

A Circuit Malfunction code indicates the PCM has detected an electrical fault somewhere within the sensor circuit.

Possible causes include:

Unlike performance-related codes, the PCM is identifying an electrical problem rather than inaccurate temperature readings.

Can Wiring Problems Cause P0185?

Absolutely.

Electrical wiring faults are one of the most common causes of P0185.

Inspect for:

Even minor wiring damage can interrupt communication between the sensor and PCM.

Can Fuel Temperature Sensor “B” Fail?

Yes.

Fuel Temperature Sensors gradually wear over time.

Common causes include:

Many sensors begin producing unstable electrical signals before failing completely.

Can Connector Corrosion Trigger P0185?

Yes.

Corroded electrical connectors frequently interrupt sensor communication.

Corrosion can cause:

Connector inspection should always be part of the diagnostic process.

P0185 Quick Facts

ItemInformation
DTCP0185
Generic DefinitionFuel Temperature Sensor “B” Circuit Malfunction
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, damaged wiring, connector corrosion, open or shorted circuits
Typical Repair Cost$100–900+
Related CodesP0186, P0187, P0188, P0189

Common Vehicles That Experience P0185

P0185 commonly appears on:

The code is primarily found on vehicles equipped with multiple Fuel Temperature Sensors or advanced flex-fuel management systems.

What Does P0185 Really Mean?

The wording of P0185 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 an electrical malfunction somewhere within the Fuel Temperature Sensor “B” circuit.

The underlying problem may involve:

Think of P0185 as the PCM saying:

“I’m unable to properly communicate with Fuel Temperature Sensor ‘B’ because there’s an electrical problem in its circuit.”

Common P0185 Scan Tool Patterns

Using a professional scan tool is one of the quickest ways to diagnose P0185.

Unlike P0186, which indicates a performance problem, P0187, which indicates a low-input condition, P0188, which indicates a high-input condition, or P0189, which indicates intermittent communication, P0185 means the PCM has detected a general electrical malfunction within the Fuel Temperature Sensor “B” circuit.

Modern scan tools may display:

Comparing these values helps determine whether the fault lies in the sensor, wiring, connectors, or the PCM.

Pattern 1: No Fuel Temperature Sensor “B” Data

One of the most common scan-tool patterns is:

Possible causes include:

The PCM cannot calculate fuel temperature when communication is lost.

Pattern 2: Frozen Fuel Temperature Reading

The scan tool may display:

Possible causes include:

A frozen reading usually indicates an electrical fault rather than actual fuel temperature.

Pattern 3: Fuel Temperature Sensor “B” Differs Greatly from Sensor “A”

On vehicles equipped with multiple sensors:

Possible causes include:

Comparing both sensors often speeds diagnosis.

Pattern 4: Sensor Communication Appears and Disappears

Some vehicles show:

Possible causes include:

This behavior may eventually develop into P0189 (Circuit Intermittent) if the condition worsens.

Pattern 5: Multiple Fuel Temperature Codes

P0185 commonly appears together with:

Multiple Fuel Temperature Sensor “B” codes usually indicate:

Pattern 6: Fuel Trim Changes

Although P0185 is not a fuel trim code, incorrect or missing fuel temperature information may affect:

Fuel trims may fluctuate as the PCM switches to default fuel calculations.

Pattern 7: Voltage Supply Problems

Monitor battery voltage with the scan tool.

Possible observations include:

Electrical supply problems may interfere with Fuel Temperature Sensor “B” operation.

Common Symptoms of P0185

Symptoms vary depending on how severe the circuit malfunction becomes.

Common symptoms include:

Some vehicles initially display only the Check Engine Light.

Check Engine Light

The Check Engine Light is usually the first symptom.

Most manufacturers require:

before storing P0185.

Hard Starting

Improper fuel temperature information may result in:

Cold weather often makes these symptoms more noticeable.

Reduced Fuel Economy

Without accurate Fuel Temperature Sensor “B” information, the PCM may use backup fuel calculations.

Drivers may notice:

Fuel economy often declines gradually.

Hesitation During Acceleration

Improper fuel calculations may produce:

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

Rough Idle

Incorrect fuel temperature information may result in:

Idle quality usually improves after restoring proper sensor communication.

Is P0185 Serious?

P0185 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 postponed.

Can You Drive With P0185?

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 strategies until repairs are completed.

P0185 vs Related Trouble Codes

Understanding related Fuel Temperature Sensor “B” codes simplifies diagnosis.

P0185

Fuel Temperature Sensor “B” Circuit Malfunction

The PCM detects a general electrical fault within the circuit.

P0186

Fuel Temperature Sensor “B” Circuit Range/Performance

The sensor communicates, but its readings fall outside expected operating limits.

P0187

Fuel Temperature Sensor “B” Circuit Low Input

The PCM detects sensor voltage below specification.

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 from the sensor.

30 Common Causes of P0185

The most common causes include:

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

Final Thoughts

The P0185 Fuel Temperature Sensor “B” Circuit Malfunction code indicates the PCM has detected an electrical fault affecting communication with Fuel Temperature Sensor “B”. In most cases, the root cause is a failed sensor, damaged wiring, connector corrosion, poor electrical connections, or an open or shorted circuit, rather than PCM failure.

Proper diagnosis should determine whether the fault originates in:

The next section of this guide covers:

Following a structured diagnostic process prevents unnecessary parts replacement while restoring accurate fuel temperature monitoring, proper fuel calculations, improved fuel economy, and emissions compliance.

Related Pro Street Diagnostic Guides

How to Diagnose the P0185 Code

Diagnosing P0185 requires determining why the PCM has detected an electrical malfunction in the Fuel Temperature Sensor “B” circuit.

Unlike P0186, which indicates inaccurate sensor performance, P0187, which indicates a low-voltage condition, P0188, which indicates a high-voltage condition, or P0189, which indicates intermittent communication, P0185 specifically means there is a continuous electrical fault affecting 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 measuring sensor voltage, resistance, and circuit continuity.

Step 1 – Verify the Code

Connect a professional scan tool.

Record:

Monitor:

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

Step 2 – Check for Related Trouble Codes

P0185 commonly appears with:

Related codes often narrow the diagnosis.

Code CombinationLikely Diagnosis
P0185 onlyGeneral circuit malfunction
P0185 + P0186Sensor performance issue
P0185 + P0187Low input fault
P0185 + P0188High input fault
P0185 + P0189Intermittent circuit fault

Repair related electrical faults before replacing additional components.

Step 3 – Review Freeze-Frame Data

Review:

Freeze-frame data often reveals the operating conditions that triggered the fault.

Step 4 – Locate Fuel Temperature Sensor “B”

Depending on vehicle design, Sensor “B” may be located:

Consult the factory service manual before removing components.

Step 5 – Inspect Fuel Temperature Sensor “B”

Inspect the sensor for:

Visible damage may justify replacement after electrical testing.

Step 6 – Inspect the Wiring Harness

Inspect the wiring between Fuel Temperature Sensor “B” and the PCM.

Look for:

Open circuits and damaged wiring are among the most common causes of P0185.

Step 7 – Inspect the Electrical Connector

Disconnect the sensor connector.

Inspect for:

Poor electrical connections frequently trigger P0185.

Step 8 – Verify Reference Voltage

Using a digital multimeter:

Measure:

Compare readings with manufacturer specifications.

Incorrect reference voltage may indicate wiring or PCM issues.

Step 9 – Verify Ground Integrity

Measure voltage drop across the sensor ground.

Inspect for:

A poor ground can interrupt Fuel Temperature Sensor “B” communication.

Step 10 – Measure Sensor Resistance

Most Fuel Temperature Sensors are thermistors.

Disconnect the sensor.

Measure resistance using a digital multimeter.

Compare readings with manufacturer specifications for the current fuel temperature.

Readings outside specification usually indicate sensor failure.

Step 11 – Measure Sensor Voltage

Reconnect the sensor.

Back-probe the signal wire.

Monitor voltage while the engine warms up.

Verify:

Abnormal voltage indicates additional circuit diagnosis is required.

Step 12 – Compare Actual Fuel Temperature

Use an infrared thermometer to measure:

Compare actual temperatures with scan-tool readings.

Large differences suggest:

Step 13 – Review Technical Service Bulletins

Before replacing expensive components:

Review manufacturer Technical Service Bulletins (TSBs).

Look for:

Some manufacturers have released updates correcting false P0185 detection.

Step 14 – Inspect Previous Repairs

Inspect for:

Many circuit malfunctions begin after unrelated repairs.

Step 15 – Verify Charging System Voltage

Measure charging voltage.

Normal charging voltage:

13.5–14.8 volts

Electrical system problems can interfere with sensor operation.

Step 16 – Perform a Wiggle Test

While monitoring live scan-tool data:

Move:

If communication changes:

Suspect:

Even continuous circuit faults can worsen when wiring is moved.

Step 17 – Inspect PCM Connector Pins

Inspect PCM connectors for:

Poor PCM connections may interrupt communication with Fuel Temperature Sensor “B”.

Step 18 – Verify PCM Software

Verify the PCM is running the latest available software calibration.

Manufacturers occasionally release updates correcting:

Always install available software updates before replacing the PCM.

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 P0185.

Step 21 – Replace Fuel Temperature Sensor “B”

If testing confirms Fuel Temperature Sensor “B” has failed electrically or is operating outside manufacturer specifications, replacement is the proper repair.

General replacement procedure:

  1. Relieve fuel system pressure following the manufacturer’s 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 with 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

P0185 is frequently caused by damaged wiring between Fuel Temperature Sensor “B” and the PCM.

Inspect and repair:

Whenever possible:

Improper wiring repairs often result in recurring electrical faults.

Step 23 – Repair Electrical Connectors

Inspect every connector between Fuel Temperature Sensor “B” and the PCM.

Repair:

Poor connector contact is one of the leading causes of P0185.

Step 24 – Restore Proper Power and Ground

Using manufacturer wiring diagrams:

Verify:

Repair:

Stable voltage and ground are essential for accurate Fuel Temperature Sensor “B” operation.

Step 25 – Repair Circuit Faults

If electrical testing identifies a circuit problem:

Repair:

After repairs, verify circuit continuity before reconnecting the PCM and sensor.

Step 26 – Verify Sensor Operation

After repairs:

Monitor live scan-tool data.

Verify:

Fuel Temperature Sensor “B” should operate normally throughout the drive cycle.

Step 27 – Compare Sensor “A” and Sensor “B” Data

On vehicles equipped with multiple Fuel Temperature Sensors:

Compare:

Both sensors should display logical temperature values based on operating conditions.

Large 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 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 P0185

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. Perform a complete road test.
  6. Complete an OBD-II drive cycle.
  7. Verify no pending or permanent DTCs return.
  8. 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 P0185 repairs involve repairing wiring or connector 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 can affect sensor wiring.

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 are significantly more common than PCM failures.

Frequently Asked Questions

What usually fixes P0185?

The most common repairs include replacing Fuel Temperature Sensor “B,” repairing damaged wiring, correcting open or short circuits, cleaning or replacing corroded connectors, restoring proper power and ground, updating PCM software, or replacing the Fuel Composition Sensor assembly if the sensor is integrated.

Can I drive with P0185?

Usually, yes. Most vehicles remain drivable using backup fuel calculations, but fuel economy, emissions, and drivability may suffer until repairs are completed.

Does P0185 always mean Fuel Temperature Sensor “B” is bad?

No. Damaged wiring, connector corrosion, open circuits, short circuits, poor grounds, and PCM software issues frequently trigger P0185 without complete sensor failure.

Can bad wiring trigger P0185?

Absolutely. Broken wiring, high-resistance circuits, loose connectors, open circuits, and short circuits are among the most common causes of P0185.

Is P0185 a serious code?

P0185 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 P0185 Fuel Temperature Sensor “B” Circuit Malfunction code indicates the PCM has detected an electrical fault affecting communication with Fuel Temperature Sensor “B”. In most cases, the root cause is a failing sensor, damaged wiring, open or shorted circuits, 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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