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P0189 Code Explained: Fuel Temperature Sensor “B” Circuit Intermittent Causes, Symptoms & Fixes

P0189 code illustration showing Fuel Temperature Sensor "B", intermittent wiring fault, unstable signal, Check Engine Light, Pro Street TV logo, and www.ProStreetOnline.com.

If your OBD-II scanner displays P0189, your vehicle’s Engine Control Module (ECM) or Powertrain Control Module (PCM) has detected an intermittent electrical problem in the Fuel Temperature Sensor “B” circuit.

The generic OBD-II definition for P0189 is:

Fuel Temperature Sensor “B” Circuit Intermittent

Unlike P0185, which indicates a general circuit malfunction, P0186, which indicates a sensor performance problem, P0187, which indicates a low-input condition, or P0188, which indicates a high-input condition, P0189 means the Fuel Temperature Sensor “B” signal is unstable, dropping out, or changing unexpectedly.

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

Common causes include:

Because the signal is unreliable, the PCM may switch between normal and backup fuel calculations, causing symptoms that appear and disappear like an electrical ghost with commitment issues.

What Does the P0189 Code Mean?

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

Fuel temperature affects:

If the PCM detects that the sensor signal repeatedly:

it stores P0189.

Unlike a continuous circuit fault, P0189 indicates the circuit works sometimes and fails at others.

What Is Fuel Temperature Sensor “B”?

Fuel Temperature Sensor “B” is an electronic thermistor that changes resistance 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 different part of the fuel system than Sensor “A.”

The PCM uses Sensor “B” data to optimize:

Why Fuel Temperature Matters

Fuel density changes as temperature changes.

Cold fuel:

Hot fuel:

When the signal becomes intermittent, the PCM cannot consistently calculate fuel density and may rely on backup values.

How the PCM Detects P0189

The PCM continuously monitors:

If Fuel Temperature Sensor “B” communication repeatedly disappears or becomes erratic, the PCM stores P0189.

Most manufacturers require several intermittent failures before illuminating the Check Engine Light.

What Does “Circuit Intermittent” Mean?

A Circuit Intermittent code means the electrical fault is not present all the time.

The circuit may:

These faults are often harder to diagnose because the vehicle may behave normally in the repair bay.

Can Wiring Problems Cause P0189?

Absolutely.

Wiring and connector faults are among the most common causes of P0189.

Inspect for:

A wire can look perfect on the outside while being broken internally. Automotive wiring occasionally enjoys lying to your face.

Can Fuel Temperature Sensor “B” Fail Intermittently?

Yes.

Sensors often fail intermittently before failing completely.

Common causes include:

Symptoms may become more frequent as the sensor deteriorates.

Can Moisture Cause P0189?

Yes.

Moisture entering the connector may cause:

P0189 may appear only during rain, high humidity, or after washing the engine bay.

Can Vibration Trigger P0189?

Yes.

Vehicle vibration may temporarily interrupt a weak connection.

Common problem areas include:

If the code appears after driving over rough roads, wiring movement should be strongly suspected.

P0189 Quick Facts

ItemInformation
DTCP0189
Generic DefinitionFuel Temperature Sensor “B” Circuit Intermittent
SystemFuel & Air Management
SeverityModerate
Safe to Drive?Usually, but repairs should not be delayed
Common SymptomsCheck Engine Light, intermittent hesitation, rough idle, hard starting
Common CausesLoose connectors, broken wiring, sensor failure, moisture intrusion
Typical Repair Cost$100–900+
Related CodesP0185, P0186, P0187, P0188

Common Vehicles That Experience P0189

P0189 may appear on:

The code is most common on vehicles equipped with multiple fuel temperature sensors, flex-fuel systems, or advanced fuel management systems.

What Does P0189 Really Mean?

The wording of P0189 often causes drivers to assume Fuel Temperature Sensor “B” has failed completely.

The code does not automatically mean:

Instead, it means the PCM has detected an unstable or interrupted signal from Fuel Temperature Sensor “B”.

The underlying problem may involve:

Think of P0189 as the PCM saying:

“Fuel Temperature Sensor ‘B’ works sometimes, disappears at others, and generally behaves like it has somewhere better to be.”

Common P0189 Scan Tool Patterns

Using a professional scan tool is one of the best ways to diagnose P0189.

Unlike P0185, which indicates a general circuit malfunction, P0186, which indicates a performance problem, P0187, which indicates a low-voltage condition, or P0188, which indicates a high-voltage condition, P0189 means the Fuel Temperature Sensor “B” signal repeatedly becomes unstable, disappears, or returns unexpectedly.

Modern scan tools may display:

Watching live data over time is often the fastest way to identify an intermittent fault.

Pattern 1: Fuel Temperature Signal Drops Out

One of the most common scan-tool patterns is:

Possible causes include:

These intermittent dropouts are the hallmark of P0189.

Pattern 2: Fuel Temperature Suddenly Jumps

The scan tool may display:

Possible causes include:

Abrupt changes without actual fuel temperature changes usually indicate an electrical fault.

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

On vehicles equipped with multiple sensors:

Possible causes include:

Comparing both sensors during a road test often exposes the problem.

Pattern 4: Signal Changes When the Harness Is Moved

While observing live scan-tool data:

Possible causes include:

This is one of the strongest indicators of an intermittent wiring fault.

Pattern 5: Multiple Fuel Temperature Codes

P0189 commonly appears together with:

Multiple Fuel Temperature Sensor “B” codes usually indicate:

Pattern 6: Fuel Trim Fluctuations

Although P0189 is not a fuel trim code, intermittent fuel temperature data may cause:

The PCM continually switches between live sensor input and backup calculations.

Pattern 7: Problem Appears Only Under Certain Conditions

P0189 often occurs only when:

If the fault cannot be duplicated in the shop, a road test may be required.

Common Symptoms of P0189

Symptoms often come and go because the electrical fault is intermittent.

Common symptoms include:

Some vehicles may operate normally for days before symptoms return.

Check Engine Light

The Check Engine Light is usually the first symptom.

Most manufacturers require:

before storing P0189.

Intermittent Hard Starting

Incorrect fuel temperature information may occasionally result in:

Because the problem is intermittent, starting performance may vary from day to day.

Intermittent Hesitation

Drivers may notice:

These symptoms often disappear as quickly as they appear.

Rough Idle

Intermittent sensor communication may result in:

Idle quality usually changes only while the sensor signal is unstable.

Reduced Fuel Economy

When the PCM repeatedly switches to backup fuel calculations, drivers may notice:

The reduction is usually gradual and inconsistent.

Is P0189 Serious?

P0189 is generally considered a moderate severity diagnostic trouble code.

Ignoring the problem may eventually result in:

Intermittent problems often become permanent over time.

Can You Drive With P0189?

Usually, yes—but repairs should be completed as soon as practical.

Driving is generally safe if:

Stop driving immediately if:

Because intermittent faults tend to worsen, repairs should not be delayed.

P0189 vs Related Trouble Codes

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

P0189

Fuel Temperature Sensor “B” Circuit Intermittent

The PCM detects an unstable or intermittent sensor signal.

P0185

Fuel Temperature Sensor “B” Circuit Malfunction

The PCM detects a continuous electrical circuit fault.

P0186

Fuel Temperature Sensor “B” Circuit Range/Performance

The sensor communicates but reports implausible temperature data.

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.

30 Common Causes of P0189

The most common causes include:

  1. Failing Fuel Temperature Sensor “B”
  2. Loose electrical connector
  3. Broken wiring inside insulation
  4. Connector corrosion
  5. Moisture intrusion
  6. Intermittent short-to-ground
  7. Intermittent short-to-voltage
  8. Poor ground connection
  9. High circuit resistance
  10. Weak terminal tension
  11. Damaged wiring harness
  12. Heat-damaged wiring
  13. Harness movement
  14. Engine vibration
  15. Rodent damage
  16. Fuel Composition Sensor failure
  17. Internal thermistor failure
  18. Fuel contamination
  19. Connector pin damage
  20. Corroded ground point
  21. Improper aftermarket wiring repairs
  22. Harness routing problems
  23. Electrical interference
  24. Charging system voltage fluctuations
  25. PCM software issue
  26. Failed PCM (rare)
  27. Water intrusion after washing the engine
  28. Loose PCM connector
  29. Manufacturing defect
  30. Aging electrical components

Final Thoughts

The P0189 Fuel Temperature Sensor “B” Circuit Intermittent code indicates the PCM has detected an unstable or interrupted signal from Fuel Temperature Sensor “B”. In most cases, the root cause is a failing sensor, loose connector, damaged wiring, connector corrosion, moisture intrusion, or an intermittent short, 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 reliable fuel temperature monitoring, proper fuel delivery, improved fuel economy, and long-term reliability.

Related Pro Street Diagnostic Guides

How to Diagnose the P0189 Code

Diagnosing P0189 requires determining why Fuel Temperature Sensor “B” is producing an intermittent or unstable electrical signal.

Unlike P0185, which indicates a continuous circuit malfunction, P0186, which indicates a performance problem, P0187, which indicates a low-voltage condition, or P0188, which indicates a high-voltage condition, P0189 specifically means the PCM is losing communication with Fuel Temperature Sensor “B” only occasionally.

The underlying problem may involve:

Because the fault is intermittent, diagnosis often requires patience and live-data monitoring while attempting to duplicate the problem.

Safety Precautions

Before beginning diagnosis:

Always follow manufacturer safety procedures before disconnecting fuel system components.

Tools Required

Professional diagnosis may require:

A scan tool capable of recording live data is extremely helpful because intermittent failures may only occur for a fraction of a second.

Step 1 – Verify the Code

Connect a professional scan tool.

Record:

Monitor:

Never clear diagnostic trouble codes until freeze-frame information has been saved.

Step 2 – Check for Related Trouble Codes

P0189 commonly appears with:

Related codes often narrow the diagnosis.

Code CombinationLikely Diagnosis
P0189 onlyIntermittent signal loss
P0189 + P0185Circuit malfunction
P0189 + P0186Sensor performance issue
P0189 + P0187Intermittent low voltage
P0189 + P0188Intermittent high voltage

Repair any obvious electrical faults before replacing components.

Step 3 – Review Freeze-Frame Data

Review:

Freeze-frame data often reveals when the intermittent 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 components.

Step 5 – Inspect Fuel Temperature Sensor “B”

Inspect the sensor for:

Many intermittent faults begin with damaged sensor housings or loose connectors.

Step 6 – Inspect the Wiring Harness

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

Look for:

Flex the harness while inspecting, as internal conductor breaks may not be visible.

Step 7 – Inspect the Electrical Connector

Disconnect the sensor connector.

Inspect for:

Even a slightly loose terminal can create an intermittent connection.

Step 8 – Verify Reference Voltage

Using a digital multimeter:

Measure:

Compare readings with manufacturer specifications.

Reference voltage should remain stable while gently moving the wiring harness.

Step 9 – Verify Ground Integrity

Measure voltage drop across the sensor ground.

Inspect for:

Intermittent grounds commonly trigger P0189.

Step 10 – Measure Sensor Resistance

Disconnect the sensor.

Measure resistance using a digital multimeter.

Compare readings with manufacturer specifications at the current fuel temperature.

Repeat the test while gently moving the sensor connector and harness.

Resistance that suddenly changes indicates an intermittent fault.

Step 11 – Monitor Live Sensor Voltage

Reconnect the sensor.

Back-probe the signal wire.

Monitor live voltage while:

Watch for:

Step 12 – Perform a Wiggle Test

With the scan tool displaying live Fuel Temperature Sensor “B” data:

Carefully move:

If the signal changes while components are moved:

Inspect for:

The wiggle test is one of the most effective methods for diagnosing P0189.

Step 13 – Compare Actual Fuel Temperature

Use an infrared thermometer to measure:

Compare actual temperatures with scan-tool readings.

Large differences that appear only occasionally strongly suggest an intermittent sensor or wiring fault.

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 intermittent Fuel Temperature Sensor faults.

Step 15 – Verify Charging System Voltage

Measure charging voltage.

Normal charging voltage:

13.5–14.8 volts

Large voltage fluctuations may contribute to intermittent sensor communication problems.

Step 16 – Inspect PCM Connector Pins

Inspect PCM connectors for:

Intermittent PCM connections can mimic sensor failures.

Step 17 – Verify PCM Software

Verify the PCM is running the latest available software calibration.

Manufacturers occasionally release updates correcting:

Always install software updates before considering PCM replacement.

Step 18 – Perform an Extended Road Test

Because intermittent faults often disappear in the repair bay:

Drive the vehicle under various conditions:

Monitor live Fuel Temperature Sensor “B” data throughout the drive.

Step 19 – Use Data Recording

If available, enable scan-tool recording.

Capture:

Recording allows intermittent failures to be reviewed after they occur.

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 P0189.

Step 21 – Replace Fuel Temperature Sensor “B”

If testing confirms Fuel Temperature Sensor “B” is intermittently failing, 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 Intermittent Wiring Problems

P0189 is most commonly caused by intermittent wiring faults.

Inspect and repair:

Whenever possible:

Intermittent wiring failures often disappear temporarily after moving the harness, making them easy to overlook.

Step 23 – Repair Electrical Connectors

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

Repair:

Even slight connector movement can interrupt sensor communication long enough to trigger P0189.

Step 24 – Restore Proper Power and Ground

Using manufacturer wiring diagrams:

Verify:

Repair:

Stable power and ground are critical for maintaining uninterrupted Fuel Temperature Sensor operation.

Step 25 – Repair Intermittent Open or Short Circuits

Intermittent circuit faults may occur only under certain operating conditions.

Inspect for:

Move the harness during testing to duplicate the failure before completing repairs.

Step 26 – Verify Sensor Operation

After repairs:

Monitor live scan-tool data.

Verify:

Fuel Temperature Sensor “B” should provide consistent data throughout engine operation.

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

If equipped with multiple Fuel Temperature Sensors:

Compare:

Both sensors should report realistic temperatures based on their mounting locations.

Large intermittent 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 install the latest PCM calibration before replacing the control module.

Step 29 – Perform an Extended Road Test

Because intermittent faults may not appear immediately:

Drive the vehicle under multiple operating conditions:

Monitor live Fuel Temperature Sensor “B” data throughout the drive.

No signal interruptions or pending DTCs should occur.

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 P0189

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 an extended road test.
  7. Complete an OBD-II drive cycle.
  8. Verify no pending or permanent DTCs return.
  9. Perform a final scan confirming continuous Fuel Temperature Sensor “B” operation without signal interruptions.

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 P0189 repairs involve correcting intermittent 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 intermittent harness failures near frame-mounted wiring.

Chrysler, Dodge, Jeep, Ram

Inspect:

Heat cycling frequently contributes to intermittent connector failures.

Toyota/Lexus

Fuel Temperature Sensor “B” failures are relatively uncommon. Thoroughly inspect connectors, wiring movement, and terminal tension 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 P0189?

The most common repairs include replacing Fuel Temperature Sensor “B,” repairing intermittent wiring faults, replacing damaged connectors, repairing broken conductors, correcting intermittent shorts, updating PCM software, or replacing the Fuel Composition Sensor assembly if the sensor is integrated.

Can I drive with P0189?

Usually, yes. Most vehicles remain drivable, but intermittent sensor communication may reduce fuel economy, increase emissions, and occasionally affect engine performance until repairs are completed.

Does P0189 always mean Fuel Temperature Sensor “B” is bad?

No. Loose connectors, broken wiring, moisture intrusion, intermittent shorts, poor ground connections, and PCM software issues frequently trigger P0189 without complete sensor failure.

Can bad wiring trigger P0189?

Absolutely. Broken conductors, loose terminals, connector corrosion, harness movement, intermittent shorts, and damaged insulation are among the most common causes of P0189.

Is P0189 a serious code?

P0189 is generally considered a moderate severity diagnostic trouble code. While the vehicle is usually safe to drive, intermittent electrical faults typically worsen over time and can eventually lead to drivability problems, reduced fuel economy, and increased emissions.

Final Thoughts

The P0189 Fuel Temperature Sensor “B” Circuit Intermittent code indicates the PCM has detected an unstable or inconsistent electrical signal from Fuel Temperature Sensor “B”. In most cases, the root cause is a failing sensor, loose connector, damaged wiring, broken conductors, moisture intrusion, or intermittent short, 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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