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DTC codes / P01xx · Fuel and air metering / P0186

P0186Fuel Temperature Sensor B Circuit Range/Performance

P0186 indicates that the powertrain control module (PCM) has detected an abnormal signal from Fuel Temperature Sensor B, which is typically a second temperature sensor in the fuel system. The PCM compares the sensor's voltage or resistance against expected values for the current operating conditions and flags the circuit as out of range or performing erratically.

SystemPowertrain
Code typeGeneric (all makes)
SeverityLow
Fix difficultyIntermediate
AreaFuel and air metering

Symptoms you may notice

  • Illuminated check engine light, often with no other noticeable symptoms
  • Rough idle or hesitation when the engine is cold or during regeneration events
  • Reduced fuel economy or slightly elevated exhaust temperatures
  • Intermittent stalling or hard starting in extreme ambient temperatures
  • A stored freeze-frame showing fuel temperature readings that are implausible or stuck

Common causes, most likely first

  1. Faulty fuel temperature sensor B (internal short or open circuit)
  2. Damaged or corroded wiring harness or connector at the sensor
  3. Poor electrical ground or reference voltage supply to the sensor circuit
  4. Contaminated or degraded fuel affecting sensor response
  5. PCM software calibration issue or internal driver fault
  6. Aftermarket fuel system modifications that alter sensor placement or signal

How to diagnose and fix it

  1. Scan all modules and record freeze-frame data for fuel temperature sensor B
  2. Visually inspect the sensor connector and wiring for chafing, corrosion, or loose pins
  3. Measure sensor resistance or voltage at the connector and compare to manufacturer specifications
  4. Check reference voltage and ground integrity at the sensor harness with a multimeter
  5. Substitute a known-good sensor or simulate the signal with a resistor box to confirm the fault
  6. Repair or replace damaged wiring, terminals, or the sensor as indicated by test results
  7. Clear codes and perform a road test to verify the repair and ensure no pending codes return

Fuel temperature sensor B diagnostic traps

  • Many technicians replace the sensor first, but a chafed harness near the fuel tank or engine mount is a more common root cause than sensor failure itself.
  • A stuck or biased sensor can pass a simple resistance check at room temperature yet fail only when fuel warms up, so testing must include a heat soak or live data drive.
  • P0186 can be set by a PCM calibration that misinterprets a normal sensor signal during cold-start enrichment, so check for technical service bulletins before condemning parts.
  • Fuel temperature sensor B is often part of a combined fuel pressure and temperature sensor assembly, meaning the entire unit may need replacement even if only the thermistor is faulty.
  • Codes for fuel pressure or fuel rail temperature may accompany P0186, and diagnosing those first can reveal that the temperature fault is a secondary effect of a pressure problem.

Can I keep driving with P0186?

The vehicle is generally safe to drive with P0186 because the PCM substitutes a default fuel temperature value, but avoid heavy towing or sustained high-load operation until the fault is repaired. Prolonged driving with an erratic sensor can affect fuel economy and emissions, so schedule diagnosis soon.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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