Fuel and air

P0187 — Fuel Temperature Sensor 'B' Circuit Low Input

Severity: medium Drive with care, to a shop

What P0187 means

The ECM sends a reference voltage to the fuel temperature sensor and reads the voltage change to work out fuel temperature. P0187 sets when the signal in the 'B' sensor circuit stays below the expected range. This usually points to a signal wire shorted to ground or a failed sensor. Fuel temperature is used to correct for fuel density and adjust fueling.

Symptoms

  • Check Engine light on
  • Hesitation or reduced power
  • Higher fuel consumption
  • Rough idle or occasional stalling
  • Hard starting

Possible causes

  1. Failed fuel temperature sensor 'B'
  2. Signal wire shorted to ground from damaged insulation
  3. Corroded, wet or damaged sensor connector
  4. Open circuit, poor connection or bad ground in the harness
  5. Rarely, an ECM fault or software problem

How to diagnose

  1. Scan for all codes and freeze frame data, clear the code and see if it returns
  2. Read the fuel temperature value on a scan tool and compare it with the actual temperature on a cold engine
  3. Inspect the sensor connector and harness for chafing, corrosion, moisture or damage
  4. Unplug the sensor: if the reading changes to an open-circuit value, suspect the sensor; if the low signal stays, look for a short in the wiring
  5. Check reference voltage (typically about 5 V) and ground at the connector with a multimeter
  6. Test the signal wire for a short to ground and for continuity to the ECM
  7. Measure sensor resistance and compare it with the spec for your vehicle
  8. Consider the ECM only after the sensor and wiring are cleared

Common fixes

  • Replace fuel temperature sensor 'B'
  • Repair or replace the damaged wiring and connector
  • Clean the terminals and restore a good ground
  • Update software or replace the ECM (rare)

Questions and answers

Can I drive with a P0187 code?

For a short time usually yes, but you may notice hesitation, worse fuel economy and hard starts. Have it diagnosed soon.

What most often causes P0187?

Most often it's the fuel temperature sensor itself or a short to ground in its wiring or connector. Start with a visual inspection of the harness and plug.

Is clearing the code enough?

No. If the cause remains, the code will come back. Find the fault in the sensor or wiring first.

This is general information about the code. The meaning can differ between makes and models: a scan tool and the repair manual for your car will show the exact cause.