Fuel Temperature Sensor B Circuit Low Input
P0187 indicates the fuel temperature sensor B circuit is reading abnormally low voltage, preventing the engine computer from accurately measuring fuel temperature. This is critical for flex-fuel vehicles that rely on fuel temperature data to calculate proper fuel delivery and ignition timing strategies.
What You Might Notice
- Check Engine Light (MIL) illumination
- Reduced fuel economy
- Engine hesitation or rough idle
- Difficulty starting, especially in cold weather
- Possible limp mode activation
Most Common Causes
- 1
Faulty fuel temperature sensor B
The sensor itself has failed or is stuck reading low, sending incorrect voltage signals to the PCM. This is the most common cause of this code.
- 2
Damaged sensor wiring or connector
Open circuit, loose connector, or corroded pins in the fuel temperature sensor B circuit can cause low voltage readings.
- 3
PCM or ECU malfunction
A defective powertrain control module may not properly interpret sensor signals, though this is less common than sensor failure.
- 4
Fuel composition sensor failure
On flex-fuel vehicles, other fuel composition sensors may also fail simultaneously, affecting the vehicle's fuel calculation strategy.
How to Diagnose It
- 1
Check Faulty fuel temperature sensor B — The sensor itself has failed or is stuck reading low, sending incorrect voltage signals to the PCM. This is the most common cause of this code.
- 2
Check Damaged sensor wiring or connector — Open circuit, loose connector, or corroded pins in the fuel temperature sensor B circuit can cause low voltage readings.
- 3
Check PCM or ECU malfunction — A defective powertrain control module may not properly interpret sensor signals, though this is less common than sensor failure.
- 4
Check Fuel composition sensor failure — On flex-fuel vehicles, other fuel composition sensors may also fail simultaneously, affecting the vehicle's fuel calculation strategy.
How to Fix It
- 1
Replace fuel temperature sensor B
Locate and remove the faulty fuel temperature sensor B (typically in the fuel tank or fuel line), and install a new OEM or quality aftermarket sensor to restore accurate temperature readings.
- 2
Repair or replace sensor wiring and connectors
Inspect the sensor circuit wiring for damage, corrosion, or loose connections. Repair any damaged wire segments or replace corroded connectors to restore proper electrical continuity.
- 3
Check fuel pump and fuel system voltage
Verify the fuel pump relay and power supply to the sensor circuit are functioning correctly by testing voltage at the sensor connector with a multimeter.
- 4
Clear code and retest after repairs
After completing repairs, use a diagnostic scanner to clear the fault code and perform a road test to ensure the code does not return and vehicle operates normally.
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