What is the P0187 Code?
The P0187 error code is a generic powertrain code applicable to most vehicles equipped with the OBD-II standard (Toyota, Ford, Nissan, Fiat, Chevrolet, Dodge, etc.). It indicates that the Powertrain Control Module (PCM) has detected an abnormally low voltage signal from the Fuel Temperature Sensor B circuit.
Function of the Fuel Temperature Sensor
The fuel temperature sensor is often integrated with the fuel composition sensor. This assembly, located between the fuel tank and the injection rail, analyzes in real-time the composition (ethanol percentage, presence of water) and the temperature of the fuel.
It sends a signal to the PCM in the form of a square wave. The pulse width (horizontal part) corresponds to the temperature: the wider it is, the higher the temperature. If this value falls outside the expected range or is inconsistent (e.g., significantly lower than ambient temperature), the PCM records the P0187 code and may illuminate the Malfunction Indicator Lamp (MIL).
Severity and Symptoms of the P0187 Code
This code is considered severe because an incorrect fuel temperature skews the PCM’s calculations for injection and combustion, which can eventually damage the engine.
Symptoms may include:
- Illumination of the Malfunction Indicator Lamp (MIL)
- No obvious symptoms (the vehicle appears to operate normally)
- Presence of other codes related to fuel composition
- Possibility of rough idle or slight power loss
Possible Causes of the P0187 Code
Several failures can be the cause of this code:
- Faulty fuel temperature/composition sensor
- Faulty wiring (open circuit, short circuit, oxidized or damaged connectors)
- Poor sensor ground
- Problem with the PCM module (faulty module or programming error)
- Poor quality or heavily contaminated fuel
Diagnosis and Repair Procedures
⚠️ Important Tip: Always start by consulting your manufacturer’s Technical Service Bulletins (TSBs). It might be a known issue with a specific correction procedure.
Required Tools
- Advanced OBD-II scanner (with live data viewing)
- Digital Multimeter (DVOM)
- Oscilloscope (recommended for precise analysis)
- Infrared thermometer
- Technical documentation (e.g., AllData, Mitchell1)
Diagnostic Steps
- Visual Inspection: Carefully inspect the wiring and connectors associated with the sensor. Look for any signs of damage, corrosion, or burning.
- Electrical Test: Using the multimeter, check for the presence of the reference voltage (usually 5V) and ground at the sensor connector (engine off, ignition on).
- Sensor Test: If the power and ground are correct, use the oscilloscope to observe the sensor’s signal. Compare the temperature read by the scanner with a physical measurement taken with the infrared thermometer on the fuel line. A significant discrepancy indicates a faulty sensor.
- PCM Test: If the signal is absent at the sensor connector but present at the PCM, the problem lies in the wiring. If the signal is absent even at the PCM, the PCM is potentially faulty.
💡 Tip: After any repair, clear the codes and perform a drive cycle to verify that the code does not reappear and that the PCM enters the “ready” mode.
Conclusion and Call to Action
The P0187 code should not be ignored. Accurate diagnosis helps avoid costly repairs and ensures your engine’s performance and longevity.
Don’t feel comfortable with these procedures? Entrust the diagnosis to a professional mechanic equipped with the proper tools for a reliable diagnosis.