Code P0186: Fuel Temperature Sensor B Circuit Range/Performance
The error code P0186 is a generic powertrain code applicable to most OBD-II equipped vehicles (Nissan, Ford, Fiat, Chevrolet, Toyota, Dodge, etc.). It indicates that the Powertrain Control Module (PCM) has detected an abnormal voltage signal from the fuel temperature sensor B circuit, outside the expected operating range.
Role of the Fuel Temperature Sensor
The fuel temperature sensor is typically integrated with the fuel composition sensor. Located between the tank and the fuel rail, it measures both the fuel composition (ethanol content, water, contaminants) and its temperature. This data is essential for the PCM to accurately adjust fuel injection, especially on flex-fuel vehicles.
Symptoms of Code P0186
- No noticeable symptoms (asymptomatic in some cases)
- Illumination of the Malfunction Indicator Lamp (MIL)
- Possible presence of other codes related to fuel composition
- Abnormal air-fuel mixture affecting performance
Possible Causes
- Faulty fuel temperature/composition sensor
- Wiring issue: open circuit, short circuit, or damaged connectors
- PCM failure or programming error
- Faulty intake air temperature sensor
Diagnostic Procedures
Start by consulting the manufacturer’s Technical Service Bulletins (TSBs) to check if the issue is subject to a recall or specific procedure.
Recommended equipment: OBD2 scanner, digital multimeter (DVOM), oscilloscope, infrared thermometer.
- Visual Inspection: Check the condition of the connectors and wiring associated with the sensor. Look for any signs of corrosion, damage, or disconnection.
- Electrical Test: Using a multimeter, check for the presence of the reference voltage (5V) and ground at the sensor connector. No signal? Check the circuit up to the PCM.
- Sensor Test: Use an oscilloscope to analyze the sensor’s output signal. Compare the actual fuel temperature (measured with an infrared thermometer) with the value read by the scanner. A significant discrepancy indicates a faulty sensor.
- Resistance Test: Measure the sensor’s resistance (refer to manufacturer specifications). Remember to disconnect the connector before any measurement.
Repair and Tips
After any repair, clear the codes and perform a road test to ensure the fault does not reappear. If the PCM enters “ready” mode and the MIL does not come back on, the issue is resolved.
💡 Need help? Consult a professional equipped with advanced diagnostic tools for an accurate diagnosis, especially if you suspect a PCM failure.