P1185

What Does Code P1185 Mean?

DTC P1185 signifies a fault within the Fuel Pump Temperature Sensor (FTS) circuit, specifically indicating an excessively high temperature reading from the sensor. The Engine Control Module (ECM), also known as the Powertrain Control Module (PCM), monitors the electrical signal from the FTS to determine the temperature of the fuel within the fuel tank or the fuel pump assembly itself. The FTS is typically a Negative Temperature Coefficient (NTC) thermistor, meaning its electrical resistance decreases as the fuel temperature increases. The ECM supplies a reference voltage (typically 5V) to the sensor and measures the voltage drop across it. When the ECM detects a signal voltage from the FTS that corresponds to a temperature exceeding a calibrated maximum threshold, or a signal voltage that is implausibly low (indicating very low resistance, hence high temperature, for an NTC type), it will store the P1185 code and illuminate the Malfunction Indicator Lamp (MIL). This condition suggests either an actual severe overheating of the fuel pump or fuel, or more commonly, an electrical circuit fault that mimics such a condition.

Common Symptoms

• Malfunction Indicator Lamp (MIL) Illumination: The “Check Engine” light will be illuminated on the dashboard.
• Reduced Fuel Economy: If the ECM adjusts fuel trim or pump operation based on the incorrect temperature reading.
• Poor Engine Performance: Possible hesitation, rough idle, or a general lack of power if fuel delivery or pressure is compromised due to ECM’s failsafe strategies.
• Hard Starting or No-Start Condition: In severe cases, especially if fuel pressure regulation is affected.
• Increased Fuel Pump Noise: Could be a symptom of an actual overheating fuel pump, though often this code indicates an electrical issue.
• No Discernible Symptoms: In some instances, the vehicle may appear to run normally, with only the MIL illuminated, as the ECM might operate the fuel system using default values or other sensor inputs.

What Causes the Code P1185?

• Faulty Fuel Pump Temperature Sensor (FTS): The sensor itself may have an internal short or have degraded, causing it to report an inaccurately low resistance value (interpreted as high temperature) to the ECM.
• Wiring Harness Issues: A short to ground in the FTS signal wire, an open circuit, or excessive resistance within the wiring harness leading to or from the sensor.
• Corroded or Damaged Electrical Connectors: Poor connection at the FTS or ECM due to corrosion, bent pins, or loose terminals can lead to intermittent or incorrect signal transmission.
• Actual Fuel Pump Overheating: A failing fuel pump drawing excessive current can genuinely overheat the fuel in the tank, causing the FTS to accurately report an out-of-range high temperature. This would indicate a failing fuel pump module rather than a sensor fault.
• ECM/PCM Malfunction: Although rare, a fault within the ECM’s internal FTS input circuit could lead to misinterpretation of the sensor signal.

How to Diagnose and Troubleshoot

A systematic approach is crucial for diagnosing P1185:

1. Retrieve and Analyze Freeze Frame Data: Connect an OBD-II scanner to extract the P1185 code and any associated freeze frame data. Note engine operating conditions (RPM, engine load, coolant temperature, vehicle speed) when the code was set. This provides context for the fault.
2. Monitor Live Data: Using the OBD-II scanner, observe the live data stream for the Fuel Pump Temperature Sensor (FTS) reading. Compare the FTS reading to other temperature sensors (e.g., Intake Air Temperature, Engine Coolant Temperature) when the engine is cold soaked. An extremely high or static FTS reading, inconsistent with ambient or engine temperatures, indicates a sensor or circuit fault. If the FTS reports a plausibly high temperature that aligns with engine operating conditions (e.g., after prolonged high-load operation), further investigation into actual fuel pump overheating may be warranted.
3. Visual Inspection of Wiring and Connectors: Disconnect the battery. Carefully inspect the FTS wiring harness for any signs of physical damage, chafing, cuts, or pinches, especially where it routes through the vehicle chassis or near hot components. Check the FTS electrical connector and the corresponding ECM connector for corrosion, bent pins, loose terminals, or moisture intrusion. Address any visible damage before proceeding.
4. Digital Multimeter (DMM) Testing – Sensor Resistance:
   • Locate and disconnect the FTS electrical connector, typically found on the fuel pump module within the fuel tank.
   • Using a DMM set to ohms, measure the resistance across the two terminals of the FTS itself.
   • Compare this reading to manufacturer specifications (often provided in a resistance-temperature chart). For an NTC thermistor, a reading significantly lower than expected for the ambient temperature, or near zero ohms, suggests an internal short within the sensor, consistent with a high-temperature reading.
5. Digital Multimeter (DMM) Testing – Circuit Integrity:
   • Reference Voltage: With the FTS disconnected, key in the ON position (engine off), use the DMM to measure voltage between the reference voltage wire at the harness connector and chassis ground. You should typically see around 5V. If not, troubleshoot the reference voltage circuit from the ECM.
   • Signal Circuit Voltage: With the FTS connected and key ON (engine off), backprobe the FTS signal wire at the sensor connector (or ECM connector if more accessible). The voltage reading will vary based on temperature. For an NTC thermistor indicating high temperature (low resistance), the signal voltage will be lower than normal, potentially near 0V.
   • Continuity and Shorts: With the battery disconnected and the ECM connector disconnected, use the DMM to check for continuity between the FTS signal wire and its corresponding pin at the ECM connector. Check for shorts to ground (resistance between signal wire and chassis ground should be infinite) and shorts to voltage (check for battery voltage on the signal wire with the key ON, if the harness is plugged into the ECM, this is for detecting short to power, but better done with harness unplugged from ECM and checking for continuity to power lines if relevant).
6. Actual Fuel Pump Current Draw (If Actual Overheating Suspected): Use an inductive amp clamp to measure the current draw of the fuel pump. Excessive current draw can indicate a failing pump, which would generate more heat. Compare to manufacturer specifications.

Recommended Repairs and Solutions

The corrective action for P1185 depends on the diagnostic findings:

• Repair or Replace Wiring/Connectors: If the visual inspection or DMM tests reveal damaged, corroded, or open circuits in the wiring harness or connectors, perform professional repairs. Use appropriate wiring repair kits, solder and heat shrink tubing for open circuits, and terminal repair kits for corroded or damaged connector pins. Always ensure secure and weather-tight connections.
• Replace the Fuel Pump Temperature Sensor (FTS): If the DMM resistance test confirms the FTS itself is faulty (e.g., internal short, out of specified resistance range). In many modern fuel delivery systems, the FTS is an integral part of the complete fuel pump module and may not be serviceable separately. In such cases, the entire fuel pump module would need replacement.
• Replace the Fuel Pump Module: If diagnostics indicate the FTS is integrated and non-serviceable, or if the actual fuel pump is found to be drawing excessive current and causing genuine overheating, the entire fuel pump module inside the fuel tank will need to be replaced. This is a common repair for P1185, as the sensor often fails within the assembly.
• ECM/PCM Replacement/Reprogramming: This is a last resort and should only be considered after all other possibilities have been meticulously ruled out. If an ECM failure is suspected, it usually requires specialized programming and calibration after installation.
• Clear DTCs and Test Drive: After any repair, clear the stored diagnostic trouble codes using an OBD-II scanner. Perform an extended test drive under various operating conditions to confirm the repair and ensure the P1185 code does not return. Continuously monitor the FTS live data during the test drive to verify correct operation.