P1255 is a manufacturer-specific OBD-II diagnostic trouble code. Because it is manufacturer-specific, its exact definition depends on the vehicle application, most commonly relating to the engine coolant temperature sensor circuit.
The exact application must be verified before diagnosis. The code indicates a detected high voltage or intermittent condition in the coolant sensor circuit, but testing is required to identify the root cause.
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Key Takeaways
- P1255 is a manufacturer-specific code, meaning its exact definition varies by automaker and vehicle application.
- On many General Motors applications, it indicates an intermittent high voltage condition in the Engine Coolant Temperature (ECT) sensor circuit.
- On certain Volkswagen and Audi applications, it indicates a short to positive or open circuit in the secondary coolant temperature sensor.
- Diagnosis requires verifying the exact factory definition and testing the relevant sensor circuits, wiring, and connectors.
P1255 Code Description and Implications
P1255 is a manufacturer-specific powertrain code. Because the second digit is “1”, the definition is controlled by the automaker rather than the SAE standardized list.
Some General Motors applications: P1255 indicates an intermittent high voltage or high input condition in the Engine Coolant Temperature (ECT) sensor circuit.
Certain Volkswagen and Audi applications: P1255 indicates a short to positive or an open circuit in the Engine Coolant Temperature Sensor 2 (G62).
When the control module detects a signal voltage that exceeds the normal operating range or drops out intermittently, it sets this fault code. Because this is a manufacturer-specific code, the exact definition and diagnostic steps vary by automaker.
Common Causes of the P1255 Code
Possible causes depend entirely on the specific vehicle application.
For ECT sensor circuits, an open circuit, a short to voltage in the signal wire, or a failing sensor can cause a high voltage signal.
Damaged wiring, chafed harnesses, or corroded connectors are frequent culprits for intermittent signal dropouts.
In some cases, low engine coolant levels or air pockets in the cooling system can cause erratic temperature readings, though this typically sets different correlation codes.
Symptoms Associated With P1255
The primary symptom is an illuminated check engine light.
Drivers may experience poor fuel economy, rough idling, or incorrect transmission shift points if the control module receives inaccurate coolant temperature data.
The cooling fans may run continuously or fail to turn on, depending on how the control module interprets the faulty high-voltage signal.
Diagnosing the P1255 Trouble Code
Diagnosis must begin by confirming the exact factory definition for the specific make, model, and year.
Technicians inspect the ECT sensor wiring harness for opens, shorts to voltage, or corrosion.
Live data is monitored to compare the reported coolant temperature against ambient temperature or a known-good infrared thermometer reading.
The sensor’s resistance and signal voltage are tested and compared to the manufacturer’s specifications.
Repairing the P1255 Issue
Repairs follow the confirmed diagnosis for the specific application.
If wiring damage or a short to voltage is found, repairing the harness resolves the electrical fault.
If the ECT sensor fails the live data and electrical tests, replacing the confirmed failed sensor is required.
If the cooling system is low, repairing leaks and bleeding the system restores proper sensor contact with the coolant.
Cost Considerations for P1255 Repairs
Repair costs vary depending on the underlying fault and the vehicle application.
Replacing an engine coolant temperature sensor involves standard parts and minimal labor.
If the repair requires extensive wiring harness repair, labor costs increase.
Cost depends on diagnostic time, component accessibility, required parts, programming requirements, and labor.
Prevention Strategies for Future Occurrences
Inspecting exposed engine bay wiring harnesses can help identify developing damage from heat, vibration, or rodent activity.
Keeping electrical connectors clean and ensuring their weather seals are intact helps prevent moisture intrusion and corrosion.
Troubleshooting Tips and Best Practices
Never assume a manufacturer-specific code has a universal meaning. Always verify the exact factory service information for your specific vehicle.
Do not replace the ECT sensor without first verifying the wiring, connectors, and live data signal for intermittent high voltage.
If P1255 is accompanied by other sensor circuit high codes, suspect a shared 5-volt reference circuit issue or a common ground fault.
While this code relates to the cooling system, severe engine overheating from ignored cooling faults can cause widespread damage to engine components, and while not directly related to the fuel pump, cooling system failures should be addressed immediately to protect the entire engine.
More OBD-II Codes
| P1110 | P1111 | P1112 | P1114 |
| P1115 | P1116 | P1251 | P1252 |
| P1253 | P1254 | P1256 | P1257 |
| P1258 | P1259 | P1260 | P1261 |
| P0117 | P0118 | P1117 | P1118 |
| P1119 | P1120 | P1103 | P1104 |
Frequently Asked Questions
Is P1255 a generic OBD-II code?
No. P1255 is a manufacturer-specific code, meaning its exact definition and diagnostic procedure depend entirely on the vehicle’s make, model, and application.
Can I drive my vehicle with a P1255 code?
It depends on the application. If the faulty coolant sensor causes the cooling fans to fail or the engine to run poorly, driving the vehicle may cause severe overheating and should be avoided.
Will a P1255 code cause my cooling fans to run constantly?
Yes. On many applications, if the control module sees an erratic or high-voltage signal from the coolant sensor, it will command the cooling fans to run continuously as a fail-safe measure.
Does P1255 always mean the coolant temperature sensor is broken?
No. The code often points to an electrical fault like damaged wiring, a short to voltage, or a corroded connector rather than a failed sensor.
How do I clear a manufacturer-specific P1255 code?
Clearing the code requires fixing the underlying electrical or component fault. Simply using a scan tool to erase the code will not repair the root cause.
What Should You Do About the P1255 Code?
Confirm the exact factory definition for your specific vehicle, then follow the applicable manufacturer diagnostic procedure for the relevant system and components.
Because P1255 is manufacturer-specific, testing the exact wiring circuits, sensors, or connectors identified by the factory service information is required to find the root cause.
Once the fault is confirmed, perform the necessary repairs and verify the fix by clearing the codes and completing a test drive.
