A faulty coolant pressure sensor with an internal intermittent connection.; Damaged or chafed wiring in the sensor circuit, especially near hot or moving components.; Corroded or loose electrical connector pins at the sensor or ECM.; Poor ground connection for the sensor return circuit.; Coolant contamination or air pockets causing erratic pressure readings at the sensor.; A failing ECM driver circuit, though this is less common.

DTC codes / P05xx · Vehicle speed, idle control and auxiliary inputs / P05C6

P05C6Engine Coolant Pressure Sensor Circuit Intermittent/Erratic

Q: What does code P05C6 mean?

Engine Coolant Pressure Sensor Circuit Intermittent/Erratic. P05C6 indicates that the engine control module (ECM) has detected an intermittent or erratic signal from the engine coolant pressure sensor circuit, meaning the voltage readings are jumping around or dropping out rather than staying steady. The ECM sets this code when the signal does not match expected values for a given operating condition over a period of time.

P05C6 indicates that the engine control module (ECM) has detected an intermittent or erratic signal from the engine coolant pressure sensor circuit, meaning the voltage readings are jumping around or dropping out rather than staying steady. The ECM sets this code when the signal does not match expected values for a given operating condition over a period of time.

SystemPowertrain

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyIntermediate

AreaVehicle speed, idle control and auxiliary inputs

Symptoms you may notice

Illumination of the check engine light, often with no other noticeable symptoms.
Intermittent coolant temperature gauge fluctuation or warning messages.
Reduced engine performance or power derating if the ECM enters a protection mode.
Possible overheating if the sensor fault masks a real low-coolant-pressure condition.
Erratic cooling fan operation as the ECM misinterprets pressure data.
A stored freeze-frame showing the fault occurred under specific load or temperature conditions.

Common causes, most likely first

A faulty coolant pressure sensor with an internal intermittent connection.
Damaged or chafed wiring in the sensor circuit, especially near hot or moving components.
Corroded or loose electrical connector pins at the sensor or ECM.
Poor ground connection for the sensor return circuit.
Coolant contamination or air pockets causing erratic pressure readings at the sensor.
A failing ECM driver circuit, though this is less common.

How to diagnose and fix it

Perform a visual inspection of the sensor, connector, and wiring for obvious damage or corrosion.
Use a scan tool to monitor live coolant pressure sensor voltage while wiggling the harness and connectors to catch intermittent faults.
Check the sensor reference voltage and ground at the connector with a multimeter, comparing to manufacturer specifications.
Test the sensor resistance or voltage output with a pressure gauge and compare to a known-good sensor.
Repair or replace any damaged wiring, terminals, or connectors, then clear the code and verify the repair.
If the sensor is faulty, replace it and bleed the cooling system properly to remove air pockets.
As a last resort, diagnose the ECM circuit or replace the ECM if all other possibilities are ruled out.

Intermittent faults hide in plain sight

A loose ground or chafed wire often causes this code only when the engine is hot or vibrating, so a cold static test may pass.
The coolant pressure sensor is sometimes integrated into the expansion tank or radiator, making replacement more involved than a simple screw-in sensor.
Air pockets in the cooling system can create pressure spikes that mimic a faulty sensor, so always bleed the system after any coolant work.
This code can be set by a low coolant level or a failing water pump that causes pressure fluctuations, not just an electrical fault.
Do not replace the sensor without checking the connector pins for fretting corrosion, which is a common cause of intermittent signals.

Can I keep driving with P05C6?

You can usually drive with this code if the engine temperature gauge reads normal and there are no overheating symptoms, but avoid heavy loads or long trips until it is diagnosed. If the temperature gauge fluctuates or the engine overheats, stop driving and have the vehicle towed to prevent engine damage.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.