P05C5

What it means

P05C5 means the engine control unit has seen the signal from the engine coolant pressure sensor circuit sit higher than its expected voltage range. This usually points to an electrical fault such as an open ground, a short to voltage or a failed sensor. It can also be set by a genuine over-pressure in the cooling system. Sensor location and the expected values vary by model and engine.

Symptoms

• Engine warning light on
• Coolant temperature or low coolant warning on the dash in some models
• Engine running hotter than normal or cooling fans running constantly
• Reduced power or limp mode on some models
• Coolant pressure reading stuck high or implausible in live data
• Other coolant system or thermal management codes stored

Possible causes

• Faulty coolant pressure sensor reading high internallylikely
• Open circuit in the sensor ground wire or a poor ground connectionlikely
• Signal wire shorted to a voltage supply or to the 5 volt referencepossible
• Corroded, loose or damaged sensor connector terminalspossible
• Genuine excess cooling system pressure from a faulty pressure cap, blocked flow or combustion gases entering the coolantpossible
• Fault inside the engine control unitrare

How to diagnose

1. Read all stored codes and the freeze frame data, noting engine temperature, load and speed when the fault set, and check for other coolant or sensor supply codes.
2. With the engine cold, check the coolant level and condition, and look for leaks, oil contamination or signs of overheating.
3. Inspect the sensor, its connector and the wiring back along the loom for chafing, corrosion, water ingress or heat damage.
4. Check live data of the coolant pressure reading with the engine cold and key on, and compare it to what you would expect from ambient pressure for that model.
5. Unplug the sensor and check the reference voltage, ground and signal wire against the manufacturer wiring diagram, looking for opens or shorts to voltage.
6. Pressure test the cooling system and the cap, and check for combustion gas in the coolant if pressure is genuinely high.
7. Check the sensor signal with a known-good sensor or against a mechanical pressure reading if the model allows it.
8. Clear the code and road test, then recheck live data to confirm the fault does not return.

How to fix

• Replace the coolant pressure sensor if it is faulty or reading high with correct wiring.
• Repair or replace damaged wiring, and clean or renew corroded connector terminals.
• Repair the ground or the short to voltage on the signal or reference circuit.
• Renew a faulty pressure cap or clear any restriction causing genuine over-pressure.
• Repair the cause of combustion gas entering the coolant, such as a head gasket or cracked head, if confirmed.
• Replace or reprogram the engine control unit only if all wiring and the sensor test good and the manufacturer confirms a fault.

Can I keep driving?

Nearby codes

• P05C4GenericEngine Coolant Pressure Sensor Circuit Low
• P05C6GenericEngine Coolant Pressure Sensor Circuit Intermittent/Erratic