P05C4

What it means

P05C4 means the engine control unit has detected the signal from the engine coolant pressure sensor circuit is lower than the expected range. The ECU monitors the sensor's voltage and sets the code when it stays too low, which usually points to a short to earth, an open circuit, a lost supply or a faulty sensor. The fitment of this sensor and how it is used varies by make, model and engine.

Symptoms

• Engine warning light on
• Possible reduced power or limp mode on some vehicles
• Coolant temperature or cooling fan behaviour that seems abnormal
• Possible low coolant warning or coolant pressure warning on the dash
• Other stored codes relating to cooling or sensor supply voltage

Possible causes

• Faulty engine coolant pressure sensor reading low or failed internallylikely
• Damaged, chafed or shorted-to-earth signal wire in the sensor harnesslikely
• Corroded, loose or contaminated sensor connector terminals, or coolant ingress in the pluglikely
• Open circuit or poor connection on the sensor 5 volt reference supply or earthpossible
• Genuinely low coolant pressure caused by a coolant leak, low coolant level or a faulty cap or pumppossible
• Fault inside the engine control unitrare

How to diagnose

1. Read all stored and pending codes and note the freeze frame data, including coolant temperature and engine load when the fault set
2. Check the coolant level when cold and look for external leaks, a damaged cap or signs of coolant loss
3. Inspect the sensor, its connector and the wiring for damage, chafing, corrosion, moisture or coolant contamination
4. Using live data, compare the reported coolant pressure with expected values at key-on and with the engine running; check the model-specific specification
5. With the connector unplugged, measure the reference supply voltage and earth at the sensor against the manufacturer wiring information
6. Check the signal wire for a short to earth and for continuity back to the ECU with the ignition off
7. Check whether any other sensors sharing the same reference supply have set codes, which would point to a wiring or ECU supply fault
8. If the wiring and supply are good, test or substitute the sensor following the manufacturer's procedure

How to fix

• Replace the engine coolant pressure sensor if it is confirmed faulty
• Repair or replace damaged wiring and clean or renew corroded connector terminals
• Restore the supply or earth circuit where an open circuit or high resistance is found
• Repair any coolant leak, top up with the correct coolant and bleed the system as specified
• Replace a faulty pressure cap or other cooling system component if it is causing low pressure
• Clear the codes after repair and road test to confirm the fault does not return

Can I keep driving?

Nearby codes

• P05C3GenericEngine Coolant Pressure Sensor Circuit Range/Performance
• P05C5GenericEngine Coolant Pressure Sensor Circuit High