P04D0

What it means

P04D0 means the engine control unit has detected a low voltage or signal in the circuit of exhaust gas recirculation (EGR) temperature sensor 'C'. The signal sits below the expected range, which usually points to a short to earth, a wiring fault or a failed sensor. Which sensor is 'C' and where it sits in the EGR system depends on the vehicle and engine, so check the manufacturer's information.

Symptoms

• Engine warning light on
• Possible reduced performance or limp mode on some vehicles
• Rough running or hesitation at light load
• Increased emissions or smoky exhaust on some engines
• Other EGR-related fault codes stored alongside

Possible causes

• Signal wire chafed and shorted to earth or to another low-voltage circuitlikely
• Faulty EGR temperature sensor with an internal shortlikely
• Corroded, damaged or contaminated connector or terminals at the sensorpossible
• Heat damage to the wiring or sensor plug close to the EGR cooler or exhaustpossible
• Water or soot ingress into the sensor or connectorpossible
• Fault in the engine control unit sensor inputrare

How to diagnose

1. Read all stored codes and freeze frame data, noting engine temperature, load and speed when the fault set, and check for related EGR codes
2. Look up which sensor is 'C' on this model and where it is fitted, using manufacturer data
3. Inspect the sensor, wiring and connector for heat damage, chafing, corrosion, water or soot contamination
4. View live data for the EGR temperature reading and compare it with coolant or intake air temperature on a cold engine; an implausibly low or fixed reading suggests a fault
5. Unplug the sensor and check the live reading or signal voltage; a change to the open-circuit value suggests a sensor fault rather than a wiring short
6. Test the signal wire for a short to earth and the reference supply and earth for continuity, following the wiring diagram
7. Measure the sensor resistance at a known temperature and compare it with the manufacturer's specification
8. Clear the code and road test to see whether it returns, rechecking live data

How to fix

• Repair or replace the shorted or damaged wiring section
• Replace the EGR temperature sensor if it fails resistance or live data checks
• Clean, repair or replace corroded or damaged connector terminals and secure the harness away from heat
• Fix the source of water or soot ingress, then replace the affected connector or sensor
• Replace or repair the engine control unit only after wiring and sensor faults are ruled out and the fault is confirmed

Can I keep driving?

Nearby codes

• P04CFGenericEGR Temperature Sensor C Circuit Range/Performance
• P04D1GenericEGR Temperature Sensor C Circuit High