P04D2
EGR Temperature Sensor C Circuit Intermittent/Erratic.
- Generic
- Powertrain
- Generic code
- Medium severity
How this code is built
- P
- SystemPowertrain
- 0
- Defined bySAE, the same on every car
- 4
- AreaAuxiliary emission controls
- D2
- FaultThe specific fault in that area
What it means
P04D2 means the engine control unit has detected an intermittent or erratic signal from EGR temperature sensor 'C' circuit. The signal voltage jumps, drops out or changes in a way that does not match real exhaust gas temperature changes. Which physical sensor is 'C' depends on the vehicle and engine, so check the manufacturer's data for the model.
Symptoms
- Engine management light on
- Possible reduced performance or limp mode on some models
- Rough idle or hesitation if EGR operation is affected
- Slightly higher fuel consumption
- Failed emissions test
- Other EGR-related codes stored alongside
Possible causes
- Loose, corroded or damaged connector at the EGR temperature sensorlikely
- Chafed, broken or heat-damaged wiring causing intermittent open or short circuitlikely
- Failing EGR temperature sensor giving erratic readingslikely
- Heavy carbon build-up on the sensor or in the EGR cooler or pipework affecting readingspossible
- Poor sensor reference or earth supply from a shared circuit faultpossible
- Internal fault in the engine control unitrare
How to diagnose
- Read all stored and pending codes and note the freeze frame data, including engine temperature, load and speed when the fault set.
- Check for related EGR, exhaust temperature or sensor supply codes, and look up any manufacturer service bulletins for the model.
- Visually inspect the sensor, connector and wiring for heat damage, chafing, corrosion, water ingress and loose pins.
- With the engine running, view the live EGR temperature reading and gently wiggle the harness and connector to see if the value jumps or drops out.
- Compare the live reading with other temperature data when the engine is cold, and watch how it rises as the engine warms and EGR operates.
- Test the sensor circuit for supply, signal and earth continuity and for shorts to earth or voltage, using the manufacturer's wiring diagram.
- Measure the sensor resistance against the specification for the model, if one is published.
- Inspect the sensor tip and EGR passages for heavy carbon deposits.
How to fix
- Clean, repair or replace the damaged connector terminals and secure the connector properly.
- Repair or replace damaged wiring sections, and re-route and secure the harness away from heat and movement.
- Replace the EGR temperature sensor if it reads erratically or is out of specification.
- Clean or replace carbon-fouled EGR components as the manufacturer advises.
- Clear the code after repair and road test to confirm it does not return.
Can I keep driving?
Medium severity
The car can usually be driven for a short time, but book it in soon as EGR control may be affected and the problem could worsen. If the car enters limp mode or runs badly, limit driving until it is checked.
Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.