What it means
Same as P04D1 on EGR temperature sensor D. EGR mixes inert exhaust into intake to lower combustion peak temperature — too little raises NOx, too much causes misfires and rough running.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
EGR temperature sensor D reports exhaust temperature to the control module for EGR monitoring. P04E8 sets when its signal is higher than expected, often because the signal wire is shorted to a supply voltage or the circuit connection is faulty.
Common causes
Most likely first.
- Signal shorted to supply
- Connector pins corroded - high contact resistance
- Supply wire pinched against B+ source
Symptoms
- Check engine light on
- Pinging or knocking under load
- Power loss and hesitation
- Possible rough idle
- Failed emissions inspection (NOx)
How to diagnose it
- Check freeze-frame data and sensor D's live reading for an implausibly high or fixed value, noting engine temperature and operating conditions when the code set.
- Inspect sensor D's connector for corrosion, displaced pins, or a poor fit that could disrupt the signal.
- Trace the sensor D harness for pinching or insulation damage where the signal wire could touch a power source.
- Test the signal circuit for a short to supply voltage using the manufacturer's procedure.
- If the circuit is intact, test sensor D against the manufacturer's specification to determine whether the sensor itself is faulty.
Common fixes
- Reconnect and secure sensor D's connector.
- Repair corroded or damaged connector terminals.
- Repair the signal wire where it is pinched or contacting a supply source.
- Replace sensor D if its output fails the manufacturer's specification.
Can I keep driving?
A short, gentle drive is generally reasonable if the engine runs smoothly and does not knock severely. Avoid heavy load if pinging or hesitation occurs, and arrange repair soon because incorrect EGR temperature feedback can affect drivability and emissions.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.