What it means
Same as P04D2 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 while the EGR system operates. P04E9 sets when that signal changes erratically or drops in and out, rather than remaining consistently outside its expected range.
Common causes
Most likely first.
- Intermittent contact at connector
- Connector with intermittent contact under vibration
- Harness routed against vibrating component
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
- Review freeze-frame data and graph sensor D's live reading to see whether the signal jumps or briefly disappears under particular operating conditions.
- Inspect sensor D's connector for a loose fit, corrosion, damaged terminals, or signs of vibration-related movement.
- Check the wiring route for rubbing against vibrating parts, tension, or heat damage near the exhaust.
- With live data displayed, carefully move the accessible harness and connector to see whether the reading becomes erratic, following safe workshop practice around a running engine.
- Test continuity and connections in sensor D's circuit against the manufacturer's procedure, then check the sensor if the harness passes.
Common fixes
- Secure a loose sensor D connector and harness.
- Clean or repair terminals with intermittent contact.
- Repair or reroute wiring that rubs against a vibrating component or exhaust heat source.
- Replace sensor D if the circuit is stable but the sensor output remains erratic.
Can I keep driving?
If the fault comes and goes but the engine is otherwise smooth, limit driving to necessary short trips until it is diagnosed. Stop putting the engine under heavy load if knocking or hesitation develops, and do not ignore a worsening or persistent loss of power.
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.