What it means
EGR temperature sensor A above upper plausibility — open signal or short to B+. 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 A measures the temperature of exhaust gas in the EGR path. P040D sets when its signal is higher than the expected circuit range, often because the signal wire is open or shorted to a power source.
Common causes
Most likely first.
- Open signal line
- 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
- Record freeze-frame data and compare sensor A's live reading with other temperature readings to confirm whether the high signal is persistent.
- Inspect sensor A's connector and harness for a disconnected terminal, broken wire, corrosion, or insulation damage near a power source.
- With the wiring diagram, check the signal circuit for an open and for a short to battery voltage.
- Check sensor A's reference and ground circuits, then observe whether its reading responds as the EGR path warms.
- Test the sensor and circuit against the manufacturer's specification to separate a sensor fault from an open or shorted wire.
Common fixes
- Reconnect or clean a loose or corroded sensor A connector.
- Repair an open signal wire or wiring shorted to a power source.
- Replace EGR temperature sensor A if it fails the manufacturer's specification.
- Correct an EGR flow or cooler fault if actual temperature behavior remains implausible.
Can I keep driving?
If the engine runs normally, a short drive may be possible, but avoid heavy acceleration if it knocks or hesitates. The incorrect temperature feedback can disrupt EGR control and increase emissions; stop if loss of power makes driving unsafe.
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.