P0540low severityPowertrain
Intake Air Heater Circuit
on 2009 Audi A8 4.2L V8 · AWD
What this code means
The PCM detects a fault in the intake air heater circuit. This heater warms incoming air to help cold starting, common on diesels.
Symptoms
- Hard cold starts
- Rough running when cold
- Check engine light on
Common causes
- Faulty intake air heater
- Wiring or connector faults
- Blown fuse or relay
- Faulty control module
Diagnostic steps
- Retrieve trouble codes
- Inspect heater wiring and relay
- Test heater element resistance
- Check for power at heater
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16515
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