P0540: Intake Air Heater A Circuit
What to do
Driveable, and you may notice nothing at all until cold weather. Expect harder starting and white smoke on frosty mornings. Worth fixing before winter rather than during it.
What this code means
A circuit fault on the intake air heater. Diesels that use a grid heater rather than individual glow plugs warm the incoming air electrically for the first moments of a cold start, which makes the charge hot enough to ignite reliably and cuts the white smoke and clatter of a cold diesel.
It draws a very large current — often more than the starter's own accessories — so it is switched by a heavy relay, and the failure is at least as often that relay or its heavy cabling as the element itself. The symptom is entirely seasonal: nothing whatsoever in summer, and difficult cold starts with white smoke the first frosty morning.
Likely causes
Start here
- Failed intake air heater relay · easy
- Failed intake air heater element · moderate
- Corroded or loose connector · easy
Less common
- Corroded heavy supply cable · moderate
Symptoms
Components involved
Information, not instruction
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Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
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