P0540 to P0543 and P0640: diesel intake air heater
The heater that warms the air entering a diesel engine, or its control circuit, has a fault: the circuit is open, low or high.
SeverityLowLittle risk to the car, but the fault stays until it is repaired.
Can you keep driving?Safe to drive, book a checkWhat does P0540 mean?
Some diesel engines, often in pick-ups and commercial vehicles, warm the incoming air with an electric heating grid in the intake instead of, or as well as, glow plugs. It runs for a few seconds before and after a cold start and helps the engine fire smoothly and smoke less. If it fails, the engine starts harder in the cold, smokes white for longer and runs roughly at first, but runs normally once warm.
What causes P0540?
- A burnt-out heating grid
- A failed heater relay, which carries a heavy current
- A corroded or loose heavy cable terminal at the heater
- A damaged control wire between the relay and the engine computer
What to check first for P0540
- Check whether the wait-to-start light behaves as usual when the ignition is switched on in the cold
- Listen for the heater relay clicking on and off
- Inspect the heavy cable terminals at the heater and the relay for corrosion and looseness
- Have the current drawn by the heater measured
Can you drive with P0540?
You can drive safely once the engine is running. Cold starts get harder and smokier, so have it repaired before the cold season.
Clear a code only after the fault is fixed. A code that comes back means the cause is still there, and a warning light left on can hide a second fault behind the first.
Codes on this page
- P0540Intake Air Heater "A" Circuit
- P0541Intake Air Heater "A" Circuit Low
- P0542Intake Air Heater "A" Circuit High
- P0543Intake Air Heater "A" Circuit Open
- P0640Intake Air Heater Control Circuit
Related codes
Checked on · Rafael Soares
These are the generic meanings every manufacturer shares. Each brand adds its own detail, so your car's handbook, its service information and a qualified mechanic have the last word. OdoKeep has no connection with any manufacturer, and the app does not read codes from the car.
