The intake air heater circuit has failed. On diesels this makes cold starting rough and smoky in winter while being invisible in summer.
P0540 — also written PO54O, P 0540, 0540 — is the OBD-II code for intake air heater circuit (glow / grid heater). Same code, same fix: this page covers every spelling of it.
P0540 is a electrical fault code, typically costing £90–£400 to put right in a UK garage.
What causes P0540?
- Failed intake heater element
- Failed heater relay
- Corroded high-current feed
- Broken earth strap
How P0540 is fixed
- Test the relay and the current draw at the heater
- Replace the relay or element
- Clean and remake the earth
P0540 repair cost in the UK
Most P0540 repairs land between £90–£400 including parts and labour. The spread is wide because the cheap fix (a sensor, a hose, a leak) and the expensive fix (a major component) throw the same code — which is why a proper diagnosis before parts are bought saves the most money.
Can you drive with P0540?
Yes, though expect harder cold starts.
Urgency: low.