Possible causes
– Intake air heater relay
Tech description
The most common problem that sets code p0540 is the air intake relay
Symptoms
– Engine Light ON (or Service Engine Soon Warning Light)
P0540 GMC OBD Code Description
The Engine Control Module (ECM) uses an Intake Air Heater (IAH) to warm the incoming air for proper cylinder combustion. The ECM grounds the control coil of the IAH relay to energize the heater during cold operation.