Powertrain, generic · Vehicle speed, idle control and auxiliary inputs

P0542 Intake Air Heater A Circuit High

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

Some diesels – typically Cummins engines in Ram pick-ups and commercial vehicles, and Iveco – heat the intake air with a grid heater in the intake manifold instead of or alongside glow plugs. It draws very high current through a relay (on recent Ram a solid-state relay) and is switched by the engine module before and after starting; CARB requires cold-start aids to be monitored. P0542 means the voltage stays high although the heater is commanded on – a control line shorted to positive or a relay that does not switch. A shorted or welded relay can also power the heater permanently; Ram recalled 6.7 L Cummins trucks because a shorted heater relay could start a fire. No manufacturer document available to us uses this code; GM's Duramax LML has an intake heater but reports it under its own codes P154A–P154D.

Likely causes

Heater relay faulty (solid-state relay shorted, contacts stuck)
Control line shorted to positive, harness chafed on a power cable
Power circuit overheated, cable scorched
Engine module driver

Symptoms

  • Check engine light on
  • Battery drained when heater stays on
  • Burning smell or scorched wiring at the relay

Repair estimate

DifficultyMediumDIY possible
Parts and labour€50–500
Time0.5–3 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

intake air heaterheater relayheater wiringengine control module

Related codes

P0540P0541P0543P2608P2609

References: patents.google.com, patents.google.com, static.nhtsa.gov, static.nhtsa.gov.