P0543: Intake Air Heater A Circuit Open

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. P0543 means an open circuit at heater A – in the control line or relay coil, or depending on the maker in the power circuit or heating element itself. It is detected by driver diagnosis with the output off, by a missing voltage dip on switching on or by a missing temperature rise. 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.

Low severity. Can I keep driving?Yes, you can normally keep driving and take it to a repair shop when convenient.

Symptoms

Check engine light on
Starting problems in the cold
White smoke or knocking while warming up

Most likely causes

Heating grid burnt out
Relay coil or contact open
Broken cable, loose nut or ring terminal at the grid
Fusible link in the heater circuit

What to check, in order

Start with the simplest. You can tick off each step.

With the engine cold, compare the reading with the outside temperature
Check the continuity of the wire between the component and the control module.
Check the connector
Measure the sensor's resistance against the manufacturer's specification
Check power and ground before replacing it

Good to know

Repair difficulty: medium
It affects emissions.

What each character of P0543 means

P: Powertrain: engine and transmission
0: Generic code: same on every make
5: Speed and idle
43: Specific fault in that system

Frequently asked questions

Can I keep driving with code P0543?

Yes, you can normally keep driving and take it to a repair shop when convenient.

What causes code P0543?

The most common causes are: heating grid burnt out; relay coil or contact open; broken cable, loose nut or ring terminal at the grid.

Related codes

Sources

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.