P0543 Intake Air Heater A Circuit Open

P0543 indicates an open Intake Air Heater A circuit. The controller does not see expected continuity or current flow through the intake heater path.

Code details

Generic OBD-II · P0

System: Speed / Idle
Code type: Generic (SAE / ISO controlled)
Standard: SAE J2012 / ISO 15031-6

Diagnostic boundary

A diagnostic trouble code reports that a monitored test failed. It does not prove one specific part is bad, and manufacturer logic can add vehicle-specific conditions.

Do not replace control modules for P0543 until the high-current heater circuit is load-tested.

Symptoms of P0543

Unstable, high, or low idle, or stalling.
Erratic speedometer, cruise-control, or shift behaviour.
Check-engine light with a hesitation or surge.

Common causes of P0543

A dirty throttle body, idle-control valve, or throttle-position sensor.
A failing vehicle-speed or wheel-speed sensor, or its wiring.
Vacuum leaks or a related sensor forcing the idle/speed strategy.

Useful checks before replacing parts

Measure heater element resistance, supply voltage, relay output, fuse link continuity, ground path, current draw, and freeze-frame temperature data.
Inspect unplugged connectors, burned terminals, open heater elements, broken high-current wiring, corroded grounds, and failed relay contacts.
Verify the open at the heater and at the control side before replacing the heater assembly.

Related OBD-II codes

These nearby speed / idle entries can help compare wording and pin down the fault area.