P0543
Intake Air Heater A Circuit Open
The intake air heater (grid heater) on path A - used on cold-start of diesel engines to warm intake air for reliable combustion - has an open control circuit. Without it, cold-start emissions and idle quality on cold days suffer.
- Check engine light: Yes
- Emissions related: Yes
- Repair difficulty: medium
Common causes
Ordered by how often each turns out to be the cause.
- Open in harness, relay or heater elementCommon
- Pin pushed back out of connector bodyLess likely
- Cracked solder joint inside the module or sensorLess likely
Parts involved
- Intake Air Heater A
- Heater A Relay
P0543 is a generic OBD-II code defined by SAE J2012. Exact wording and diagnostic procedure vary by manufacturer and model. Code definitions are drawn from the public-domain OBDex dataset; the workshop notes are our own.