Failed intake air heater element (open circuit within the heater); Blown fuse or fusible link in the heater power supply; Faulty heater relay or contactor that does not close; Damaged, corroded or loose wiring and connectors between the control unit, relay and heater; Poor earth connection or high resistance in the heater power feed cable; Fault in the control unit driver circuit for the heater or relay.

P0543

Intake Air Heater A Circuit Open.

Generic
Powertrain
Generic code
Low severity

How this code is built

P: SystemPowertrain
0: Defined bySAE, the same on every car
5: AreaVehicle speed, idle control and auxiliary inputs
43: FaultThe specific fault in that area

What it means

P0543 means the engine control unit has detected an open circuit in the intake air heater 'A' circuit, as defined by SAE J2012. The heater, usually found on diesel engines to aid cold starting and warm-up, is not completing its electrical circuit. The control unit sets the code when it commands the heater or its relay and sees no expected current flow or feedback, or sees a voltage that indicates a break in the circuit.

Symptoms

Malfunction indicator lamp on, and possibly a glow plug or engine warning light
Hard starting or extended cranking in cold weather
White or grey smoke and rough running on a cold start
Rough idle or misfire until the engine warms up
Slightly higher fuel consumption or slow warm-up in cold conditions
No symptoms at all in warm weather

Possible causes

Failed intake air heater element (open circuit within the heater)likely
Blown fuse or fusible link in the heater power supplylikely
Faulty heater relay or contactor that does not closelikely
Damaged, corroded or loose wiring and connectors between the control unit, relay and heaterpossible
Poor earth connection or high resistance in the heater power feed cablepossible
Fault in the control unit driver circuit for the heater or relayrare

How to diagnose

Read all stored codes and freeze frame data, noting the coolant and ambient temperature when the code set, then check for related glow plug or battery voltage codes
Check the battery condition and charging voltage, as low voltage can upset heater circuit monitoring
Inspect the heater fuse and any fusible link, and find out why it failed if it has blown
Visually inspect the heater wiring, connector and relay for heat damage, corrosion, chafing or loose terminals
Using the manufacturer's wiring diagram, command the heater on with a suitable diagnostic tool and check for battery voltage at the relay and at the heater feed
Test the relay or contactor operation and its coil supply and control signal
Check the heater element for continuity and resistance against the manufacturer's specification, and check the earth path
If supply, earth and heater all prove good, check the control unit output and wiring for open circuit; procedure varies by model and engine

How to fix

Replace the open-circuit intake air heater element
Replace the blown fuse or fusible link after finding and correcting the cause of the overload
Replace the faulty heater relay or contactor
Repair or replace damaged wiring and clean or renew corroded connectors and terminals
Restore a good earth or power feed connection, including cleaning and tightening cable ends
Repair or replace the control unit only after all wiring and components are proven good

Can I keep driving?

Low severity

The car can normally be driven, as the fault mainly affects cold starting and warm-up. Book it in soon, especially before cold weather, as starting may become difficult and emissions may be higher on cold starts.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.