Auxiliary Heater Check: Troubleshooting & Repair

Hello!
How do I check if power is reaching the glow plug controller (Audi A3 1.9 TDI 66KW) and if the glow plugs are working? Is this possible with a cold engine at idle? Can the connectors be disconnected with the engine running, or will this trigger an error code in the engine control unit?
Could a fault in the auxiliary heater be identified by reading the error memory, or is it not related?

Thank you for your help!

Best regards, Daniel.

Hi Daniel,

AFAIK, the error memory only stores information about interruptions or short circuits in the relay windings, but not about any faults in the load circuit.

Using VAGCOM, you can easily check this component with the engine off using the actuator diagnostics function. In a quiet environment, you can hear the bubbling of water at the glow plugs approximately every 2 seconds. Also, with high heating power, the interior lighting should become slightly dimmer than with low power – in 95% of cases, this indicates that everything is okay.