Test sequence

Pull connector off coolant temperature sender.
NOTE: Disconnecting the ECT sensor connector simulates a "cold" engine condition and turning on the ignition starts the glow plug process.

Fig 1: Pulling Connector Off Coolant Temperature Sender

Courtesy of VOLKSWAGEN OF AMERICA, INC.

Disconnect glow plug connector from glow plug.
Switch on ignition.
Connect multimeter VAG 1526 to measure voltage between No. 1 cylinder glow plug connector and vehicle ground. Then between cylinder No. 3 glow plug connector and vehicle ground. Specification:
Specification:
Battery voltage for approx. 20 seconds
If no voltage is present, check circuit
Check DTC memory, if necessary, repair any malfunctions and erase DTC memory; see DIAGNOSTIC TROUBLE CODE (DTC) MEMORY, CHECKING AND ERASING .
Display readiness code, see READINESS CODE, DISPLAYING . If DTC memory has been erased or Engine Control Module (ECM) was disconnected, reset readiness code; see READINESS CODE, SETTING .