A4 & S4

Check engine timing fuses in fuse box, replace as necessary. Ensure battery voltage is 11.7 volts or more. Charging system tests okay. Disconnect Engine Control Module (ECM) harness connector. In A4 and S4 models, ECM is located in left rear corner of engine compartment, in electronics box. Connect VAG 1598/31 test box to ECM harness connector (leave ECM disconnected). Turn ignition on. Using DVOM, measure voltage between specified VAG test box sockets. See CHECKING ENGINE CONTROL MODULE VOLTAGE SUPPLY table. If voltage is not as specified, go to next step. If voltage is as specified, go to step 3 .

CHECKING ENGINE CONTROL MODULE VOLTAGE SUPPLY

Between VAG Test Box Sockets	Specification
2 & 3	Battery Voltage
1 & 3	Battery Voltage
2 & 62	Battery Voltage

Check for open, short to ground or short to voltage in suspect circuit between ECM and ECM voltage supply relay. See WIRING DIAGRAMS article. To test ECM power supply relay, go to ENGINE CONTROL MODULE POWER SUPPLY RELAY . If problem is found, repair as necessary. After repair go to next step.
Using scan tool, clear DTCs and generate a ECM readiness code. See FUNCTION 05 - CLEARING DIAGNOSTIC TROUBLE CODES and READINESS CODE under SELF-DIAGNOSTIC SYSTEM in appropriate SELF-DIAGNOSTICS article. Test drive vehicle. Using scan tool, retrieve DTCs. If DTC does not reset, testing is complete.