1994 Audi S4FACTORY OEM SERVICE PROCEDURE

Fuel Injectors Actuation

  1. Unfasten passenger side A-pillar lower trim. Fold back carpet in right front footwell. Remove cover from electronics box. Remove Injector valve circuit breaker S72 position 2 (Brown holder). See Figure.
  2. Check ECM circuit breaker S64 in position 3 (Red holder). See Figure.
  3. Remove harness connector from fuel injector to be tested. Connect LED tester (US 1115) between connector terminal No. 2 and engine ground. See Figure.
  4. Switch ignition to ON position. LED tester must light up. If LED tester does light up, locate and repair open circuit between terminal No. 37 of Motronic Engine Control Module (ECM) harness connector and terminal No. 2 of fuel injector harness connector being tested. See Figure and Figure . See WIRING DIAGRAMS .
  5. If LED tester still does NOT light up, replace ECM. After replacement of ECM, see ECM IDENTIFICATION and ECM CODING under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS article.
  6. Reinstall injector valve circuit breaker S72. Connect LED tester to terminal 2 of fuel injector harness connector and engine ground.
  7. Switch ignition ON and crank starter for a few seconds. LED tester must light up when ignition is switched ON, and during cranking.
  8. If light goes OUT during starter cranking. Verify that injector valve circuit breaker S72 is Okay.
  9. Using a DVOM, switch to resistance range (mode).
  10. Check continuity (according to wiring diagram), between terminal No. 2 of fuel injector harness connector, see Figure and injector valve circuit breaker S72. See WIRING DIAGRAMS .
  11. Check continuity (according to wiring diagram), between injector valve circuit breaker S72, and terminal No. 31 of fuel pump relay -J17- (relay location 6). See Figure. Also, see WIRING DIAGRAMS .
  12. Check fuel pump relay. See FUEL PUMP RELAY . If necessary, also check control signal to fuel pump relay. See FUEL PUMP RELAY CONTROL SIGNAL .
  13. Connect LED tester between terminal No. 1 and 2 of fuel injector harness being tested. See Figure.
  14. Initiate Output Diagnostic Test Mode (DTM). See OUTPUT DIAGNOSTIC TEST MODE (DTM) in SELF-DIAGNOSTICS article. When fuel injector to be checked is activated during Output DTM, LED tester must blink (maximum 5, times). If LED tester does NOT blink, or if it lights up continuously: Connect (VAG 1598) test box (using VAG 1598/5 adapter cable) only to harness connector of ECM. See CONNECTING VAG 1598 TEST BOX .
  15. Check the flowing wires for continuity or connection to ground using DVOM and wiring diagrams. See IDENTIFYING FUEL INJECTOR HARNESS CONNECTOR & VAG 1598 SOCKET NUMBER  table. See WIRING DIAGRAMS .
  16. If a problem is found (open circuits or shorts to ground). Repair open circuit between ECM harness connector terminal and terminal No. 1 of fuel injector harness connector, or repair, short circuit to ground.
  17. If NO open circuits or shorts to ground are found. Replace ECM. After replacement of ECM, see ECM IDENTIFICATION and ECM CODING under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS article.
IDENTIFYING FUEL INJECTOR HARNESS CONNECTOR (TERMINAL NO. 1) & (VAG 1598) SOCKET NUMBER

Fuel Injector/Cylinder No. VAG 1598 Adaptor Socket No.
1 36
2 17
3 34
4 35
5 16
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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.