Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
2002 Audi A4 Base, 1.8 C, StandardFACTORY OEM SERVICE PROCEDURE
Test sequence
- Connect test box V.A.G 1598/31 to wiring harness for ECM; do not connect directly to ECM. See ELECTRICAL TESTING USING VAG1598/31 TEST BOX .
- Switch ignition on.
NOTE:
- The positive voltage supply to the ECM is provided via terminal 3 (terminal 15) and terminal 62 (terminal 30).
- The ground (GND) connection to the ECM is provided via terminal 1 and terminal 2.
- Connect multimeter as follows to measure voltage:
ECM POWER/GROUND CIRCUIT CHECK: SOCKET 1, 2, 62 MEASURE
| Test box V.A.G 1598/31 Socket | Measure to |
|---|---|
| 1 | Battery positive (B+) |
| 2 | Battery positive (B+) |
| 62 | Engine ground (GND) |
- Specified value: approx. battery voltage (B+)
- Connect multimeter as follows to measure voltage:ECM POWER/GROUND CIRCUIT CHECK: SOCKET 3 MEASURE
Test box V.A.G 1598/31 Socket Measure to 3 Engine ground (GND) - Switch ignition on.
- Specified value: approx. battery voltage (B+)
- Check wiring connections.
See appropriate System Wiring Diagram article.
- Connect multimeter as follows to measure voltage:ECM POWER/GROUND CIRCUIT CHECK: SOCKET 121 MEASURE
Test box V.A.G 1598/31 Socket Measure to 121 (1) Engine ground (1) The Motronic Engine Control Module (ECM) Power Supply Relay -J271- carries voltage on terminal 121 of ECM after switching off the ignition for up to 15 minutes. - Switch ignition on.
- Specified value: approx. battery voltage (B+)
- Check wiring connections.
See appropriate System Wiring Diagram article.
- Check Motronic Engine Control Module (ECM) Power Supply Relay -J271-. See MOTRONIC ECM POWER SUPPLY RELAY - J271-, CHECKING .
If the specified values are not obtained:
If specified value is not obtained:
Factory Service Tools
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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.