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.
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.
- 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:
| 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:
Use the Manual With the Right Hardware
Pair factory procedures with proven DIY tools so the instructions are easier to execute.
Disclosure: Verified tool recommendations may earn an affiliate commission at no cost to you.
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.
Rather have a pro handle this?
A certified mobile mechanic comes to your home or office. They bring the tools, you stay comfortable. No tow truck, no waiting room, no surprises.
No obligation. See pricing before you book.