Power Supply Relay, Checking
Power Supply Relay, Checking
Observe all safety precautions: => [ Safety Precautions ] Generic Scan Tool
View clean working conditions: => [ Clean Working Conditions ] Clean Working Conditions
Use only gold-plated terminals when servicing any component with gold-plated electrical harness connector terminals.
For wiring diagrams, component locations, and connector views, Refer to the applicable wiring diagram.
Special tools, testers and auxiliary items required
• multimeter.
• Wiring diagram.
Test requirements
• The Motronic Engine Control Module (ECM) (J623) fuses OK.
• Battery voltage at least 12.5 volts.
• All electrical consumers such as, lights and rear window defroster, switched off.
• Vehicles with automatic transmission, selector lever in position "P" or "N".
• A/C switched off.
• Ground (GND) connections between engine/transmission/chassis OK.
• Ignition switched off.
Test procedure
- Perform a preliminary check to verify the customers complaint. Refer to => [ Preliminary Check ] Preliminary Check
Start diagnosis
- Remove the Power Supply Relay (terminal 50) (J682). Refer to appropriate service information.
Checking voltage
- Using a multimeter, check the Power Supply Relay (terminal 50) (J682) socket 2/30 to Ground (GND).
Specified value: battery voltage.
If the specified value was not obtained:
- Check the wiring connections from the Battery to the Power Supply Relay (terminal 50) (J682) socket 2/30 for an open circuit or a short circuit.
- Check the wiring connections for damage, corrosion, loose or broken terminals.
- If necessary, repair the faulty wiring connection.
If the specified value was obtained:
- Switch the ignition on.
- Using a multimeter, check the Power Supply Relay (terminal 50) (J682) socket 8/87 to Ground (GND).
Specified value: battery voltage.
If the specified value was obtained:
- Switch the ignition on.
- Using a multimeter, check the Power Supply Relay (terminal 50) (J682) socket 6/85 to Ground (GND).
Specified value: battery voltage.
Checking wiring
If the manufacturers test box is being used, perform the following step.
- Install the test box.
If the manufacturers test box is not being used, perform the following step.
- Remove the Motronic Engine Control Module (ECM) (J623). Refer to appropriate service information.
- Using a multimeter, check the Power Supply Relay (terminal 50) (J682) socket 3/86 to the Motronic Engine Control Module (ECM) (J623) electrical harness connector T94 terminal 92 for resistance.
Specified value: 2.0 ohms Max.
If the specification was not obtained:
- Check the wiring for a short circuit to Battery (+), or an open circuit.
- Check the electrical harness connector for damage, corrosion, loose or broken terminals.
- If necessary, repair the faulty wiring connection.
If no malfunction is found in the wiring:
Checking activation
- Switch the ignition on.
- Using a multimeter, check the Power Supply Relay (terminal 50) (J682) socket 4/85 to the Motronic Engine Control Module (ECM) (J623) electrical harness connector T94 terminal 69 for voltage.
- Switch the ignition off.
Specified value: 0.5 V Max.
If the specified value was obtained:
- Replace the Power Supply Relay (terminal 50) (J682). Refer to appropriate service information.
If the specified value was not obtained:
- Check the wiring for a short circuit to Battery (+), or an open circuit.
- Check the wiring connection for damage, corrosion, loose or broken terminals.
- If necessary, repair the faulty wiring connection.
If no malfunction is found in the wiring and voltage supply was not OK:
- Replace the Motronic Engine Control Module (ECM) (J623). Refer to appropriate service information.
Final procedures
After the repair work, the following work steps must be performed in the following sequence:
1. Check the DTC memory. Refer to => [ Diagnostic Mode 03 - Read DTC Memory ] Diagnostic Modes 01 - 0A.
2. If necessary, erase the DTC memory. Refer to => [ Diagnostic Mode 04 - Erase DTC Memory ] Diagnostic Modes 01 - 0A.
3. If the DTC memory was erased, generate readiness code. Refer to => [ Readiness Code ] Readiness Code.