P1781

P1781
Ignition angle intervention - discontinuity/short circuit to ground -

P1782
Ignition angle intervention - short circuit to plus -

Function
With this control, the transmission control unit is connected with the ECM control unit. At the shifting time, the engine control unit reacts by retarding the ignition angle. This reduces the engine torque during the shifting process. This also has a positive effect on the shifting comfort and increases the service life of shifting elements. Hard shifting takes place if this signal is faulty.

Diagnosis conditions
DTC P1781 is detected and stored with the engine at idle speed and DTC P1782 during shifting.





Wiring diagram





Diagnosis procedure P1781

NOTE: The ignition-angle intervention function can be tested with system tester 9288 (drive Links/Ignition.angle intervention).





Check voltage drop at connector X4/1 pin 7.
1. Remove cover on connector X4/1.
2. Connect system tester and call up menu item Drive Links/Ignition-angle intervention.
3. Measure voltage at pin 7. Set-point: > 4.5 Volt
4. Let engine run at approx. 3000 rpm and trigger signal with tester. The engine speed and voltage must drop briefly. Connector X4/1 (below left-hand seat)

Check wire from transmission control unit to ECM control unit for continuity.
1. Pull off transmission control unit connector and ECM control unit connector.
2. Connect ohmmeter to transmission control unit connector pin 20 and ECM control unit connector pin 42.
- Indication: 0...5 ohms
- If infinite resistance ohm is indicated, check wiring harness for crushing and chafing damage.

Check wire from transmission control unit to ECM control unit for short circuit to ground.
1. Connect ohmmeter to transmission control unit connector pin 20 and ground.
- Indication: infinite resistance
- If 0...5 ohms is indicated, check wiring harness for crushing and chafing damage.





Diagnosis procedure DTC 1782





Check voltage drop at connector X4/1 pin 7.
1. Remove cover on connector X4/1.
2. Connect system tester and call up menu item Drive links/ignition-angle intervention.
3. Measure voltage at pin 7. Set-point: > 4.5 Volt
4. Let engine run at approx. 3000 rpm and trigger Signal with tester. The speed and voltage must drop briefly. Connector X4/1 (below the left-hand seat)

Check wire from transmission control unit to ECM tester for short circuit to plus.
1. Pull off transmission control unit connector and ECM control unit connector.
2. Switch on ignition.
3. Connect voltmeter to transmission control unit connector pin 20 and ground.
- Indication: 0 Volt
- If battery voltage is indicated, check wiring harness for crushing and chafing damage.