P1902

P1902
No bus communication with TWICE.

Fault symptoms
No bus communication with the TWICE.

Condition
The following conditions are applicable:
Trionic:
- Engine has started
- No communication for 10 seconds
TCM:
- The automatic transmission's input shaft speed exceeded 200 rpm once during the present drive cycle.
- No communication for 6 seconds.

Diagnostic help
Some of the following symptoms can perhaps be observed:
- Additional diagnostic trouble codes in the Trionic (P1901, P1923 or P1908).
- Additional diagnostic trouble code in the TCM (P1921)
- Engine fails to start.
- Cruise Control does not work.
- Radio does not work.
- Central locking system does not work.
- Remote control does not work.





Checking the wiring harness
Jiggle the wiring harness at several points and in different directions to detect intermittent breaks and short-circuits in the leads. Observe the multimeter, test lamp or diagnostic tool during the test.





Diagnostic procedure

1 Checking communication
- Turn the ignition switch to ON.





- Select: All systems/Bus configuration in the diagnostic tool's main menu.
- The diagnostic tool shows MISSING when there is no communication for one or more systems.

Is "MISSING" shown for one or more systems?
YES
- See fault diagnosis by symptoms: No contact with one or more bus Systems. No Contact With Any Bus System
NO
- Go to point 2.





2 Checking additional diagnostic trouble codes in the Trionic
- Check whether diagnostic trouble code P1908 has been generated in the Trionic.

Has diagnostic trouble code P1908 been generated in the Trionic?
YES
- Go to point 3.
NO
- Go to point 11.

3 Checking customer complaints

Any complaints that the main instrument unit's speedometer has stopped working?
YES
- Go to point 4.
NO
- Go to point 7.





4 Checking the MIU control module's current supply (+30 circuit)
- Unplug the connector: Main instrument unit 12- pin connector: (540)





- Check the pins in the control module connector and in-line connectors for pin slide-out and poor contact.
- Connect test lamp 86 11 857 to pin 7 of MIU K12's female connector and a good grounding point.





- The test lamp should light.

Function OK?
YES
- Go to point 5.
NO
- Repair or replace the relevant lead.
- Go to point 18.





5 Checking the MIU control module's grounding
- Connect test lamp 86 11 857 to pins 7 and 2 in MIU K12's female connector.





- The test lamp should light.

Function OK?
YES
- Go to point 6.
NO
- Repair or replace the relevant lead.
- Go to point 18.





6 Checking the MIU control module's current supply (+15 circuit)
- Connect test lamp 86 11 857 to pins 1 and 2 in MIU K12's female connector.





- The test lamp should light.

Function OK?
YES
- Go to point 18.
NO
- Repair or replace the relevant lead.
- Go to point 18.





7 Checking the bus lead connections to the Trionic control module (Bus+)
- Unplug the connector: Trionic control module: (430)





- Unplug the connector: TCM control module: (502)





- Unplug the connector: Main instrument unit 12-pin connector: (540)





- Check the pins in the control module connector and in-line connectors for pin slide-out and poor contact.
- Plug in the connector. Main instrument unit 12-pin connector: (540)





- Turn the ignition switch to ON.





- Take a voltage reading.
- Red test lead: Trionic control module: 66





- Black test lead: Good grounding point.
- A reading of 1.5-3.5 V should be obtained

Function OK?
YES
- Go to point 8.
NO
- Repair or replace the relevant lead.
- Go to point 18.





8 Checking the bus lead connections to the Trionic control module (Bus-)
- Take a voltage reading.
- Red test lead: Trionic control module: 19





- Black test lead: Good grounding point.
- A reading of 1.5-3.5 V should be obtained

Function OK?
YES
- Go to point 9.
NO
- Repair or replace the relevant lead.
- Go to point 18.





9 Checking the bus lead connections to the TCM control module (Bus+)
- Take a voltage reading.
- Red test lead: Control module TCM: 1.





- Black test lead: Good grounding point.
- A reading of 1.5-3.5 V should be obtained

Function OK?
YES
- Go to point 10.
NO
- Repair or replace the relevant lead.
- Go to point 18.





10 Checking the bus lead connections to the TCM control module (Bus-)
- Take a voltage reading.
- Red test lead: Control module TCM: 22.





- Black test lead: Good grounding point.
- A reading of 1.5-3.5 V should be obtained

Function OK?
YES
- Go to point 18.
NO
- Repair or replace the relevant lead.
- Go to point 18.





11 Checking the TWICE control module's current supply (+30 circuit)
- Unplug the connector: Control module TWICE: (632)





- Check the pins in the control module connector and in-line connectors for pin slide-out and poor contact.
- Connect test lamp 86 11 857 to pin 43 of the control module's female connector and a good ground.





- The test lamp should light.

Function OK?
YES
- Go to point 12.
NO
- Repair or replace the relevant lead.
- Go to point 18.





12 Checking the TWICE control module's grounding
- Connect test lamp 86 11 857 to pins 43 and 37 of the control module's female connector.





- The test lamp should light.

Function OK?
YES
- Go to point 13.
NO
- Repair or replace the relevant lead.
- Go to point 18.





13 Checking the TWICE control module's current supply (+15 circuit)
- Connect test lamp 86 11 857 to pins 16 and 37 of the control module's female connector.





- The test lamp should light.

Function OK?
YES
- Go to point 14.
NO
- Repair or replace the relevant lead.
- Go to point 18.





14 Checking the bus leads between the TWICE and MIU (Bus+)
- Unplug the connector: Main instrument unit 12-pin connector: (540)





- Take a resistance reading
- Red test lead: Control module TWICE: 38





- Black test lead: Main instrument unit 12-pin connector: 5
- A reading of 0-1 ohm should be obtained

Function OK?
YES
- Go to point 15.
NO
- Repair or replace the relevant lead.
- Go to point 18.





15 Checking the bus leads between the TWICE and MIU (Bus-)
- Take a resistance reading
- Red test lead: Control module TWICE: 15





- Black test lead: Main instrument unit 12-pin connector: 12
- A reading of 0-1 ohm should be obtained

Function OK?
YES
- Go to point 16.
NO
- Repair or replace the relevant lead.
- Go to point 18.





16 Checking whether the bus leads are shorted to ground (Bus+)
- Turn the ignition switch to ON.





- Take a voltage reading.
- Red test lead: Control module TWICE: 38





- Black test lead: Good grounding point.
- A reading of 1.5-3.5 V should be obtained

Function OK?
YES
- Go to point 17.
NO
- Repair or replace the relevant lead.
- Go to point 18.





17 Checking whether the bus leads are shorted to ground (Bus-)
- Take a voltage reading.
- Red test lead: Control module TWICE: 15





- Black test lead: Good grounding point.
- A reading of 1.5-3.5 V should be obtained

Function OK?
YES
- Go to point 18.
NO
- Repair or replace the relevant lead.
- Go to point 18.





18 Final check
- Clear the diagnostic trouble codes in all systems.





- Carry out a drive cycle:
- Drive the car at varying engine loads and rpm for five minutes.
- Evaluate the drive cycle:
- Check whether the diagnostic trouble code has recurred.

Function OK?
YES
- The steps taken to rectify the fault were correct.
NO
- See "Before changing a control module." Before Changing A Control Module