DTC 231

EG. DTC 2-3-1
2-3-1 Irregular TP sensor signal

Principle of operation

Supplied by a sensor mounted at the throttle, via the Motronic 1.8 ECM, the TP sensor signal describes the degree of throttle opening. The signal can vary from 0.2 to 4.8 V, increasing with the opening. The value should be between 4.0 and 4.8 V at WOT and between 0.2 and 1.0 V at CTP. Among other functions, the TCM uses the signal to control the gearshifting points and transmission line pressure.

Fault description

The TCM signal varies considerably. The fault may be in one of the circuit components or wiring (connectors and connections), but may also be due to interference from other on-board systems. The transmission operates at high line pressure and the MIL lights.





Circuit description

The circuit consists of the TCM, connectors, TP sensor and Motronic 1.8 ECM.





1
Display Motronic 1.8 DTCs in test mode 1

Using test mode 1, check whether DTC have been stored in Motronic 1.8 diagnostics. How to display codes for Motronic 1.8 can be found in Computers and Control Systems, Testing and Inspection. Testing and Inspection

- If DTC have been recorded, carry out troubleshooting as described in Computers and Control Systems, Testing and Inspection. Testing and Inspection

- If no DTC has been recorded, proceed to step 2.





2
Measuring TP sensor signal from Motronic 1.8 ECM to AW 30-4O/AW 30-43 TCM

- Switch off ignition.
- Connect break-out box between AW 30-40/AW 30- 43 TCM and wiring.
- Switch on ignition.
- Start and idle engine.

Connect voltmeter across # 31 (VTH) and # 12 (SG) on break-out box.

- Instrument should indicate low voltage (at least 0.2 V) at CTP and high voltage (max. 4.8 V) at WOT.

Proceed to step 3.

3
Check ground terminal connection on transmission

- Check that no leads from ignition system or accessories are connected in parallel with lead from TP sensor.
- Check that no factory-fitted systems are connected to signal ground (SG).
- Idle engine.

Connect voltmeter across # 12 (SG) and ground terminal at A-post.

- Instrument should indicate less than 0.7 volt it ECM is connected securely to ground terminal.

Note reading for comparison with reading from step 5.
Proceed to step 4.





4
Measuring TP sensor signal from Motronic 1.8 ECM

- Switch off ignition.
- Remove fuse 24.
- Connect break-out box to Motronic 1.8 ECM.
- Install fuse 24.
- Switch on ignition.
- Idle engine.

Connect voltmeter across # 49 (VTH) and # 19 (SG) on break-out box.

- Instrument should indicate low voltage (at least 0.2 V) at CTP.

Switch off engine.

- Instrument should indicate high voltage (max. 4.8 V) at WOT.

If instrument indicates other value, carry out troubleshooting for DTC in Computers and Control Systems, Testing and Inspection. Testing and Inspection

5
Check Motronic 1.8 ground terminal connection

- Idle engine.

Connect voltmeter across # 19 (SG) and ground terminal at A-post.

- Instrument should indicate less than 0.7 V if ECM is connected securely to ground terminal.

Conclusions

- If difference between voltage measured in steps 3 and 5 exceeds 0.1 V, ground terminal connections are poor. Check and rectify connections.
Return to Testing and Inspection. Diagnostic Procedures

- If instrument indicates other value, carry out troubleshooting for DTC in Computers and Control Systems, Testing and Inspection. Testing and Inspection