Communication Problems With Scan Tool

COMMUNICATION PROBLEM WITH THE SCAN TOOL





Fault Sources

^ If the engine starts:
- Poor battery voltage.
- Break or short circuiting to ground in the lead to the Data Link Connector (DLC).
- Faulty wiring in the Scan Tool (ST).

^ If the engine does not start:
- 15-supply short circuited to ground between fuse and control module.
- Break in 15-supply.
- Break in 30-supply.
- Break in supply from main relay.
- Break in control signal, main relay.

NOTE: If the communication problem only occurs when the engine is started: Connect a battery charger or extra battery.

TESTING PROCEDURE





Starting the Engine
^ Does the engine START?

Yes:
- Select the communication lead.
No:
- Proceed to: Checking the Fuse section below.





Selecting the Communication Lead
^ Does the fault occur only when an attempt is made to read DTCs in the AW 50-42 TCM?

Yes:
- Proceed to: Checking the AW 50-42 DLC Lead section below.
No:
- Check the Motronic 4.3 DLC lead.





Checking the Motronic 4.3 DLC Lead
^ Ignition ON.
^ Connect a voltmeter between DLC 2 and ground.

The voltmeter should show more than 5 Volts.

If the reading is OK:
- Check the DLC wiring to the ST for signs of damage.
If the reading is incorrect:
- Check resistance to ground in the ECM's DLC.





Checking Resistance to Ground in the ECM's DLC
^ Ignition OFF.
^ Wait for approx. 150 seconds.
^ Connect an ohmmeter between DLC connector 2 and ground.

If the ohmmeter shows infinite resistance:
- Check the lead between ECM B5 and DLC connector 2 for signs of a break.
If the ohmmeter shows approx. 0 Ohms:
- Check the lead between ECM B5 and DLC connector 2 for signs of short circuiting to ground.
- On cars with an OBD II DLC: Check also the lead between OBD 11 DLC 3 and ECM B5 for signs of short circuiting to ground.





Checking AW 50-42 DLC Lead
^ Ignition ON.
^ Connect a voltmeter between DLC connector 1 and ground.

The voltmeter should show more than 5 Volts.

If the reading is OK:
- Check the DLC wiring to the ST for signs of damage.
If the reading is incorrect:
- Check the resistance to ground in the TCM's DLC lead.





Checking Resistance to Ground in the TCM's DLC Lead
^ Ignition OFF.
^ Wait for approx. 150 seconds.
^ Connect an ohmmeter between DLC connector 1 and ground.

If the ohmmeter shows infinite resistance:
- Check the lead between TCM B5 and DLC connector 1 for signs of a break.
If the ohmmeter shows approx. 0 Ohms:
- Check the lead between TCM B5 and DLC connector 1 for signs of short circuiting to ground.





Checking the Fuse
^ Check that fuse 1 is intact.

If the fuse is intact:
- Check the 15-supply in front of the fuse.
If the fuse is not intact:
- Check the circuit for signs of short circuiting to ground.





Checking the 15-Supply in Front of the Fuse
^ Ignition ON.
^ Connect a voltmeter between the Right Hand socket in the fuse holder for fuse 1 and ground.

The voltmeter should show battery voltage.

If the reading is OK:
- Proceed to: Checking the 15-Supply After the Fuse section below.
If the reading is incorrect:
- Check the 15-supply from the ignition switch.





Checking the 15-Supply From the Ignition Switch
^ Ignition OFF.
^ Undo the connector from the ignition switch.
^ TURN the ignition key to position II.
^ First connect an ohmmeter between connector 15 and 30 on the ignition lock and then between connector 15 and the other connector 30 on the ignition lock.

The ohmmeter should show approx. 0 Ohms in both cases.

If the readings are OK:
- Check the voltage supply to the ignition switch.
If a reading is incorrect:
- Test with a new ignition switch.





Checking the Voltage Supply to the Ignition Switch
^ Ignition OFF.
^ Undo the ignition switch's connector.
^ First connect a voltmeter between connector 30 on the ignition lock's coupling and ground, and then between the other connector 30 on the ignition lock's coupling and ground.

The voltmeter should show battery voltage in both cases.

If the readings are OK:
- Check the lead between ignition switch connector 15 and fuse 1 for signs of a break.
If the readings are incorrect:
- Check the lead between the battery ground terminal and ignition switch connector 30 for signs of a break.





Checking the 15-Supply After the Fuse
^ Connect the break-out box and check the ground connectors.
^ Reinstall the fuse.
^ Connect the ECM.
^ Ignition ON.
^ Connect a voltmeter between #42 (ECM A42) and #12 (ECM A12).

The voltmeter should show battery voltage.

If the reading is OK:
- Check the 30-supply.
If the reading is incorrect:
- Check the lead between the fuse holder's left socket and ECM A12 for signs of a break.





Checking the 30-Supply
^ Ignition ON.
^ Connect a voltmeter between #42 (ECM A42) and #26 (ECM A26).

The voltmeter should show battery voltage.

If the reading is OK:
- Check voltage supply from the main relay.
If the reading is incorrect:
- Check the lead between ECM A26 and the battery for signs of a break.





Checking Voltage Supply From the Main Relay
^ Ignition ON.
^ Connect a voltmeter between #27 (ECM A27) and #42 (ECM A42) on the break-out box.

The voltmeter should show battery voltage.

If the reading is OK:
- Check all signals to and from the Motronic 4.3 ECM.
- See: System Diagnosis / Diagnostic Charts / Non-Trouble Code Charts / ECM Pinout/Terminal I.D. Charts.
If the reading is incorrect:
- Check the voltage supply to main relay connector 4.





Checking Voltage Supply to Main Relay Connector 4
^ Ignition OFF.
^ Disconnect the connector from the main relay (2/32).
^ Connect a voltmeter between main relay connector 4 and ground.

The voltmeter should show battery voltage.

If the reading is OK:
- Check the voltage supply to main relay connector 2.
If the reading is incorrect:
- Check the lead between main relay connector 4 and the battery positive terminal for signs of a break.





Checking Voltage Supply to Main Relay Connector 2
^ Ignition OFF.
^ Undo the main relay.
^ Connect a voltmeter between main relay connector 2 and ground.

The voltmeter should show battery voltage.

If the reading is OK:
- Check the control signal to main relay.
If the reading is incorrect:
- Check the lead between main relay connector 2 and battery positive terminal for signs of a break.





Checking the Control Signal to the Main Relay
^ Ignition ON.
^ Disconnect the main relay.
^ Connect a voltmeter between main relay connector 1 and the battery positive terminal.

The voltmeter should show battery voltage.

If the reading is OK:
- Check the voltage supply from the main relay.
If the reading is incorrect:
- Check the lead between ECM A41 and main relay connector 1 for signs of a break.





Checking Voltage Supply From the Main Relay
^ Ignition ON.
^ Connect the main relay to the connector.
^ The relay should click when it is coupled to the connector.

If the relay clicks:
- Check the lead between ECM A27 and main relay connector 3 for signs of a break.
If the relay does not click:
- Check the signal lead.





Checking the Signal Lead
^ Ignition OFF.
^ Remove the main relay from the connector.
^ Connect an ohmmeter between main relay connector 3 and ground.

NOTE: This lead also goes to:
All injectors connector 1.
Heated Oxygen Sensor preheating connector 1.
Idle Air Control Valve connector 2.
Mass Air Flow Sensor connector 3.
EGR controller connector 1.
Turbocharger control valve connector 1.
EVAP valve connector 1.

If the ohmmeter shows approx. 0 Ohms:
- Check the lead between ECM A27 and main relay connector 3 for signs of short circuiting to ground.
If the ohmmeter shows more than approx. 0 Ohms:
- Test with a new main relay.


^ When the fault has been rectified, a new main relay should be fitted.