Checking the OBD II Socket

CHECKING THE OBD II DATA LINK CONNECTOR

General
^ OBD II is a diagnostic system required by law. The OBD II Data Link Connector (DLC) can be used to connect a general fault-tracing instrument to help read off DTCs and parameters. OBD II contains the DTCs and parameters relating to emissions.

Conditions
^ DTCs missing.
^ The fault is permanent.

Fault Causes
^ Communication lead short circuited to ground.
^ Break in communication, power ground, signal ground or voltage lead.

TESTING PROCEDURE





Removal of OBD II DLC
^ Remove:
- Coin tray.
- OBD II DLC.
^ Measure with a multimeter at the rear of the OBD II DLC.
^ Then continue with Check the Power Ground Lead section below.





Check the Power Ground Lead
^ Ignition OFF.
^ Wait for 150 seconds.
^ Connect an ohmmeter between the OBD II DLC's connector 4 and ground.

The ohmmeter should show approx. 0 Ohms.

If the reading is OK:
- Check the signal ground lead.
If the reading differs:
- Check the lead between the OBD II DLC's connector 4 and the ground point at the A-post on the passenger's side (31/15) for signs of a break.
- After rectification: Check the signal ground lead.





Checking the Signal Ground Lead
^ Ignition OFF.
^ Connect an ohmmeter between the OBD II DLC's connector 5 and ground.

The ohmmeter should show approx. 0 Ohms.

If the reading is OK:
- Check the voltage lead.
If the reading differs:
- Check the lead between the OBD II DLC's connector 5 and the engine ground point (31/33) for signs of a break.
- After rectification: Check the voltage lead.





Checking the Voltage Lead
^ Ignition OFF.
^ Connect a voltmeter between the OBD II DLC's connector 16 and ground.

The voltmeter should show battery voltage.

If the reading is OK:
- Check the OBD II communication lead (ECM).
If the reading differs:
- Check fuse no. 15.





Checking Fuse No. 15
If the fuse is intact:
- Check the 30-supply ahead of the fuse.
If the fuse has blown:
- Check the electric circuit for signs of short circuiting to ground.
- After rectification; Check the OBD II communication lead (ECM).





Checking the 30-Supply Ahead of the Fuse
^ Ignition OFF.
^ Connect a voltmeter from the rear socket of the fuse-holder to fuse 15 and ground.

The voltmeter should show battery voltage.

If the reading is OK:
- Check the lead between fuse 15 and the OBD II DLC's connector 16 for signs of a break.
- After rectification: Check the OBD II communication lead (ECM).
If the reading differs:
- Check the lead between fuse 15 and the battery's positive terminal for signs of a break.
- After rectification: Check the OBD II communication lead (ECM).





Checking the OBD II Communication Lead (ECM)
^ Ignition OFF.
^ Disconnect the AW Transmission Control Module (TCM).
^ Connect an ohmmeter between the OBD II DLC's connector 7 and ground.

The ohmmeter should show 90 - 110K Ohms.

If the reading is OK:
- Check the OBD II communication lead (TCM).
If the ohmmeter shows approx. 0 Ohms:
- Check the leads between the OBD II DLC's connector 7 and the Motronic Engine Control Module's ECM B36, as well as DLC A connector 6 and ECM B22 on the AW TCM for signs of short circuiting to ground.
- After rectification: Check the OBD II communication lead (TCM).
If the ohmmeter shows infinite resistance:
- Check the lead between the OBD II DLC's connector 7 and the Motronic Engine Control Module B36 for signs of a break.
- After rectification: Check the OBD II communication lead (TCM).





Checking the OBD II Communication Lead (TCM)
^ Ignition OFF.
^ Connect the AW TCM.
^ Disconnect the Motronic control module.
^ Connect an ohmmeter between the OBD II DLC's connector 7 and ground.

The ohmmeter should show 90 - 110K Ohms.

If the reading is OK:
- The OBD II DLC is OK.
If the reading differs:
- Check the lead between the OBD II DLC's connector 7 and AW TCM B22 for signs of a break.