Component Tests

There is no separate piece of equipment to test the function of the Transmission Control Unit (TCU) controlling the AW4 automatic transmission. The condition of the TCU is determined by the elimination of other potentially defective components or wiring faults in a specific circuit. Even though the TCU is faulted by process of elimination, it should not be replaced until it has been retested after some basic screening procedures have been performed.

Most electrical/electronic devices are incorrectly diagnosed as faulty due to problems with connectors, even though the actual component or device is operating properly. Aside from the possibilities of poor mechanical connection between components and harnesses, poor contact is frequently the consequence of the insulating properties of surface oxides and other contaminants. Often the mere act of disconnecting and re-connecting a component will abrade contact points sufficiently enough to provide for proper conductivity between mating connectors.

Before a TCU is replaced, all other components and wiring relevant to a circuit must be examined by following the directives outlined in a diagnostic fault tree. If the TCU is suspect:

1. Carefully disconnect the TCU from the harness it it has not already been done.
2. Inspect the harness connector and the TCU for foreign material on the connector pins. Wipe the connector pins with an appropriate contact cleaner to remove any contamination.
3. Inspect the TCU harness connector for bent or missing pins, broken wires, missing wires, improper or missing insulation, etc. Repair or replace as necessary.
4. Inspect the TCU for bent or missing pins. Repair or replace as necessary.
5. Carefully reconnect the TCU to the harness and retest the vehicle with the DRBII.
6. If the vehicle does NOT PASS the test and failed with the SAME FAULT and number, replace the TCU.