Scan Tool Connecting

Wiring and Components, Checking with Adapter Cable VAG 1598/31

• The adapter cable. 121-pin (V.A.G 1598/31) is designed so that it can be connected to the ECM wiring harness and the ECM itself at the same time.





• This makes it possible for the electronic engine control to remain fully functional with the test box attached (e.g. measurement of signals with engine running).

• The procedures will indicate whether the engine control module is to remain connected to the test box or not.

• Use multimeter (V.A.G 1526C) and voltage tester (V.A.G 1527B) to check.

• To connect testing devices to the test box (V.A.G 1598/31), always use adapters from connector test set (V.A.G 1594C).

CAUTION!
To avoid damaging electronic components, switch to the corresponding measuring range and observe all test conditions before connecting the test leads.

- Switch ignition off.

- Remove right cover from plenum chamber.

- Loosen both bolts - arrows - and remove Engine Control Module (ECM) toward front.





To increase difficulty with which ECM connectors can be accessed, ECM - 1 - is secured in a protective housing - 5 - with retaining tabs - 2 - and shear bolts - 3 and 4 -.





The threads of the shear bolts have been coated with a locking compound, to further increase the difficulty of unscrewing the shear bolts.

To disconnect connectors from engine control module (ECM) (e.g. to connect the test box or to replace the ECM), the ECM must be separated from the protective housing. The procedure for this is as follows.

Procedure:

Special tools, testers and auxiliary items required

• Heat gun - 1 - (from wiring harness repair kit (VAS 1978))





• Nozzle attachment - 2 - (also from the wiring harness repair kit (VAS 1978))

• Commercially available locking pliers (vise grips)

CAUTION!
To prevent damages (burning) of wire and harness connections, insulation and control modules, perform the following work procedures exactly! Observe operating instructions for heat gun.

- "Flip" Engine Control Module (ECM) with protective housing in direction of engine compartment so that the locking mechanism (item - 2 - in illustration) becomes visible, place a clean rag below the Engine Control Module (ECM) with protective housing.





- Set adjustment on heat gun as shown in the illustration, with temperature potentiometer - 2 - set to maximum heat and the two-stage air flow switch - 3 - set to level 3.





• Finally, the locking mechanism thread into which the shear bolts are screwed is warmed with a heat gun. During this step, the holding effect that the locking compound has on the shear bolt threads is reduced, thereby allowing the shear bolts to be unscrewed easier.

CAUTION!
When heating threads of locking mechanism, snap-off screws and components of protective housing are also heated intensely. Do not burn yourself! Make sure that only the threads are heated as much as possible, and not any of the surrounding parts. Cover these parts if necessary.

- Guide air gun nozzle - 1 - onto locking mechanism thread so that the nozzle "encloses" the thread. Let nozzle make contact steadily on upper end of protective housing.





- Switch on heat gun and heat thread for approx. 20 to 25 seconds.

- Grab bolt head - 2 - with locking pliers - 1 - and turn shear bolt in direction of arrow.





The procedure for the second shear bolt is exactly the same. Be especially careful, because the control module connectors are located in the immediate vicinity.

- Guide air gun nozzle - 1 - against locking mechanism thread so that the nozzle "encloses" the thread. Let nozzle make contact steadily on upper end of protective housing.





- Switch on heat gun and heat thread for approx. 20 to 25 seconds.

- Grab bolt head - 2 - with locking pliers - 1 - and turn shear bolt in direction of arrow.





Then, the engine control module (ECM) can be separated from protective housing.

- Disengage connectors from Engine Control Module (ECM) and then disconnect connectors.

- Connect adapter cable, 121-pin (V.A.G 1598/31) to wiring harness connector. Ground (GND) clamp must be connected to Ground (GND). The procedures will indicate whether the engine control module is to be connected to the test box.





- Perform test as described in relevant repair sequences.

Installing engine control module (ECM)

Installation is performed in reverse order.

- Engine Control Module (ECM) (J623) must be installed again with protective housing.

- New shear bolts must always be used.