Audi Workshop Service and Repair Manuals

Renewing engine control unit -J623- Special tools and workshop equipment required

t  Hot air blower -VAS 1978/14A--item 1- with nozzle attachment -2- from wiring harness repair set -VAS 1978 B- t  Mole grips (commercially available) -3- t  Vehicle diagnostic, testing and information system -VAS 5051B-

The engine control unit -1- is bolted to two metal locking plates -2 and 5-. To make it more difficult to unscrew the shear bolts -4- for locking plate -2-, their threads have been coated with locking fluid. The protective housing has to be removed before the connectors can be unplugged from the engine control unit (e.g. to connect the test box or renew the engine control unit). Removing –  When renewing engine control unit, select diagnosis object „Replace engine control unit“ in „Guided Functions“ on vehicle diagnostic, testing and information system -VAS 5051B-. –  Switch off ignition and remove ignition key. –  Lever off caps on windscreen wiper arms with a screwdriver.

–  Loosen hexagon nuts -arrows- several turns. –  Loosen wiper arms from wiper shafts by tilting slightly. –  Completely remove hexagon nuts and detach wiper arms from wiper shafts.   Note Use puller (commercially available) to remove wiper arms if necessary.

–  Pull off rubber seal -1- and remove plenum chamber cover -2-.

–  Release clip -arrow- and remove engine control unit -J623-.   Note Cover painted surfaces with a cloth to prevent scratching.

To help prevent unauthorised access to the connectors on the engine control unit, the control unit is secured by means of shear bolts to a locking plate or a metal casing.

The threads of the two shear bolts -4- which are not screwed into the engine control unit are secured with locking fluid. To unscrew these two bolts, the threads must therefore be heated with the hot air blower.

The threads of the two shear bolts -3- which are screwed into the engine control unit are not secured with locking fluid. Do not apply heat to the threads in the control unit housing; this is not necessary and would cause overheating of the control unit.

Select settings on hot air blower as shown in illustration, i.e. set temperature potentiometer -2- to maximum heat output and two-stage air flow switch -3- to position 3.   WARNING Heating the thread of the locking plate also heats up the shear bolts and parts of the metal housing. Take care to avoid burns. It is also important to ensure that only the thread is heated and none of the surrounding components if at all possible. These should be covered if necessary.

–  Apply heat to the threads of the shear bolts on the connector side for approx. 25 to 30 seconds. –  Unscrew shear bolts using suitable vice-grip pliers (see arrow in illustration).

–  The two shear bolts screwed into the engine control unit do not need to be heated. They can be removed without heating. –  Detach metal locking plate from control unit connectors. –  Release connectors on engine control unit -J623- and unplug connectors. –  Take out old engine control unit -J623- and connect new engine control unit -J623-. Installing engine control unit Installation is performed in the reverse sequence. –  After installation, the locking plate must be re-fitted on the engine control unit -J623-. –  Clean threaded holes for shear bolts to remove any residue from locking fluid. This can be done using a thread tap. –  Always use new shear bolts. After installing a new engine control unit, the following operation must be performed: –  Activate engine control unit via vehicle diagnostic, testing and information system -VAS 5051B- in „Guided Functions“ mode, „Replace engine control unit“.