Audi Workshop Service and Repair Manuals

Removing and installing 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  Small, commercially available mole grips -3-   Note t  Not every engine control unit is bolted to a protective housing. Whether a protective housing is fitted depends on the engine/gearbox combination.

t  The engine control unit -1- is bolted to the protective housing -5-. To make it more difficult to unscrew the shear bolts -4- for locking plate -2-, their threads have been coated with locking fluid. t  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 –  Before removing the engine control unit -J623-, the adaption values of the injectors and the ash deposit mass must be read out. Use → Vehicle diagnostic tester. –  Store adaption values as electronic file. –  Switch off ignition and remove ignition key after storing electronic file containing adaption values.   Note If the adaption values of the injectors cannot be read out of the old (defective) engine control unit, they must be entered into the new engine control unit manually and the adaption procedure must be performed accordingly.

–  Remove nut -3- and bolt -2-. –  Pull filler neck -1- with filler pipe out of washer fluid reservoir and through opening in body -arrow-.

–  Unscrew bolts -arrows- and take off cover for electronics box.   Note Disregard -item 1-.

–  Release retainers -arrows A- and pull out engine control unit -J623--arrow B-.   Note Cover painted surfaces with a cloth to prevent scratching.

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.

Switch on the hot air blower and heat the bolt for approximately 20 ... 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 should be removed without being heated. –  Detach protective housing from control unit connectors. –  Release connectors on engine control unit and unplug connectors. –  Take out old engine control unit -J623- and install new engine control unit -J623-. Installing Installation is performed in the reverse sequence. –  After installation, the protective housing 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 using → Vehicle diagnostic tester in „Guided Functions“ mode, „Replace engine control unit“.