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-   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 –  When renewing engine control unit, select diagnosis object „Replace engine control unit“ in „Guided Functions“. –  Switch off ignition and take out ignition key. –  Remove air cleaner housing.

–  Release fasteners -arrows- and detach engine control unit -J623- from bracket.   Note

t  The threads of the two shear bolts -4- which are not screwed into the engine control unit -1- are secured with locking fluid. To unscrew these two bolts, the threads must therefore be heated with the hot air blower. t  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.

Caution Wiring, connectors, insulation and control units can be burnt and damaged. Keep exactly to the following procedure. Observe operating instructions for hot air blower. –  Select settings on hot air blower -4- as shown in illustration: 2 -  Temperature potentiometer to maximum heat output 3 -  Two-stage air flow switch to position „3“   Note t  Then use hot air blower to heat threaded holes in protective housing into which shear bolts have been screwed. This reduces the inhibiting action of the locking fluid on the shear bolt threads and makes it easier to unscrew these bolts. t  Cover up all painted parts to avoid any damage caused by hot air blower or vice-grip pliers.   WARNING Risk of burns. Parts of the metal locking plate will become very hot as a result of heating the shear bolts. Try to ensure that only the thread is heated and none of the nearby components. These should be covered if necessary.

–  Attach shrink element for hot air blower -VAS 1978/15A- to hot air blower -VAS 1978/14A-. –  Hold shrink element on hot air blower close to shear bolt on protective housing. –  Switch on hot air blower and heat bolt for 20 ... 25 seconds.

–  Then grasp bolt head with vice-grip pliers and unscrew shear bolt. –  Repeat procedure for second shear bolt. –  Detach protective housing from multi-pin connectors. –  Unscrew the two shear bolts screwed into the engine control unit (they do not need to be heated). Installing Installation is carried out in the reverse order; note the following: –  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 via a vehicle diagnostic tester in „Guided Functions“ mode, „Replace engine control unit“.