Audi Workshop Service and Repair Manuals

Removing and installing engine control unit - engine codes AVB, AVF and AWX The following description applies to an engine control unit with protective housing. If an engine control unit without protective housing is fitted it is not necessary to perform the following operations.   Note

t  The engine control unit -1- is bolted via a locking plate -2- to protective housing -4-. To make it more difficult to unscrew the shear bolts -3-, the threads have additionally been coated with locking fluid. t  Engine control unit must be separated from protective housing before the connectors can be unplugged from the engine control unit (e.g. to connect the test box or renew the engine control unit). 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  Vice-grip pliers -3- (commercially available)

Removing –  When renewing engine control unit, select diagnosis object „Renew engine control unit“ in „Guided Fault Finding“ → Vehicle diagnostic tester. –  Switch off ignition and remove ignition key. –  Detach rubber seal from plenum chamber cover in direction of -arrow-. –  Detach plenum chamber cover -1- towards the front.

–  Lever off both cover caps -3- with a screwdriver. –  Loosen hexagon nuts -4- several turns. –  Loosen wiper arms -2- from wiper shafts by tilting slightly. –  Completely remove hexagon nuts and take off wiper arms. –  Pull off retaining clips -1- and detach cowl panel grille -5-.

–  Remove cover for electronics box in plenum chamber -arrows-. –  Carefully lever out the retaining strap using a screwdriver -arrow- from engine control unit with protective housing -4-.

–  Turn engine control unit -1- with protective housing -4- towards engine compartment so that locking plate -2- becomes visible. –  Place a clean cloth beneath the engine control unit for protection.   WARNING The following procedure must be followed exactly to prevent any damage (burning) to wiring, connectors, insulation and control units. Observe operating instructions for hot air blower.

–  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“.   Note Then use hot air blower to heat the thread of the locking plate into which shear bolts have been screwed. This step reduces inhibiting action of locking fluid on shear bolt threads and makes it easier to unscrew these bolts.   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.

–  Direct nozzle -1- of hot air blower towards thread of locking plate to enable nozzle to „surround“ thread. Allow nozzle to rest on upper end of metal housing. –  Switch on hot air blower and heat thread for about 20 to 25 seconds.

–  Then grasp head of bolt -2- with vice-grip pliers -1- and unscrew shear bolt in direction of arrow. –  Repeat the procedure for the second shear bolt. Be particularly careful here, as this shear bolt is in the immediate vicinity of control unit connector. Engine control unit can now be separated from protective housing. –  Release multi-pin connectors and disconnect from engine control unit.   Note When the connectors are disconnected from the engine control unit, the learnt values are erased but the contents of the fault memory remain intact. –  Remove engine control unit. Installing Installation is carried out in the reverse order; note the following: –  Protective housing must be screwed back on engine control unit. –  Clean threaded holes for shear bolts to remove any residue from locking fluid. This can be done using a thread tap. –  Use new shear bolts. –  Activate engine control unit in „Guided Fault Finding“ under diagnosis option „Replace engine control unit“ → Vehicle diagnostic tester.