Audi Workshop Service and Repair Manuals

Renewing engine control unit   Note Not every engine control unit is bolted to a protective housing. Whether a protective housing is fitted depends on the engine/gearbox combination. 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  The engine control unit is bolted to its protective housing. To make it more difficult to unscrew the shear bolts for the locking plate, the threads have additionally been coated with locking fluid. t  The metal casing 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 remove ignition key.

–  Pull rubber seal -1- off plenum chamber cover towards front. –  Detach plenum chamber cover. –  Remove both windscreen wiper arms -2- (mark their positions). –  Unclip plenum chamber cover - arrows-.

–  Remove cover for engine control unit.

–  Carefully lever off retaining strap with a screwdriver -arrow-. Work steps if no protective housing is fitted:

–  Release retaining tabs -arrows- and unplug connectors -1- and -2- from engine control unit. –  Take out old engine control unit and install new one. Work steps if a protective housing is fitted:

–  Carefully lever off retaining strap with a screwdriver -arrow-.   Note Item -1- in illustration: engine control unit with protective housing

To help prevent unauthorised access to the connectors on the engine control unit, the engine control unit -1- is bolted to a protective housing -4- by means of a locking plate -2- and shear bolts -3-. To make it more difficult to unscrew the shear bolts, their threads have been coated with locking fluid.   WARNING The following procedure must be followed exactly to prevent any damage (scorching) to wiring, connectors, insulation and control units. Observe operating instructions for hot air blower.

–  Tilt engine control unit with protective housing towards engine compartment so that locking plate (item -2- in illustration) becomes visible; place a clean cloth beneath engine control unit with protective housing.

–  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 thread of locking plate, into which shear bolts are 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 protective 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. The procedure for the second shear bolt is exactly the same. Take particular care here to avoid the control unit connectors in the immediate vicinity.

–  Direct nozzle -1- of hot air blower towards thread of locking plate again to enable nozzle to „surround“ thread. Allow nozzle to rest on upper end of protective 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. Engine control unit can now be separated from protective housing. –  Release connectors on engine control unit and unplug connectors. –  Take out old engine control unit and install new one. Installing Installation is performed in the reverse sequence. –  Make sure you fit protective housing (if fitted) 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. –  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“.