Audi Workshop Service and Repair Manuals

Removing and installing engine control unit

The multi-pin connectors of the engine control unit are enclosed in a protective housing, which is secured by a locking device and shear bolts -arrows-. To make it more difficult to unscrew the shear bolts, the threads have additionally been coated with locking fluid. The protective housing has to be removed before multi-pin connectors can be unplugged from engine control unit (e.g. to connect test box or renew engine control unit). Special tools and workshop equipment required

t  Hot air blower (from wiring harness repair set -VAS 1978-) t  Nozzle for hot air blower from the wiring harness repair set -VAS 1978- t  Vice-grip pliers (commercially available)

Removing –  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, remove nuts and take off wiper arms.

–  Unclip washer jets -arrow-. –  Push washer jet through assembly opening back into plenum chamber, leaving hoses connected.

–  Pull off rubber seal -1- on plenum chamber cover. –  Detach plenum chamber cover -2-.   Caution 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 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 Parts of the protective housing will become very hot as a result of heating the shear bolts. Take care to avoid burns. Try to ensure that only the thread is heated and none of the nearby components. These should be covered if necessary.

–  Carry out the following operations on the two shear bolts -arrows-, one after the other. –  Place the nozzle of the hot air blower close to the shear bolt on the protective housing. –  Switch on the hot air blower and heat the bolt for approximately 20 ... 25 seconds. –  Then grasp the bolt head with the vice-grip pliers and unscrew the shear bolt. –  Take off the protective housing.

–  Release and unplug front multi-pin connector -2- on engine control unit. –  Release retaining clip -arrow-. –  Pull engine control unit -1- out of bracket. –  Release and unplug rear multi-pin connector on 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. Installing Installation is carried out in the reverse order; note the following: –  Reinstall the engine control unit into the protective housing. –  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. After installing a new engine control unit, the following operations must be performed: –  Activate engine control unit in “Guided Fault Finding” under diagnosis option “Replace engine control unit” → Vehicle diagnosis, testing and information system VAS 5051.