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Replacing Motronic control unit -J220 > < Checking injection quantity, freedom from leaks and spray pattern of injectors

A4 Cabriolet Mk2

Motronic injection and ignition system (8-cyl.)
Servicing Motronic injection system
Wiring and component check using test box V.A.G 1598/31
 
W00-0943

Notes:

  • ◆ → Test box V.A.G 1598/31 is designed for simultaneous connection to engine control unit wiring harness and actual engine control unit.
  • ◆ The advantage of this is that the electronic engine management system remains fully operational with the test box connected (e.g. measurement of signals with engine running).
  • ◆ Whether or not the engine control unit is additionally to be connected to the test box is indicated in the appropriate test sequences.
  • ◆ Always use test leads from adapter set V.A.G 1594 for connection of testers to test box V.A.G 1598/31.
Attention:
So as not to destroy electronic components, select required measuring range before connecting test leads and observe test conditions.

Connecting up test box V.A.G 1598/31

  • ‒ Switch off ignition.
 
A27-0088
  • ‒ → Detach rubber seal of plenum chamber cover in direction of arrow.
  • ‒ Detach plenum chamber cover -1- to front.
 
A20-0833
  • ‒ → Use screwdriver to prise off the two caps -3-.
  • ‒ Slacken off hexagon nuts -4- by several turns.
  • ‒ Detach wiper arms -2- from wiper shaft by tilting slightly.
  • ‒ Completely unscrew hexagon nuts and detach wiper arms.
  • ‒ Pull off securing clips -1- and detach cowl panel grille -5-.
 
A10-0996

  • ‒ → Remove cover for electronics box in plenum chamber -arrows-.
 
A24-0483
  • ‒ → Use screwdriver to carefully prise off fastener -arrow-.

Note:

Item -1- in illustration shows engine control unit with protective enclosure.
 
A24-0477

→ To render access to the connectors on the engine control unit more difficult, the engine control unit -1- is bolted by way of a catch -2- and shear bolts -3- to a protective enclosure -4-.

Locking fluid is applied to thread of shear bolts to make bolts more difficult to screw out.

Engine control unit must be separated from protective enclosure to unplug connectors from engine control unit (e.g. when connecting up test box or replacing engine control unit). This procedure is described in the following.

Tools required:
 
A24-0475
  • ◆ → Hot-air blower -1- (from wiring-harness repair set VAS 1978)
  • ◆ Nozzle attachment -2- (also from wiring-harness repair set VAS 1978)
  • ◆ Commercially available gripping pliers

Procedure:

Attention:
To avoid damaging (scorching) wires, connectors, insulation and control units, always adhere exactly to the following operations and observe operating instructions for hot-air blower.
 
A24-0477
  • ‒ → Tilt engine control unit with protective enclosure towards engine compartment so that catch (item -2- in Fig.) becomes visible and place a clean cloth beneath engine control unit with protective enclosure.
 
A24-0476
  • ‒ → Make settings on hot-air blower as shown in illustration, i.e. set temperature potentiometer -2- to max. heat output and two-stage air flow switch -3- to position 3.

Note:

Then use hot-air blower to heat thread of catch into which shear bolts are screwed. This operation is designed to reduce the inhibiting action of the locking fluid on the shear bolt thread to make it easier to screw out the shear bolts afterwards.

Attention:
Heating the thread of the catch also greatly increases the temperature of the shear bolts and protective enclosure components. 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).
 
A24-0478
  • ‒ → Move nozzle -1- of hot-air blower towards thread of catch such that nozzle "surrounds" thread. Allow nozzle to rest on upper end of protective enclosure.
  • ‒ Switch on hot-air blower and heat thread for roughly 20 to 25 seconds.
 
A24-0481
  • ‒ → Then grasp head of bolt -2- with gripping pliers -1- and screw out shear bolt in direction of arrow.

Employ exactly the same procedure for the second shear bolt, taking particular care to avoid the control unit connectors in the immediate vicinity.
 
A24-0479
  • ‒ → Move nozzle -1- of hot-air blower towards thread of catch again such that nozzle "surrounds" thread. Allow nozzle to rest on upper end of protective enclosure.
  • ‒ Switch on hot-air blower and heat thread for roughly 20 to 25 seconds.
 
A24-0480
  • ‒ → Then grasp head of bolt -2- with gripping pliers -1- and screw out shear bolt in direction of arrow.

Engine control unit can now be separated from protective enclosure.

  • ‒ Release connectors of engine control unit and unplug.
 
A24-0270
  • ‒ → Connect test box V.A.G 1598/31 to wiring harness connector. Earth clip -arrow- must be connected to earth. Whether or not engine control unit is additionally to be connected to test box is indicated in the appropriate test sequences.
  • ‒ Perform testing as described in appropriate repair operations.

Installing engine control unit

Install accordingly in reverse order of removal; protective enclosure is always to be refitted to engine control unit. New shear bolts must be used.

  • ‒ Interrogate and if necessary erase fault memory.

=> Vehicle diagnostic, testing and information system VAS 5051

Replacing Motronic control unit -J220 > < Checking injection quantity, freedom from leaks and spray pattern of injectors