Renewing engine control unit J623 — AUDI

Renewing
engine control unit
J623
Note
When the engine control unit is disconnected, the learnt values are erased but the contents of the fault memory remain intact.
Removing
Special tools and workshop equipment required
Hot air blower
1
from the
wiring harness repair set
VAS 1978
Nozzle attachment
2
from the
wiring harness repair set
VAS 1978
Commercially available vice-grip pliers
Vehicle diagnostic, testing and information system
VAS 5051B
Connect
vehicle diagnostic, testing and information system
VAS 5051B
and select vehicle system
“01 - Engine electronics”
from list. When doing this, the ignition must be switched on.
The display on
vehicle diagnostic, testing and information system
VAS 5051B
will show the control unit identification and the coding
2
.
Always start by displaying the control unit identification and printing it out.
Switch off ignition.
Remove cover from plenum chamber (right-side).
Unscrew both bolts
arrows
and remove the engine control unit towards front.
To help prevent unauthorised access to the connectors on the engine control units, the engine control unit
1
is bolted to a protective casing
4
by means of shear bolts
3
and a locking plate
2
.
To make it more difficult to unscrew the shear bolts, their threads have been coated with locking fluid.
Engine control unit must be separated from protective housing before connectors can be unplugged from engine control unit (e.g. when connecting test box or replacing engine control unit). This procedure is described in the following.
Procedure:
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.
Tilt engine control unit with protective housing towards engine compartment so that locking plate (item
2
in Fig.) 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
The shear bolts and protective housing also become very hot when heating the threads of the locking mechanism. 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 so that the nozzle
“surrounds”
the 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 insert new one.
Installing
Installation is performed accordingly in the reverse sequence.
Make sure you fit protective housing back on
engine control unit
J623
.
Always use new shear bolts.
The following steps must be performed after installing new engine control unit:
If
engine control unit
J623
is being renewed, select function
“J623 replace, further steps”
in
“Guided Fault Finding”
.