20V Motronic ECU System Component Operation
1991 200TQ with 20V Turbo Engine
1992-95 S4/S6 with 20V Turbo Engine
Engine Control Unit (ECU)
Vacuum/Boost line
In order for the ECU to work correctly, it must receive an accurate
pressure signal (vacuum or boost) from the intake manifold. There is
a plastic line with rubber hoses on each end connected from the ECU
to the intake manifold.
The vacuum/boost line (Green plastic line and rubber hose) from the
intake manifold to the ECU should be checked for leaks if you are getting
too much boost or a fault code 2221, 2222 or 2224. You can connect a
hand vacuum pump to the line after removing it from the back of the
intake manifold and see if it holds vacuum. If you have access to compressed
air and have an accurate pressure regulator, you can apply 15-20 psi
to the vacuum/boost line and listen for any leaks.
If you turn on the ignition, (Don't start the engine) you can read the
boost pressure off the digital instrument panel boost pressure display,
and see if it corresponds to the actual pressure applied to the ECU
line from the air pressure regulator.
BE CAREFUL WHEN APPLYING PRESSURE TO THIS LINE, DO NOT EXCEED 20 PSI
OF PRESSURE OR THE INTERNAL ECU PRESSURE SENSOR COULD BE DAMAGED
On the 1991 200TQ 20V, there is a plastic moisture trap (clear fuel
filter) installed in the vacuum/boost line about a foot before where
the line connects to the ECU. The 20V Motronic ECU is located underneath
the passenger lower right kick panel cover.
The 1992-95 S4/S6 also has a moisture trap, but it is located underneath
the rear black plastic cover in the engine compartment. Many times the
hose blows off this plastic moisture trap and can cause the car to go
into limp home mode with low boost and poor running.
References: [1] Audi of America service training publication:
"The New 20V Turbo Engine for the Audi 200 Quattro-publication All rights
reserved.
Copyright © SJM Autotechnik™ , all rights reserved
Return to Troubleshooting Tips page.
Return to SJM Autotechnik™ main page.
