Test Point 12 - Knock and Charging Pressure Control

TEST POINT 12 - DME 944 Turbo

Knock and Charging Pressure Control

If a fault is assumed in the knock or charging pressure control, it can be identified with help of a flashing code (description - 1985 Model 944 Turbo Brochure).

Caution! The test should be made immediately after a test drive, since the memory will be cancelled after turning off the ignition.




Connect test adapter (P 9246) in the test socket and observe the flashing code.

Flash Code 1-2
Fault Battery voltage too low (less than 10.2 V)
Possible Cause Power supply (alternator, regulator, battery)

Flash Code 2-1
Fault Knock sensor Monitor
Possible Cause Plug loose
Wire break
Sensor faulty
Test Point/Check Knock sensor.
Connect ohmmeter on term. 11 and 13 of disconnected KLR control unit plug.
Display: 270-330k-ohms.
If 0 or inf. ohms are displayed, check wire connections or replace sensor if necessary.
Check for correct torque. 11 Nm.
Use original screw without a washer!

Flash Code 2-3
Fault Control unit faulty
Test Point/Check Replace control unit.

Flash Code 3-1
Fault Charging pressure too low
Possible Cause Charging pressure
Test Point/Check Check charging pressure.



Connect pressure tester (P 9103/2) on vacuum connection for pressure damper and place in car.
Test Value: 0.70 bar at 3000 rpm and full load (in 3rd gear).

Possible Cause Plug has fallen off of timing valve.
Wire break.
Timing valve faulty.
Test Point/Check Timing valve



a) Power supply
Connect voltmeter on red/green wire of timing valve plug and ground.
Display: battery voltage.
No display: perform test point 2.
b) Pull off coil resistor from timing valve plug on timing valve.
Connect ohmmeter on both connectors.
Display: 30 ohms.
c) Check power flow in wire from KLR control unit plug term. 2 to timing valve.
Replace KLR control unit, if everything is okay.

Possible Cause Vent line to solenoid valve plugged.
Test Point/Check Check flow.

Possible Cause Exhaust leak.

Possible Cause Leak in intake.
Test Point/Check See Test Point 14.

Possible Cause No pressure on bypass valve.
Test Point/Check Check activation or operation of bypass valve. Bypass valve must open with vacuum.

Possible Cause Break in pressure hose to KLR control unit (no pressure display).
Test Point/Check Check flow or for leaks.

Possible Cause Charging pressure control valve seized in open state.
Test Point/Check Check charging pressure control valve. The exhaust should be cold to check this control valve.
Disconnect pressure hose on charging pressure control valve and connect pressure pump (VAG 1274).
Start engine.




The exhaust pipe (arrow), leading to the charging pressure control valve, must heat up after a short time.
The pipe (large arrow) leading away from the charging pressure control valve must remain cold (charging pressure control valve closed).
Now supply 0.6 bar pressure to the charging pressure control valve; now the pipe leading away from the charging pressure control valve must heat up (control valve opened).

Possible Cause Turbocharger faulty.
Test Point/Check Check turbocharger.

Possible Cause Exhaust "closed" (with catalytic converter).
Test Point/Check Connect pressure tester (P910312) on exhaust test pipe.
Test value: 3500 rpm.
Full load 800 ± 100 mbar for 700 mbar charging pressure.

Possible Cause Throttle valve does not open fully.
Test Point/Check Adjust, if applicable.

Flash Code 3-2
Fault Charging pressure too high
Possible Cause Timing valve always has electric current.
Test Point/Check Timing Valve
a) Power supply
Connect voltmeter on red/green wire of timing valve plug and ground.
Turn on ignition.
Display: battery voltage.
No display: test point 2.
b) Pull off coil resistor from timing valve plug on timing valve. Connect ohmmeter on both connectors.
Display: 30 ohms.
c) Pull off plug on timing valve.
Connect test lamp on plug contacts. Turn on ignition. Test lamp must not come on.
Replace KLR control unit, if everything is okay.

Possible Cause Break in line to timing valve or to charging pressure control valve.
Test Point/Check Check flow or for leaks.

Possible Cause Timing valve inlet (orifice) plugged.
Test Point/Check Check flow.

Possible Cause Charging pressure control vaive is seized in closed state.
Diaphragm leaks.
Test Point/Check Check charging pressure control valve. Exhaust should be cold to check this control valve. Disconnect pressure hose to charging pressure control valve and connect pressure pump (VAG 1274).
Start engine.




The exhaust pipe (arrow), which leads to the charging pressure control valve, must heat up after a short time. The exhaust pipe (large arrow), leading away from the control valve, must remain cold (charging pressure control valve closed).
Now supply 0.6 bar pressure to the charging pressure control valve; the exhaust pipe leading away from the control valve will heat up (charging pressure control valve open).

Flash Code 3-3
Fault Pressure sensor faulty.
Test Point/Check Replace KLR control unit.

Flash Code 4-1
Fault Throttle valve potentiometer.
Possible Cause Power supply wire to potentiometer grounded out.
Test Point/Check See test point 9.

Possible Cause Plug fallen off.
Test Point/Check See test point 9.

Possible Cause Potentiometer faulty.
Test Point/Check See test point 9.

Flash Code 4-2
Fault Throttle valve potentiometer.
Possible Cause Break in wire to potentiometer.
Test Point/Check See test point 9.

Possible Cause Potentiometer faulty.