Test point

Speed signal/ Using System Tester 9288, the speed signal may be read directly in

Speedometer the Actual values menu item. As an alternative, check with an oscillo-

Fault code 1 19 scope.

To do so, connect oscilloscope to terminal 9 and terminal 24 of the control unit plug. Turn left front wheel manually. The following signal must now be displayed:

Fault, Fault Code Possible Causes, Elimination, Remarks Test point 7

Air flow Voltage supply (V)

sensor (V/Q) Disconnect plug at air flow sensor, connect voltmeter to plug ter-

Fault code 121 minais 2 and 5 using test leads.

Ignition on:

Display: Voltage approx. 10 Volt up to 13.8 Volt

No display: check in accordance with wiring diagram Reconnect plug.

Checking the hot-wire signal with System Tester 9288

The air flow sensor signal may be tested directly in the Actual values menu item using System Tester 9288. To check the signal, remove upper air cleaner section and start engine.

Blow against hot wire. This must cause the System Tester display to change.

Fault, Fault Code Possible Causes, Elimination, Remarks

Checking the hot wire signal (V)

Connect plug to air flow sensor. Pull off DME plug.

Connect DME plug terminal 36 to ground (e.g. door stop). Connect Voltmeter to DME plug terminal 7 and 26.

Blow against air flow sensor and observe voltmeter. A voltage change must occur (-1.6-5 V).

Checking the hot-wire burn-off circuit (visual check)

Operate engine with air flow sensor installed and connected. When an engine temperature > 60' C is reached, increase engine speed to above 2,000 rpm and stop engine

(ignition off).

After a waiting time of approx. 4 seconds, the hot wire must glow for approx. 1 second (burn-off).

Test point 8 Oxygen regulation stop

Fault code 1 23

The oxygen regulator cannot operate within its control range if extreme problems of mixture preparation occur, e.g. due to an excessively lean setting because of unmetered air, or due to an excessively rich setting because of a faulty injector valve. The oxygen regulator then moves up to the stop position.

Oxygen regulation stop too rich:

Oxygen regulation stop too lean:

Check intake system for leaks (Test point 29)

Check fuel pressure (Test point 28) Check injector valves for leaks

Fault, Fault Code Possible Causes, Elimination, Remarks

Checking the sensor signal

Using the System Tester 9288, the oxygen sensor signal may be read directly under the Actual values menu Item. Diagnosis can only be carried out if an engine temperature of 70 deg. C has been reached for more than 1 minute.

If not:

Disconnect oxygen sensor plug. Connect digital voltmeter with test connector (sensor voltage signal) and ground at the sensor end.

Start engine and allow to warm up so that the oxygen sensor reaches its operating temperature. When the mixture is enriched, e.g. acceleration, a change in the voltage signal must be displayed.

Voltmeter display:

approx. 150 mV - 900 mV (acc. to mixture composition) If the regulator sets in with a certain delay, the oxygen sensor heater must be checked. To do so, connect voltmeter at control unit end with sensor plug disconnected and engine running. System voltage must be present.

Test point 9

Oxygen sensor (V)

(Sensor signal) Fault code 1 24

Test connection:

1 = Sensor voltage

2 = Sensor heating

3 = Sensor heating Note:

If the control unit detects an oxygen sensor voltage signal of more than 1.4 V or less than 0.1 V, the control unit switches to operation without oxygen sensor. (Short to ground or open circuit)

If regulation does not work and the sensor voltage is O.K., check the coding of the control unit before replacing it.

Do It Yourself Car Diagnosis

Do It Yourself Car Diagnosis

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    What causes oxygen regulation stop fault code?
    6 years ago

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