Test Point 17 - Oxygen Sensor Function
TEST POINT 17 - DME 944 TurboOxygen Sensor Function (USA Cars and Unleaded Engines M 298/M 299)
A) Fast Test
(Engine at Operating Temperature, Correct Idle Speed)
Connect CO tester on test pipe in engine compartment on right-hand side. Disconnect oxygen sensor plug. Note CO value.
Pull off and plug vacuum line on fuel pressure regulator.
CO level must rise!
Connect oxygen sensor plug.
CO level must drop to specified value: 0.6 ± 0.2 %.
If there is no CO level change, the oxygen sensor or DME control unit is faulty.
B) Checking DME Control Unit
(Engine at Operating Temperature, Correct Idle Speed)
Connect CO tester on test pipe in engine compartment on right-hand side. Disconnect oxygen sensor plug. Check CO level.
Bridge oxygen sensor plug term. 1 (green) - sleeve contact - (wire harness to control unit) and ground with a piece of wire.
CO level must rise!
If CO level does not change, check power flow from wire plug term. 1 (green) to control unit term. 24 before replacing the DME control unit.
C) Checking Oxygen Sensor (V)
(Engine at Operating Temperature, Correct Idle Speed)
Disconnect oxygen sensor plug. Connect digital voltmeter between ground and term. 1 (pin contact) of sensor plug.
Display: approx. 0.1 - 1.0 V.
Note: DME control unit will switch off oxygen sensor control during the following operating conditions.
1. Coolant temperature below 15 °C and engine running with open idle contact.
2. Coolant temperature below 45 °C and engine running at idle speed.
3. Throttle full load contact closed or terminals B and C on test socket bridged and engine running at speed of > 3600 rpm.