Test 1: Oxygen Sensor Testing
TEST 1: OXYGEN SENSOR HEATINGThis test only applies to heated oxygen sensors with 3-pin or 4-pin plug connector.
Note:
If an exhaust emission inspection was carried out beforehand, the engine must be allowed to cool to ambient temperature in order to carry out Test 1. If necessary start with Test 2.
There are two basic types of heated sensor circuits. The first type such as DME 1.7, turns the heater on as soon as the engine is started (as long as the engine was cold). The cold current should be approximately 4.0 amps. If operating properly the current will drop off to approximately 1.4 amps by the time the engine has reached normal operating temperature. If the sensor does not operate in this fashion it is defective.
The second type of sensor heating circuit such as DME 3.3 & 3.3.1 uses a delay. The time at which the heater circuit is turned on is determined by three factors.
1. Load
2. Temperature
3. Time
Varying any one of these will change the time at which the circuit is activated. Until the circuit is activated there will be no current. After activation the heating circuit should act the same as the DME 1.7 heater circuit.
This heated sensor circuit may be easily recognized by its utilization of an oxygen sensor heated relay. Consult your ETM for the location.
Disconnect plug-in jumper from simulator.
Note:
The plug-in jumper must be reconnected on completion of the test.
Select multimeter measuring range "A/DC" (Amp/direct current) so that at least 5 A can be measured.
Connect multi meter to the red "heating" sockets on the simulator.
Start engine.
Read out heater current on the multimeter until operating temperature
is reached.
The heating current drops during the engine heating-up phase.
Engine cold:
4.0 A +/- 0.30 A
Engine at operating temperature:
1.4 A +/- 0.15 A
Diagnosis:
Heating resistor of oxygen sensor OK.