Engine Controls - Checking Oxygen Sensor

91mitsubishi04

NO. TSB-91-13-004

DATE March, 1991

MODEL 1989-1990 Federal Trucks


SUBJECT: OXYGEN SENSOR CHECKING



PURPOSE

This bulletin supplies Service Technicians with oxygen sensor diagnosis information. On page 3 of this bulletin is a flow chart that should be used when diagnosing a suspected oxygen sensor malfunction including special steps for 1989 - 1990 Federal Trucks equipped with single-wire oxygen sensors.


GENERAL OXYGEN SENSOR INFORMATION

The oxygen sensor detects the concentration of oxygen in the exhaust gases, converting the concentration data into a constantly varying voltage. The sensor begins functioning at approximately 600~ F. Below 600~ F the voltage produced is not accurate. Therefore, it is necessary to warm up the engine to normal operating temperature (180 - 190~ F) before checking the voltage.

If the air-fuel mixture is richer than the optimum ratio, a voltage of up to approximately 1V is produced; conversely, if the air-fuel mixture is leaner than optimum, then the voltage approaches OV.

The electronic control unit interprets the oxygen sensor voltage and along with information from other inputs, regulates the amount of fuel injected. The oxygen sensor assists Air/Fuel ratio control only when the engine is warm. Its signal has no effect when cold and during warm-up.

If the oxygen sensor output voltage deviates from the standard value, and the diagnosis shows the is sensor is operating properly, the cause is probably a malfunction of a component related to air-fuel mixture ratio control and not the Oxygen Sensor itself.

For example:
Improper wiring connection.
Fuel injector malfunction.
Air leakage into the intake manifold.
Malfunction of the air-flow sensor, intake air temperature sensor, atmospheric pressure sensor, or water temperature sensor.


WARRANTY INFORMATION

Standard warranty procedures apply.


SPECIFIC DIAGNOSTIC INFORMATION

Refer to the applicable service manual for specific diagnostic information.

CAUTION: When performing specific service manual diagnostic inspections, use only a Digital Volt Ohm Meter.





PARTS INFORMATION

Ground Strap: MB542439

(For use on 1989 - 1990 Federal Trucks).





OXYGEN SENSOR DIAGNOSIS