Operational Check - Oxygen Sensor & Feedback System

Fig. 26 ECM installation:

Fig. 31 Oxygen sensor signal test:

Fig. 32 Feedback signal test:

If SENSOR light does not flash at 30,000 or 60,000 miles, or when cancel switch in fuse panel is turned on, check feedback system operation as follows:
1. Remove ECM from instrument panel, Fig. 26, leaving connector connected.
2. Start engine and allow to idle at normal operating temperature.
3. Connect voltmeter between terminals 10 (oxygen sensor signal) and 19 (ground), Fig. 31.
4. Between idling and 1500 - 2000 RPM, voltmeter needle should deflect between 0 and .8 volts. If voltmeter needle, indicates zero, check the following:
a. Oxygen sensor wire disconnected or making poor contact.
b. Vacuum leak or faulty carburetor causing lean mixture.
c. Pulse air or secondary air system constantly sending air to exhaust manifold.
d. Inner resistance of voltmeter is too low.
e. Defective oxygen sensor.
5. If voltmeter needle remains at .8 volt and does not deflect, check the following:
a. Choke operating because engine is not warmed up.
b. Defective thermal switch.
c. Defective wide open throttle switch.
d. Disconnected mixture control solenoid wire.
6. After confirming that oxygen sensor is properly signalling ECM, check feedback system as follows:
a. Connect positive lead of ohmmeter to body and negative lead to terminal 20, Fig. 32.Do not reverse connections, since damage to ECM may result.
b. Check that ohmmeter needle deflects, which means that ECM is sending feedback signal. Turn on cancel switch in fuse box to check if SENSOR lamp flashes. If not, check if bulb is burned out.
7. Reinstall ECM into instrument panel, making sure that connector is securely connected.