DTC 13

Fig. 26 ECM installation:

Fig. 45 Checking oxygen sensor signal. 1987 - 88 models:

Diagnostic Code 13, Circuit Check
If oxygen sensor fails to send signals to the ECM, the feedback system will not operate. 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 4 (oxygen sensor signal) and 9 (ground), Fig. 45.
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. Leaking intake system or faulty carburetor causing lean mixture.
c. 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 coolant temperature sensor.
c. Defective wide open throttle switch.
d. Disconnected mixture control solenoid wire.
6. After checking, install ECM into instrument panel, and check for secure connection of ECM connector.



Diagnostic Code 13, O2 Sensor Check
1. Start and operate engine until coolant reaches normal operating temperatures.
2. Disconnect oxygen sensor electrical connector, then connect a suitable voltmeter between disconnected connector and body ground.
3. With engine RPM operating at 1500 - 2000 RPM, turn wide open micro switch ``On'' by moving throttle lever down. Voltmeter reading should indicate approximately .8 volts.
4. With engine operating at 1000 - 1500 RPM, disconnect vacuum hose at intake manifold next to EGR valve. Voltmeter reading should indicate almost ``0'' volts.
5. If oxygen sensor is malfunctioning, replace with a new one. When installing new oxygen sensor, torque to 33.0 - 39.5 ft. lbs.
6. Reconnect vacuum hose.