DTC 45

Fig. 12 Oxygen sensor wiring circuit. 1984:

Fig. 13 Oxygen sensor wiring circuit. 1985:

When the oxygen sensor temperature is below 200° F, its output voltage will be .5 volts and the ECM will operate the system in the open loop mode. When the oxygen sensor temperature is above 200° F, the output voltage will vary between zero and one volt. When oxygen sensor output voltage begins to vary, the ECM will operate the system in the closed loop mode. Code 45 indicates that the oxygen sensor signal is above .5 volts and constant. If voltage remains in this high range, code 45 will be displayed and the system will operate in the open loop mode. This condition may be caused by the following:
a. Defective oxygen sensor.
b. Defective electrical connectors or wiring.
c. ECM not processing oxygen sensor signal.
d. Improper fuel delivery.

To diagnose a Code 45, proceed as follows:
1. Turn ignition on, enter diagnostics and display parameter .0.7.
2. Disconnect oxygen sensor electrical connector and note parameter value. If reading is greater than .57 volts, proceed to step 3. If reading is less than .57 volts, proceed to step 4.
3. Check circuit 412 for a short to voltage. If circuit is satisfactory, fault is in ECM or ECM connector. Repair or replace as necessary.
4. Connect jumper wire between oxygen sensor pins on ECM side to ground and note parameter value. If reading is less than .05 volts, proceed to step 5. If reading is greater than .05 volts, proceed to step 6.
5. Reconnect oxygen sensor and perform fuel delivery and oxygen sensor checks as described in this section. Also, check air cleaner for restrictions.
6. Check circuits 412 and 413 for an open. If circuits are satisfactory, fault is in ECM or ECM connector. Repair or replace as necessary.