Oxygen Sensor: Testing and Inspection

1. Connect a dwell or duty cycle meter (Siemens 451 or equivalent) to oxygen sensor test connection located near the right strut tower in the engine compartment. Connect the positive lead to the blue/white wire, and the negative lead to ground.
2. Disconnect coil wire from distributor cap and connect to ground.
3. Remove fuel pump relay from fuse panel and install jumper wire US 4480/3 or equivalent, ensuring that switch is in off position.
4. Turn jumper wire switch on. If frequency valve makes buzzing sound, proceed to step 12. If not, proceed to step 5.
5. Disconnect electrical connector at frequency valve.
6. Check contact pins and socket of frequency valve for proper position and damage, repairing as necessary.
7. Connect test light across terminals of frequency valve.
8. If test light does not illuminate, check wiring of frequency valve and voltage supply of oxygen sensor relay and control unit.
9. If wiring and voltage supply are satisfactory, replace oxygen sensor relay.
10. If test light still does not illuminate, replace control unit.
11. Connect ohmmeter across terminals of frequency valve. If ohmmeter does not read 2-3 ohms, replace frequency valve.
12. Disconnect electrical connector at thermo switch and ensure that tester reading is 48-52% steady.
13. Connect jumper wire across terminals of thermo switch electrical connector.
14. If tester does not read 78-82% and steady, check wiring and repair as necessary.
15. If wiring is satisfactory, replace control unit.
16. Remove jumper wire at electrical connector.
17. Connect ohmmeter across terminals of thermo switch. If ohmmeter does not read infinite ohms with thermo switch temperature above 30°C (86°F), and zero ohms with thermo switch temperature below 20°C (68°F replace thermo switch.
18. Depress full throttle switch. If tester reads 63-67%, proceed to step 23. If not, proceed to step 19.
19. Check wiring of full throttle switch, repairing as necessary.
20. Disconnect electrical connector at full throttle switch.
21. Connect ohmmeter across terminals of full throttle switch.
22. If ohmmeter does not read infinite ohms with full throttle switch not depressed and zero ohms with full throttle switch depressed, replace full throttle switch.
23. Crank starter.
24. If tester does not read a constant 78-82%, check wiring to start-enrichment relay and hot-start pulse relay, replacing relay(s) as necessary.
25. If wiring is satisfactory, replace control unit.
26. Disconnect electrical connector at oxygen sensor and connect green wire to ground.
27. If tester does not read at least 87%, check wiring.
28. If wiring is satisfactory, replace control unit.
29. Connect green wire to positive terminal of 1.5 volt "D" battery and connect battery negative terminal to ground.
30. If tester does not read less than 20%, check wiring.
31. If wiring is satisfactory, replace control unit.
32. Disconnect crankcase breather hose at cylinder head cover and plug hose.
33. Connect electrical connector at oxygen sensor.
34. Connect coil wire at distributor cap.
35. Start engine and run at 2500 RPM for at least 2 minutes.
36. If tester reading does not fluctuate at idle speed, proceed as follows:
a. If reading is constant at approximately 13% or 87%, adjust CO level to specifications.
b. If reading is 50%, still not fluctuating, or constant at 13% or 87%, and control unit operates properly, replace oxygen sensor.
37. Connect electrical connector at thermo switch.
38. Connect crankcase breather hose at cylinder head cover.
39. Remove jumper wire.