TESTING

WARNING
Do not pierce the wires when testing this sensor; this can lead to wiring harness damage. Backprobe the connector to properly read the voltage of the HO2S.

Single Wire Sensor

1. Start the engine and bring it to normal operating temperature, then run the engine above 1200 rpm for two minutes.
2. Backprobe with a high impedance averaging voltmeter (set to the DC voltage scale) between the oxygen sensor (02S) and battery ground.
3. Verify that the 02S voltage fluctuates rapidly between 0.40–0.60 volts.
4. If the 02S voltage is stabilized at the middle of the specified range (approximately 0.45–0.55 volts) or if the 02S voltage fluctuates very slowly between the specified range (02S signal crosses 0.5 volts less than 5 times in ten seconds), the 02S may be faulty.
5. If the 02S voltage stabilizes at either end of the specified range, the ECM is probably not able to compensate for a mechanical problem such as a vacuum leak or a faulty pressure regulator. These types of mechanical problems will cause the 02S to sense a constant lean or constant rich mixture. The mechanical problem will first have to be repaired and then the 02S test repeated.
6. Pull a vacuum hose located after the throttle plate. Voltage should drop to approximately 0.12 volts (while still fluctuating rapidly). This tests the ability of the 02S to detect a lean mixture condition. Reattach the vacuum hose.
7. Richen the mixture using a propane enrichment tool. Voltage should rise to approximately 0.90 volts (while still fluctuating rapidly). This tests the ability of the 02S to detect a rich mixture condition.
8. If the 02S voltage is above or below the specified range, the 02S and/or the O2S wiring may be faulty. Check the wiring for any breaks, repair as necessary and repeat the test.

Heated Oxygen Sensor

1. Start the engine and bring it to normal operating temperature, then run the engine above 1200 rpm for two minutes.
2. Turn the ignition OFF disengage the H02S harness connector.
3. Connect a test light between harness terminals +B and HT. With the ignition switch ON and the engine off, verify that the test light is lit. If the test light is not lit, either the supply voltage to the H02S heater or the ground circuit of the H02S heater is faulty. Check the H02S wiring and the fuse.
4. Next, connect a high impedance ohmmeter between the H02S terminals of the heating element and verify that the resistance is 11.0–16.0 ohms at 68°F (20°C).

   Fig. 1: Using an ohmmeter, measure the resistance between the terminals of the oxygen sensor

5. If the H02S heater resistance is not as specified, the H02S may be faulty.
6. Start the engine and bring it to normal operating temperature, then run the engine above 1200 rpm for two minutes.
7. Backprobe with a high impedance averaging voltmeter (set to the DC voltage scale) between the oxygen sensor (02S) signal wire and battery ground.
8. Verify that the 02S voltage fluctuates rapidly between 0.40–0.60 volts.
9. If the 02S voltage is stabilized at the middle of the specified range (approximately 0.45–0.55 volts) or if the 02S voltage fluctuates very slowly between the specified range (02S signal crosses 0.5 volts less than 5 times in ten seconds), the 02S may be faulty.
10. If the 02S voltage stabilizes at either end of the specified range, the ECM is probably not able to compensate for a mechanical problem such as a vacuum leak or a faulty fuel pressure regulator. These types of mechanical problems will cause the 02S to sense a constant lean or constant rich mixture. The mechanical problem will first have to be repaired and then the 02S test repeated.
11. Pull a vacuum hose located after the throttle plate. Voltage should drop to approximately 0.12 volts (while still fluctuating rapidly). This tests the ability of the 02S to detect a lean mixture condition. Reattach the vacuum hose.
12. Richen the mixture using a propane enrichment tool. Voltage should rise to approximately 0.90 volts (while still fluctuating rapidly). This tests the ability of the 02S to detect a rich mixture condition.
13. If the 02S voltage is above or below the specified range, the 02S and/or the O2S wiring may be faulty. Check the wiring for any breaks, repair as necessary and repeat the test.