Circuit Description
The heated oxygen sensor (HO2S) produces a voltage that varies between -100 mV and 900 mV under normal operating conditions. On the Catera, the full operating range of the HO2S circuit is approximately from -406 mV to 1124 mV. The Engine Control Module (ECM) monitors this voltage and determines if the exhaust is lean or rich. The oxygen sensor voltage is high when the exhaust is rich, and low when the exhaust is lean. The ECM constantly monitors the HO2S signal during the closed loop operation and compensates for a rich or lean condition by decreasing or increasing the injector pulse width as necessary. If the ECM detects an excessively low HO2S voltage, this DTC will set.
Conditions for Running the DTC
| • | No DTCs are set. |
| • | The HO2S heater is on for longer than 200 seconds. |
| • | The secondary AIR diagnostic is not running |
Conditions for Setting the DTC
| • | The HO2S voltage is below -148 mV. |
| • | The above condition met for longer than 0.2 seconds. |
Action Taken When the DTC Sets
The ECM illuminates the malfunction indicator lamp (MIL) and records the operating conditions in the Freeze Frame on the second consecutive drive trip that the diagnostic runs and fails.
Conditions for Clearing the MIL/DTC
| • | The ECM turns OFF the MIL after three consecutive drive trips that the diagnostic runs and passes. |
| • | A History DTC clears after forty consecutive warm-up cycles in which no failures are reported by this diagnostic or any other emission related diagnostic. |
| • | The ECM battery voltage is interrupted. |
| • | The scan tool clears the MIL/DTC. |
Diagnostic Aids
Use the Connector Test Adapter Kit J 35616 for any test that requires probing the ECM harness connector or a component harness connector. Using this kit will prevent damage to the harness connector terminals.
Check for the following conditions:
| • | The sensor pigtail or the harness may be mis-positioned and contacting the exhaust system. |
| • | Heated oxygen sensor wiring. Check for the following conditions: |
| - | Inspect the harness connectors for the following conditions: |
| - | Backed out terminals |
| - | Improper mating |
| - | Broken locks |
| - | Improperly formed or damaged terminals |
| - | Poor terminal to wire connection |
| - | Corrosion and water intrusion |
| - | Refer to Electrical Diagnosis in Engine Electrical, Troubleshooting Procedures for the proper procedure. Also, refer to Checking Terminal Contact in ECM Diagnosis for the proper procedure. An oxygen supply inside of the HO2S is necessary for a proper operation. This supply of oxygen is provided through the HO2S wires. All of the HO2S wires and connections should be inspected for any breaks or any contamination. If any wiring repairs need to be made, refer to Electrical Diagnosis in Engine Electrical, Electrical Diagnosis, Repair Procedures. |
| - | Poor ECM to engine grounds. |
| - | If the above are OK, the HO2S may be at fault. |
Test Description
The number(s) below refer to the step numbers on the diagnostic table.
-
The engine must be at the normal operating temperature before performing this test.
-
Using the Freeze Frame data may aid in locating an intermittent condition. If the DTC cannot be duplicated, review the information in the Freeze Frame. Try to operate the vehicle within the same freeze frame conditions (the RPM, the MAF, the vehicle speed, the temperature etc.) that were noted. This process may help in order to recreate the malfunction.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System check? | -- | ||
Does the HO2S voltage remain below the specified value? | -148 mV | |||
Is this DTC set? | -- | Refer to Diagnostic Aids | ||
4 |
Important: With HO2S connector disconnected, check the HO2S connector for any water intrusion or corrosion. If necessary, refer to step 21. Does the scan tool indicate HO2S voltage within the specified range? | 375-525 mV | ||
5 | Measure the voltage from the HO2S signal circuit in the HO2S harness connector to ground with the DVM J 39200 . Is the voltage within the specified range? | 900-1200 mV | ||
6 | Measure the voltage from the HO2S Low circuit in the HO2S harness connector to ground with the DVM J 39200 . Is the voltage within the specified range? | 700-800 mV | ||
7 |
Does disconnecting one of the other sensors restore the voltage to the specified range? | 700-800 mV | ||
8 |
Is there any voltage present? | -- | ||
9 | Check the harness for continuity of the HO2S Low circuit with the DVM J 39200 . Is continuity indicated? | -- | ||
10 | Check the harness for continuity between the HO2S Low circuit and battery ground with the DVM J 39200 . Is continuity indicated? | -- | ||
11 |
Is there any voltage present? | -- | ||
12 | Check the harness for continuity of the HO2S Signal circuit with the DVM J 39200 . Is continuity indicated? | -- | ||
13 | Check the harness for continuity between the HO2S Signal circuit and battery ground with the DVM J 39200 . Is continuity indicated? | -- | ||
14 | Replace the shorted HO2S. Is the action complete? | -- | -- | |
15 |
Is the action complete? | -- | -- | |
16 | Repair the open/high resistance in the HO2S Low circuit. Is the action complete? | -- | -- | |
17 | Repair the short to ground in the HO2S Low circuit. Is the action complete? | -- | -- | |
18 | Repair the signal circuit that is shorted to voltage. Is the action complete? | -- | -- | |
19 | Repair the open/high resistance in the signal circuit. Is the action complete? | -- | -- | |
20 | Repair the short to ground in the signal circuit. Is the action complete? | -- | -- | |
21 | Check for a poor connection or poor terminal tension at the ECM harness connector. Refer to Electrical Diagnosis in Engine Electrical, and Troubleshooting Procedures for the proper procedure. Also, refer to Checking Terminal Contact in Engine Control Module Diagnosis . Was a problem found and corrected? | -- | ||
22 |
Important: This vehicle is equipped with a Theft Deterrent System which interfaces with the Engine Control Module (ECM). Program the new ECM with the frequency code of the theft deterrent module that is currently on the vehicle. Replace the ECM. Refer to Engine Control Module Replacement/Programming . Is the action complete? | -- | -- | |
23 |
Is this DTC set? | -- | ||
24 | Were there any additional DTCs noted during the Powertrain OBD System Check that have not been diagnosed? | -- | Go to the applicable DTC table | The System is OK |
