Circuit Description
The heated oxygen sensors (HO2S) are used for fuel control and post catalyst monitoring. Each HO2S compares the oxygen content of the surrounding air with the oxygen content in the exhaust stream. The HO2S must reach operating temperature to provide an accurate voltage signal. A heating element inside the HO2S minimizes the time required for the sensor to reach operating temperature. Voltage is provided to the heater by the ignition 1 voltage circuit through a fuse. Ground is provided to the heater on the control circuit by a low side driver within the control module. The control module monitors the control circuit of the heater to determine if a failure is present.
If the ECM detects an open or short to ground on the control circuit of the H02S heater, a DTC sets.
DTC Descriptor
This diagnostic procedure supports the following DTCs:
| • | DTC P0031 HO2S Heater Control Circuit Low Voltage Bank 1 Sensor 1 |
| • | DTC P0037 HO2S Heater Control Circuit Low Voltage Bank 1 Sensor 2 |
| • | DTC P0051 HO2S Heater Control Circuit Low Voltage Bank 2 Sensor 1 |
| • | DTC P0057 HO2S Heater Control Circuit Low Voltage Bank 2 Sensor 2 |
Conditions for Running the DTC
| • | The engine is operating. |
| • | The DTCs run continuously once the above condition is met. |
Conditions for Setting the DTC
The ECM detects an open or short to ground on the control circuit of the H02S heater for more than 25 seconds.
Action Taken When the DTC Sets
| • | The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails. |
| • | The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records. |
Conditions for Clearing the MIL/DTC
| • | The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail. |
| • | A current DTC, Last Test Failed, clears when the diagnostic runs and passes. |
| • | A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic. |
| • | Clear the MIL and the DTC with a scan tool. |
Test Description
The number below refers to the step number on the diagnostic table.
-
This step is testing the heater control circuit for a short to ground.
-
This step is testing the heater control circuit for an open.
Step | Action | Values | Yes | No | ||||
|---|---|---|---|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics Connector End View Reference: Engine Control Module Connector End Views or Engine Controls Connector End Views | ||||||||
1 | Did you perform the Diagnostic System Check - Engine Controls? | -- | Go to Step 2 | |||||
2 |
Important: It may take up to 8 minutes for this DTC to set. Did DTC P0031, P0037, P0051, or P0057 fail this ignition? | -- | Go to Step 4 | Go to Step 3 | ||||
3 |
Did the DTC fail this ignition? | -- | Go to Step 4 | Go to Intermittent Conditions | ||||
4 |
Does the test lamp illuminate? | -- | Go to Step 5 | Go to Step 11 | ||||
Does the test lamp illuminate? | -- | Go to Step 7 | Go to Step 6 | |||||
Does the test lamp illuminate? | -- | Go to Step 7 | Go to Step 8 | |||||
7 | Measure the voltage between the heater control circuit of the HO2S and a good ground with a DMM. Is the voltage within the specified range? | 3.0-4.0 V | Go to Step 9 | Go to Step 10 | ||||
8 | Test the control circuit of the HO2S heater for one of the following conditions:
Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 14 | Go to Step 10 | ||||
9 | Test for shorted terminals and poor connections at the HO2S. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 14 | Go to Step 12 | ||||
10 | Test for shorted terminals and poor connections at the ECM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 14 | Go to Step 13 | ||||
11 |
Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 14 | -- | ||||
12 | Replace the appropriate HO2S. Did you complete the replacement? | -- | Go to Step 14 | -- | ||||
13 | Replace the engine control module (ECM). Refer to Engine Control Module Replacement . Did you complete the replacement? | -- | Go to Step 14 | -- | ||||
14 |
Did the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 15 | ||||
15 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | System OK | |||||
