Circuit Description
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. With the engine running, ground is provided to the heater by the HO2S heater low control circuit, through a low side driver within the engine control module (ECM).
The ECM commands the heater ON or OFF to maintain a specific HO2S operating temperature range. The ECM monitors the voltage on the HO2S heater low control circuit for heater fault diagnosis. If the ECM detects that the HO2S heater low control circuit voltage is not within a specified range, DTC P0030 sets for HO2S bank 1 sensor 1, DTC P0036 sets for HO2S bank 1 sensor 2, DTC P0050 sets for HO2S bank 2 sensor 1, or DTC P0056 sets for HO2S bank 2 sensor 2.
DTC Descriptors
This diagnostic procedure supports the following DTCs:
| • | DTC P0030 HO2S Heater Control Circuit Bank 1 Sensor 1 |
| • | DTC P0036 HO2S Heater Control Circuit Bank 1 Sensor 2 |
| • | DTC P0050 HO2S Heater Control Circuit Bank 2 Sensor 1 |
| • | DTC P0056 HO2S Heater Control Circuit Bank 2 Sensor 2 |
Conditions for Running the DTC
| • | The Ignition 1 Signal parameter is between 10-18 volts. |
| • | This diagnostic runs continuously when the above condition is met. |
Conditions for Setting the DTC
The ECM detects that the affected HO2S heater low control circuit is not within a specified range for 6 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.
Step | Action | Value(s) | Yes | No | ||||
|---|---|---|---|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics Connector End View Reference: Powertrain Control Module Connector End Views or Engine Controls Connector End Views | ||||||||
1 | Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | |||||
2 |
Important: Whenever the heated oxygen sensor (HO2S) heaters are commanded ON with a scan tool, they will continue to be pulsed ON once per second until the ignition is turned OFF for 30 seconds.
Is the HO2S Heater Current parameter within the specified range? | 0.25-1.375 A | Go to Step 3 | Go to Step 4 | ||||
3 |
Did the DTC fail this ignition? | -- | Go to Step 4 | Go to Testing for Intermittent Conditions and Poor Connections | ||||
4 | Inspect the O2A or O2B fuse. Is the O2A or O2B fuse open? | -- | Go to Step 5 | Go to Step 6 | ||||
5 | Test the ignition 1 voltage circuit for a short to ground. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 20 | Go to Step 8 | ||||
6 |
Does the test lamp illuminate? | -- | Go to Step 7 | Go to Step 17 | ||||
|
Important: The test lamp may blink prior to commanding the heaters ON. This is because the heaters were commanded ON in a previous step. To command the heaters OFF, turn OFF the ignition for 30 seconds.
Does the test lamp blink once per second? | -- | Go to Step 9 | Go to Step 10 | |||||
8 |
Important: Perform the following test on all HO2S which are supplied voltage by the suspect circuit. Test the ignition 1 voltage circuit on the sensor side of the HO2S connector for a short to ground. Refer to Circuit Testing . Is any sensor shorted to ground? | -- | Go to Step 18 | Go to Testing for Intermittent Conditions and Poor Connections | ||||
9 | Measure the resistance of the following circuits with a DMM:
Refer to Circuit Testing . Is the resistance of either circuit more than the specified value? | 3 ohms | Go to Step 16 | Go to Step 14 | ||||
10 | Is the test lamp on steady? | -- | Go to Step 11 | Go to Step 12 | ||||
11 | Test the HO2S heater low control circuit for a short to ground. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 20 | Go to Step 15 | ||||
12 | Test the HO2S heater low control circuit for a short to voltage. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 20 | Go to Step 13 | ||||
13 | Test the HO2S heater low control circuit for an open or high resistance. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 20 | Go to Step 15 | ||||
14 | Test for shorted terminals and for poor connections at the HO2S. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | -- | Go to Step 20 | Go to Step 18 | ||||
15 | Test for shorted terminals and for poor connections at the powertrain control module (PCM). Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | -- | Go to Step 20 | Go to Step 19 | ||||
16 | Repair the circuit with high resistance. Refer to Wiring Repairs . Did you complete the repair? | -- | Go to Step 20 | -- | ||||
17 | Repair the open or high resistance in the ignition 1 voltage circuit. Refer to Wiring Repairs . Did you complete the repair? | -- | Go to Step 20 | -- | ||||
18 | Replace the affected HO2S. Refer to the following: Did you complete the replacement? | -- | Go to Step 20 | -- | ||||
19 | Replace the PCM. Refer to Control Module References for replacement, setup, and programming. Did you complete the replacement? | -- | Go to Step 20 | -- | ||||
20 |
Did the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 21 | ||||
21 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | System OK | |||||
