Circuit Description
Heating elements inside the heated oxygen sensor (HO2S) minimize the time required for the sensors to reach operating temperature and provide an accurate voltage signal. A low side driver within the engine control module (ECM) is pulse width controlled to provide variable current to the heater elements. During warm-up the ECM will reduce the ON time to prevent thermal shock to the sensor components from moisture in the exhaust system. The ECM will not allow full HO2S heating until calibrated limits of time, temperature, and intake airflow have been reached. The ECM periodically monitors the HO2S heater operating state by briefly turning OFF the heater low side driver at regular intervals. A small reference voltage is present at the heater low control circuit. When the low side driver is commanded ON, the reference voltage is low, 1.6-3.6 volts. When the low side driver is commanded OFF, the reference voltage is high, close to battery voltage. If the ECM detects that the HO2S heater low control circuit voltage is above 3.6 volts when the heater is commanded ON, DTC P0038 will set for bank 1 sensor 2 or DTC P0058 will set for bank 2 sensor 2.
DTC Descriptors
This diagnostic procedure supports the following DTCs:
| • | P0038 HO2S Heater Control Circuit High Voltage Bank 1 Sensor 2 |
| • | P0058 HO2S Heater Control Circuit High Voltage Bank 2 Sensor 2 |
Conditions for Running the DTC
| • | The Engine Speed parameter is more than 40 RPM. |
| • | The Battery Voltage parameter is between 10.5-17.3 volts. |
| • | DTCs P0038 and P0058 run continuously once the above conditions are met. |
Conditions for Setting the DTC
The ECM detects that the HO2S heater low control circuit voltage is above 3.6 volts for more than 0.5 seconds when the heater is commanded ON, indicating a HO2S heater circuit is shorted to voltage.
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. |
Step | Action | Yes | No |
|---|---|---|---|
Schematic Reference: Engine Controls Schematics Connector End View Reference: Engine Controls Connector End Views or Engine Control Module Connector End Views | |||
1 | Did you perform the Diagnostic System Check - Vehicle? | Go to Step 2 | Go to Diagnostic System Check - Vehicle in Vehicle DTC Information |
2 |
Does the DTC 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 |
Important: Use a known good ground. Do not use the heated oxygen sensor (HO2S) heater low control circuit or HO2S low signal circuit.
Does the test lamp illuminate? | Go to Step 5 | Go to Step 9 |
5 |
Does the test lamp flash ON and OFF? | Go to Step 7 | Go to Step 6 |
6 |
Important: The normal open circuit voltage on the heater low control circuit is 3.5-3.8 volts. Test the affected HO2S heater low control circuit for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 12 | Go to Step 8 |
7 | Test for poor connections and shorted terminals at the harness connector of 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 12 | Go to Step 10 |
8 | Test for poor connections and shorted terminals at the harness connector of the engine control module (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 12 | Go to Step 11 |
9 | Repair the open or high resistance of the affected HO2S heater ignition 1 voltage circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you complete the repair? | Go to Step 12 | -- |
10 | Replace the affected HO2S. Refer to Heated Oxygen Sensor Replacement - Bank 1 Sensor 2 and Heated Oxygen Sensor Replacement - Bank 2 Sensor 2 . Did you complete the replacement? | Go to Step 12 | -- |
11 | Replace the ECM. Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming. Did you complete the replacement? | Go to Step 12 | -- |
12 |
Did the DTC fail this ignition? | Go to Step 2 | Go to Step 13 |
13 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | Go to Diagnostic Trouble Code (DTC) List - Vehicle in Vehicle DTC Information | System OK |
