Circuit Description
The DTC P0038 Heated Oxygen Sensor (HO2S) Heater Control Circuit High Voltage Sensor 2 diagnostic monitors the operation of the HO2S 2 heater circuit. The heaters in the oxygen sensors increase the amount of time the sensor spends in Closed Loop fuel control operation or catalyst monitoring operation. The oxygen sensor heater is required by the post-catalyst HO2S 2 in order to maintain the high operating temperatures. The heater helps provide accurate oxygen content readings of the engine exhaust by the HO2S.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P0038 Heated Oxygen Sensor (HO2S) Heater Control Circuit High Voltage Sensor 2
Conditions for Running the DTC
| • | The engine is operating. |
| • | The battery is between 10.5-16 volts. |
| • | DTC P0038 runs continuously once the above conditions have been met. |
Conditions for Setting the DTC
| • | The HO2S 2 heater current is more than 2 amps. |
| • | The HO2S 2 heater is commanded OFF. |
| • | The condition exists for more than 0.3 seconds. |
Action Taken When the DTC Sets
| • | The powertrain control module (PCM) illuminates the malfunction indicator lamp (MIL). |
| • | The PCM records the operating conditions at the time the diagnostic fails. This information is stored in the Freeze Frame buffer. |
| • | The PCM will turn OFF the heater in the oxygen sensor. |
Conditions for Clearing the MIL/DTC
| • | The MIL turns OFF after 3 consecutively passing trips without a fault present. |
| • | A History DTC clears after 40 consecutive warm-up cycles without a fault. |
| • | Use the scan tool Clear DTC Information function in order to clear the DTC. |
Diagnostic Aids
Check for any of the following conditions:
| • | If a DTC P0038 is intermittent, driving the vehicle under the conditions outlined in the Inspection/Maintenance (I/M) section for HO2S tests can verify whether the fault is present. |
| • | The HO2S heater diagnostic checks for many of the faults that can cause DTC P0038 to set. If the HO2S heater test passes, the cause of the DTC is probably intermittent. Clear the DTC information. Road test the vehicle while monitoring the HO2S heater test in the I/M System Information selection on the scan tool. When the HO2S heater test indicates complete with a YES status, check for a DTC P0038 under Last Test Failed. If there is no DTC P0038 indicated, the DTC is intermittent and the HO2S heater diagnostic is indicating OK at this time. |
| • | An intermittent malfunction may be caused by a fault in the HO2S 2 sensor electrical circuit. Inspect the wiring harness and components for an intermittent condition. Refer to Intermittent Conditions . |
| • | Repair any electrical circuit faults that were found. Refer to Wiring Repairs . |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
The Diagnostic System Check - Vehicle prompts the technician to complete some basic checks and store the Freeze Frame data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored in the scan tool for later reference.
-
This step checks whether the malfunction that caused the DTC P0038 is still present. Operating the vehicle in check mode enhances the diagnostic capabilities of the PCM. The HO2S Heater diagnostic can be monitored on the scan tool under the I/M System Information selection of System Information. When the HO2S Heater test displays a YES status, indicating that the oxygen sensor heater diagnostic is completed, check for a DTC P0038 in the Last Test Failed screen of the scan tool. If there is no DTC P0038 displayed the HO2S heater diagnostic has run and passed, indicating that no malfunction was present this time. The DTCs MUST be cleared in order to view the Current Status of the system diagnostics being performed. Do not forget that I/M System Information tests only indicate that the test has run, not whether the test passed or failed. The Last Test Failed screen must be checked for related DTCs in order to determine the outcome of the diagnostic test involved. For additional information on check mode operation refer to Powertrain Control Module Diagnosis.
-
This step tests the heater control circuit of the HO2S 2 for a short to voltage. If the test lamp illuminates, this indicates a short to voltage on the heater control circuit.
-
This step isolates the condition. Review the system mechanization. If the test lamp still illuminates after the PCM is disconnected, repair the short to an ignition voltage source. If the test lamp does not illuminate, test for a short between the heater control circuit and any other circuit powered by the PCM that run together inside the same harness.
-
Inspect the HO2S 2 connectors for water intrusion, corrosion, and bent or damaged terminals.
-
Inspect the PCM connectors for water intrusion, corrosion, and bent or damaged terminals.
Step | Action | Value | Yes | No |
|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics Connector End View Reference: Powertrain Control Module Connector End Views or Engine Controls Connector End Views | ||||
Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | ||
Did a DTC P0038 set? | -- | Go to Step 3 | Go to Diagnostic Aids | |
3 |
Is the resistance of the sensor within the specified range? | 11-16 ohms at 20°C (68°F) | Go to Step 4 | Go to Step 10 |
Does the test lamp illuminate? | -- | Go to Step 5 | Go to Step 7 | |
Does the test lamp illuminate? | -- | Go to Step 9 | Go to Step 6 | |
6 | Test for a short to a voltage between heater control circuit of the HO2S 2 and another PCM circuit. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 8 |
Test for shorted terminals and for poor connections at the HO2S 2. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 10 | |
Test for shorted terminals and for poor connections at the PCM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 11 | |
9 | Repair the short to voltage in the heater control circuit of the HO2S 2. Refer to Wiring Repairs . Did you complete the repair? | -- | Go to Step 12 | -- |
10 | Replace the HO2S 2. Refer to Heated Oxygen Sensor 2 Replacement . Did you complete the replacement? | -- | Go to Step 12 | -- |
11 | Replace the PCM. Refer to Control Module References for replacement, setup, and programming. Did you complete the replacement? | -- | Go to Step 12 | -- |
12 |
Does the DTC run and pass? | -- | Go to Step 13 | Go to Step 2 |
13 | Observe the Capture Info with a scan tool. Are there any DTCs that you have not diagnosed? | -- | System OK | |
