Circuit Description
Heating elements inside the heated oxygen sensors (HO2S) minimize the time required for the sensors to reach operating temperature, and to provide an accurate voltage signal, the HO2S heater operation is controlled by the powertrain control module (PCM). The HO2S 2 is supplied power from the external ignition 1 voltage circuit. The PCM controls the HO2S 2 heater low control circuit with a low side driver. The HO2S 2 heater diagnostic monitors the current draw through the low side driver when the engine is running. The HO2S 2 heater diagnostic will run only after a cold start. To determine if the engine has been started from cold the PCM compares the engine coolant temperature (ECT) at key ON to that at the last key OFF. The ECT difference and the average mass air flow (MAF) since start-up determines how much time that the HO2S 2 should take to produce an active voltage signal. If the PCM detects an HO2S 2 voltage signal with a slower than expected time to activity, P0141 will set.
Conditions for Running the DTC
| • | DTCs P0137, P0138, P0140 are not set. |
| • | The PCM has determined the current ignition cycle is a cold start. |
| • | The system voltage is between 10-18 volts. |
| • | The average MAF is less than 30 grams per second. |
| • | The HO2S Bank 1 Sensor 2 voltage parameter is between 360-540 mV at start-up. |
Conditions for Setting the DTC
The PCM detects that the HO2S 2 voltage remains within 150 mV of the bias voltage for a longer amount of time than expected.
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-Engine Controls? | -- | Go to Step 2 | |
2 |
Did DTC P0036 fail this ignition? | -- | Go to DTC P0036 | Go to Step 3 |
|
Important:: If the engine has just been operating, allow engine to cool until the heated oxygen sensor (HO2S) 2 voltage is stable, or near the bias voltage before proceeding.
Does the HO2S 2 voltage go above or below the previously stabilized voltage by at least as much as the specified value within 2 minutes? | 100 mV | Go to Step 4 | Go to Step 5 | |
4 |
Did the DTC fail this ignition? | -- | Go to Intermittent Conditions | Go to Step 5 |
5 |
Important: The test lamp must be connected to a good ground.
Does the test lamp illuminate? | -- | Go to Step 6 | Go to Step 6 |
6 |
Does the test lamp illuminate? | -- | Go to Step 7 | Go to Step 8 |
7 |
Important: The heater element resistance will vary according to HO2S temperature. A hot HO2S heater element will have a higher resistance than a heater element at room temperature.
Is the resistance within the specified value? | 2-20 ohms | Go to Step 13 | Go to Step 10 |
8 | Test the HO2S 2 low control circuit for an open or high resistance. 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 an intermittent and for a poor connection at the harness connector of the HO2S 2. 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 an intermittent and for a poor connection at the harness connector of the PCM. 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 | Repair the open in the HO2S 2 heater ignition 1 voltage circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 14 | -- |
12 | Replace the HO2S 2. Refer to Heated Oxygen Sensor Replacement - Bank 1 Sensor 2 . Did you complete the replacement? | -- | Go to Step 14 | -- |
13 | Replace the PCM. Refer to Powertrain 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 | |
