Circuit Description
The heated oxygen sensor (HO2S) heater is a device used to reduce the time that the HO2S sensor takes to go active. The HO2S bank 1 sensor 2 heater helps to maintain the sensor at the proper temperature for catalyst testing, and additional adjustments to fuel trim. The HO2S heater receives power through a fused ignition circuit. The powertrain control module (PCM) turns the heater ON, and OFF using a low side driver output driver module (ODM) located within the PCM.
The PCM will test the heater only after a cold start. The PCM determines a cold start based on the difference between the engine coolant temperature (ECT) at the last key OFF, and the ECT at the current key ON. When the HO2S voltage indicates a sufficiently active sensor, the PCM looks at how much time has elapsed since start-up. If the PCM determines that too much time was required for the sensor to become active, this diagnostic trouble code (DTC) will set. The amount of time for the sensor to reach operating temperature is based on the ECT at start-up and the average mass air flow (MAF) since start-up. More airflow and/or higher start-up ECT results in a shorter time to sensor activity).
Conditions for Running the DTC
| • | DTCs P0137, P0138, and P0140 are not set |
| • | The difference between ECT at last key OFF and the current key ON indicates a cold start. |
| • | The system voltage is between 10-18 volts. |
| • | The average MAF is less than 30 g/s. |
Conditions for Setting the DTC
The HO2S bank 1 sensor 2 voltage remains within 150 mV of the bias voltage, approximately 450 mV, for a longer amount of time than expected. The amount of time for the sensor to reach operating temperature is based on the ECT at start-up, and the average mass air flow since start-up for a maximum time of 200 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. |
Diagnostic Aids
If the condition is intermittent, refer to Intermittent Conditions .
Step | Action | Value(s) | Yes | No | ||||||
|---|---|---|---|---|---|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics | ||||||||||
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | |||||||
2 |
Does DTC P0036 set? | -- | Go to DTC P0036 | Go to Step 3 | ||||||
3 |
Does the scan tool indicate the HO2S voltage varying outside the specified range? | 400-500 mV | Go to Step 4 | Go to Step 5 | ||||||
4 |
Does the scan tool indicate this DTC passed? | -- | Go to Intermittent Conditions | Go to Step 5 | ||||||
5 |
Does the scan tool indicate the HO2S bank 1 sensor 2 voltage is below the specified value? | 150 mV | Go to Step 9 | Go to Step 6 | ||||||
6 | Connect a jumper wire between the HO2S bank 1 sensor 2 high signal circuit and a good ground. Does the scan tool indicate the HO2S bank 1 sensor 2 voltage is below the specified value? | 150 mV | Go to Step 8 | Go to Step 7 | ||||||
7 |
Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 10 | ||||||
8 |
Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 10 | ||||||
9 | Inspect for poor connections at the harness connector of the HO2S bank 1 sensor 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 13 | Go to Step 11 | ||||||
10 | Inspect for poor connections 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 13 | Go to Step 12 | ||||||
11 |
Notice: Contamination of the oxygen sensor can result from the use of an inappropriate RTV sealant (not oxygen sensor safe) or excessive engine coolant or oil consumption. Remove the HO2S and visually inspect the portion of the sensor exposed to the exhaust stream in order to check for contamination. If contaminated, the portion of the sensor exposed to the exhaust stream will have a white powdery coating. Silicon contamination causes a high but false HO2S signal voltage (rich exhaust indication). The control module will then reduce the amount of fuel delivered to the engine, causing a severe driveability problem. Eliminate the source of contamination before replacing the oxygen sensor. Important: Determine the cause of the contamination before replacing the sensor.
Did you complete the replacement? | -- | Go to Step 13 | -- | ||||||
12 | Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | -- | Go to Step 13 | -- | ||||||
13 |
Does the DTC run and pass? | -- | Go to Step 14 | Go to Step 2 | ||||||
14 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | -- | System OK | |||||||
