Circuit Description
In order to control emissions, a 3-way catalytic converter converts any harmful exhaust emissions into harmless water vapor and carbon dioxide.
The powertrain control module (PCM) has the capability to monitor this process by using a rear heated oxygen sensor (HO2S 2). The HO2S 2 , located in the exhaust stream past the catalytic converter, produces an output signal which indicates the storage capacity of the catalyst. This in turn indicates the catalysts ability to convert the exhaust emissions effectively. If the catalyst is functioning properly, the HO2S 2 signal will be far less active than the signal produced by the front oxygen sensor (O2S 1).
Conditions for Running the DTC
| • | DTCs P0105, P0107, P0108, P0112, P0113, P0117, P0118, P0122, P0123, P0171, DTC P0172, P0201, P0202, P0203, P0204, P0300, P0301, P0302, P0303, P0304, P0336, P0440, P0446, P0452, P0453, P0506, P0507, P0601, P0602, or P1441 are not set. |
| • | The engine is in decel fuel cut-off (DFCO) mode. |
| • | The battery voltage is greater than 10.0 volts. |
| • | The engine coolant temperature (ECT) is greater than 70°C (158°F). |
| • | The fuel level is greater than 10 percent. |
| • | The engine has been running more than 10 seconds. |
Conditions for Setting the DTC
The HO2S 2 remains greater than 648 mV for more than 10 seconds. The diagnostic then will run for 11 seconds after a 10 second delay in order to complete 1 test.
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
Check for the following conditions:
| • | A rich exhaust--An overly rich exhaust may load the catalyst causing high HO2S 2 signal voltages. |
| • | Silicone contamination--Silicone contamination of HO2S 2 could cause a false rich condition. A powdery white deposit on the sensor will indicate this condition. |
| • | A malfunctioning HO2S 2--If there is an internal short in the HO2S 2, the HO2S 2 voltage displayed on a scan tool will be more than 1 volt. Disconnect the HO2S 2, and connect a jumper wire between the HO2S 2 low signal circuit to engine ground. Replace the HO2S 2 if the displayed voltage goes from over 1,000 mV to around 450 mV . |
| • | An intermittent test--Observe the HO2S 2 on the scan tool while moving the related electrical connectors and the wiring harness with the ignition switch turned ON. If the malfunction is induced, the HO2S 2 display will change. This should help isolate the location of the malfunction. |
| • | Damaged harness--Inspect PCM harness for a short to voltage in the HO2S 2 high signal circuit. |
An intermittent could be the result of the following conditions:
| • | Poor electrical connection |
| • | Rubbed through wire insulation |
| • | Broken wire inside of the insulation |
Obstruction of the air reference and degraded HO2S 2 performance could result in any attempt to repair the HO2S harness or connector.
The HO2S 2 must have a clean air reference in order for the HO2S 2 to function properly. This clean air reference is obtained by way of the HO2S 2 wires.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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This step determines if DTC P1138 is the result of a hard malfunction or an intermittent condition.
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Disconnecting the HO2S 2 and connecting a jumper wire between the HO2S 2 high signal circuit and the HO2S 2 low signal circuit to ground should cause the scan tool to display HO2S 2 voltage less than 100 mV (0.1 volts). If the signal voltage is still high, the PCM is malfunctioning.
Step | Action | Values | Yes | No | ||||
|---|---|---|---|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics | ||||||||
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | |||||
2 | Are any other DTC codes set? | -- | Go to Step 3 | |||||
With the scan tool, observe the HO2S 2 voltage. Is the HO2S 2 voltage more than the specified value? | 1,042 mV | Go to Step 5 | Go to Step 4 | |||||
4 |
Is the HO2S 2 voltage more than the specified value? | 1042 mV | Go to Step 5 | Go to Step 11 | ||||
5 |
Caution: Avoid contact with moving parts and hot surfaces while working around a running engine in order to prevent physical injury. Does the DMM indicate a voltage near the specified value? | 0 V | Go to Step 6 | Go to Step 7 | ||||
Does the scan tool indicate that the HO2S 2 sensor voltage is below the specified value? | 100 mV | Go to Step 8 | Go to Step 10 | |||||
7 | Repair the short to voltage in the HO2S 2 high signal circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 11 | -- | ||||
8 | Inspect for poor connections at the harness connector of the HO2S sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Heated Oxygen Sensor Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 11 | Go to Step 9 | ||||
9 |
Caution: Avoid contact with moving parts and hot surfaces while working around a running engine in order to prevent physical injury. Replace the HO2S 2. Refer to Heated Oxygen Sensor Replacement . Did you complete the replacement? | -- | Go to Step 11 | -- | ||||
10 |
Did you complete the replacement? | -- | Go to Step 11 | -- | ||||
11 |
Does the DTC run and pass? | -- | Go to Step 12 | Go to Step 2 | ||||
12 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | -- | System OK | |||||
