Circuit Description
In order to control emissions, a 3-way catalytic converter (TWC) 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 TWC, 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.
Replace the entire HO2S 2 assembly. DO NOT attempt to repair the HO2S 2 if the following conditions exist:
| • | Damaged wiring |
| • | Damaged electrical connectors |
| • | Damaged terminals |
Obstruction of the air reference and degraded HO2S 2 performance could result from any attempt to repair the above conditions.
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.
Conditions for Running the DTC
| • | DTCs P0105, P0107, P0108, P0112, P0113, P0117, P0118, P0122, P0123, P0171, P0172, P0201-P0204, P0300, P0301-P0304, P0336, P0440, P0446, P0452, P0453, P0506, P0507, P0601, P0602, or P1441 are not set. |
| • | The engine is in deceleration fuel cut-off (DFCO) mode. |
| • | The battery voltage is more than 10 volts. |
| • | The engine coolant temperature (ECT) is more than 75°C (167°F). |
| • | The fuel level is more than 10 percent. |
| • | The engine has been running more than 10 seconds. |
Conditions For Setting The DTC
The HO2S 2 remains more than 648 mV for more than 10 seconds. The diagnostic then will run for 11 seconds after a 10 second delay 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 1,000 millivolts. Disconnect the HO2S 2 and connecting a jumper wire between the HO2S 2 low circuit to engine ground. Replace the HO2S 2 if the displayed voltage goes from more than 1000 mV to approximately 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:
| • | A poor electrical connection |
| • | Rubbed-through wire insulation |
| • | A broken wire inside of the insulation |
Replace the entire HO2S 2 assembly. DO NOT attempt to repair the HO2S 2 if the following conditions exist:
| • | Damaged wiring |
| • | Damaged electrical connectors |
| • | Damaged terminals |
Obstruction of the air reference and degraded HO2S 2 performance could result from any attempt to repair the above conditions.
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 diagnostic trouble code (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 below 100 mV. If the signal voltage is still high, the this indicates that 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 DTC codes set? | -- | Go to Step 3 | |||||
Check the HO2S 2 voltage with the scan tool. Does the HO2S 2 sensor voltage measure above the specified value? | 1,042 mV | Go to Step 5 | Go to Step 4 | |||||
4 |
Is the HO2S 2 voltage above the specified value? | 1,042 mV | Go to Step 5 | Go to Step 10 | ||||
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 of the specified value? | 0 V | Go to Step 6 | Go to Step 7 | ||||
Does the scan tool indicate the HO2S 2 voltage below the specified value? | 100 mV | Go to Step 8 | Go to Step 9 | |||||
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 10 | -- | ||||
8 |
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 10 | -- | ||||
9 |
Did you complete the replacement? | -- | Go to Step 10 | -- | ||||
10 |
Does the DTC run and pass? | -- | Go to Step 11 | Go to Step 2 | ||||
11 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | -- | System OK | |||||
