Circuit Description
The powertrain control module (PCM) has the ability to monitor this process by using a rear heated oxygen sensor (HO2S 2). The rear HO2S 2, located in the exhaust stream past the catalytic converter, produces an output signal relative to the oxygen storage capacity of the catalytic converter. The PCM then calculates the ability of the catalytic converter to convert the exhaust emissions effectively. Whenever the catalytic converter is functioning properly, the rear HO2S 2 signal will be far less active than the signal produced by the front oxygen sensor 1 (O2S 1).
Conditions for Running the DTC
| • | No active MAP DTCs |
| • | No active IAT DTCs |
| • | No active ECT DTCs |
| • | No active TP DTCs |
| • | No active fuel trim DTCs |
| • | No active injector control DTCs |
| • | No active misfire DTCs |
| • | No active CKP DTCs |
| • | No active EVAP DTCs |
| • | No active IAC DTCs |
| • | No active PCM memory DTCs |
| • | Air flow is more than 5.5 grams per second |
| • | Engine coolant temperature (ECT) is more than 40°C (104°F) |
| • | The above conditions are met for 140 seconds |
| • | Throttle position (TP) angle is between 5 percent and 50 percent for 4 seconds |
Conditions For Setting The DTC
HO2S 2 voltage is more than 1042 mV for 125 seconds.
Action Taken When the DTC Sets
| • | The control module illuminates the malfunction indicator lamp (MIL) if a failure is detected during 2 consecutive key cycles. |
| • | The control module sets the DTC and records the operating conditions at the time the diagnostic failed. The failure information is stored in the scan tools Freeze Frame and Failure Records. |
Conditions for Clearing the MIL/DTC
| • | The control module turns OFF the MIL after 3 consecutive drive trips when the test has Run and Passed |
| • | A history DTC will clear if no fault conditions have been detected for 40 warm-up cycles. A warm up cycle occurs when the coolant temperature has risen 22°C (40°F) from the startup coolant temperature and the engine coolant reaches a temperature that is more than 70°C (158°F) during the same ignition cycle. |
| • | Use a scan tool to clear the DTCs. |
Diagnostic Aids
Whenever the oxygen sensor pigtail wiring, connector, or terminal are damaged, the entire oxygen sensor assembly must be replaced. Do not attempt to repair the wiring, connector, or terminals. In order for the sensor to function properly, the O2S must have a clean air reference. This clean air reference is obtained by way of the oxygen sensor wires. Any attempt to repair the wires, connectors, or terminals may result in the obstruction of the air reference and degrade the performance of the oxygen sensor.
Check for the following conditions:
| • | A rich exhaust -- An overly rich exhaust may load the catalytic converter causing high rear HO2S 2 signal voltages. |
| • | A silicone contamination -- A silicone contamination of the rear HO2S 2 may cause a false rich condition. A powdery white deposit on the rear HO2S 2 will indicate this condition. |
| • | A faulty HO2S 2 -- Whenever the rear HO2S 2 is internally shorted, the rear HO2S 2 voltage displayed on a scan tool will be over 1.0 volt. Disconnect the rear HO2S 2 . Jumper the rear HO2S low circuit to the engine ground. Whenever the rear HO2S 2 voltage goes from 100 mV to around 450 mV, replace the rear HO2S 2. |
| • | An intermittent test -- Observe the rear HO2S 2 on a scan tool while moving the related connectors and wiring harness with the key ON. Whenever the fault is induced, the rear HO2S 2 display will change. This may help isolate the location of the malfunction. |
| • | A damaged harness -- Inspect the PCM harness for a short to voltage in the rear HO2S 2 low circuit. |
Test Description
The numbers below refer to the step number on the diagnostic table:
-
This step determines if DTC P0138 is the result of a hard malfunction or an intermittent condition.
-
Disconnecting the HO2S 2 and connecting a jumper wire between the HO2S 2 signal circuit and the HO2S 2 low circuit to ground should cause the scan tool to display an HO2S 2 voltage below 100 mV . If the signal voltage is still high, the this indicates that the PCM is malfunctioning.
-
The replacement PCM must be programmed and the Crankshaft Position System Variation Learn procedure must be performed.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | ||
2 | With the scan tool, observe the HO2S 2 voltage. Does the HO2S 2 voltage read more than the specified value? | 1,042 mV | ||
Does the HO2S 2 voltage read more than the specified value? | 1,042 mV | Go to Diagnostic Aids | ||
4 |
Caution: Avoid contact with moving parts and hot surfaces while working around a running engine in order to prevent physical injury. Does the HO2S 2 signal voltage read at the specified value? | 0 V | ||
Does the HO2S 2 voltage read less than the specified value? | 100 mV | |||
6 | Repair the short to voltage in the HO2S 2 sensor signal circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | -- | |
7 |
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 sensor. Refer to Heated Oxygen Sensor Replacement . Did you complete the replacement? | -- | -- | |
|
Important:: The replacement PCM must be programmed. Replace the PCM. Refer to Powertrain Control Module Replacement/Programming . Did you complete the replacement? | -- | -- | ||
9 |
Does the DTC reset? | -- | System OK |
