P0138

Diagnostic Chart:

Wiring Diagram:

CIRCUIT DESCRIPTION

In order to control emissions, a catalytic converter is used to convert harmful exhaust emissions into harness water vapor and carbon dioxide.

The 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 catalyst's ability to convert 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).

If 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, it must have a clean air reference provided to it. This clean air reference is obtained by way of the oxygen sensor wire(s). Any attempt to repair the wires, connectors or terminals could result in the obstruction of the air reference and degrade oxygen sensor performance.

CONDITIONS FOR SETTING THE DTC

^ DTCs P0106, P0107, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0200, P0300, P0301, P0302, P0303, P0304, P0506, P0507, P1406, P1441 not set.

^ Engine run time is greater than 25 seconds.

^ Engine Coolant Temperature (ECT) is greater than 40°C (104°F).

^ Air/fuel ratio is between 14.5:1 and 14.7:1.

^ Throttle Position (TP) angle is between 8 % and 50 % (manual trans.).

Or

^ Throttle Position (TP) angle is between 5 % and 50 % (auto trans.).

^ Engine has met the above conditions for 140 seconds.

^ O2S 1 voltage is greater than 1042 mV for 50 to 75 seconds.

ACTION TAKEN WHEN THE DTC SETS

^ The Malfunction Indicator Lamp (MIL) will illuminate after two consecutive ignition cycles in which the diagnostic runs with the fault active.

^ The PCM will record operating conditions at the time the diagnostic fails. This information will be stored in the Freeze Frame and Failure Records buffers.

^ A history DTC is stored.

^ Coolant fan turns ON.

CONDITIONS FOR CLEARING THE MIL/DTC

^ The MIL will turn OFF after three consecutive ignition cycles in which the diagnostic runs without a fault.

^ A history DTC will clear after 40 consecutive warm up cycles without a fault.

^ DTC(s) can be cleared by using the scan tool.

DIAGNOSTIC AIDS

Check for the following conditions:

^ Rich exhaust - An overly rich exhaust may load the catalyst causing high HO2S 2 signal voltages.

^ Silicone contamination - A false rich condition may be caused by silicone contamination of HO2S 2. This will be indicated by a powdery white deposit on the sensor.

^ Faulty HO2S 2 - If HO2S 2 is internally shorted, the HO2S 2 voltage displayed on a scan tool will be over 1 volt. Disconnect the HO2S 2 and jumpering CKT 1669 to engine ground; if the displayed voltage goes from over 1000 mV to around 450 mV, replace the HO2S 2.

^ Intermittent test - Observe HO2S 2 on Tech 1 while moving related connectors and wiring harness with the key ON. If the failure is induced, the HO2S 2 display will change. This may help isolate the location of the malfunction.

^ Damaged harness - Inspect PCM harness for a short to voltage in CKT 1668.

TEST DESCRIPTION

Number(s) below refer to the step number(s) on the Diagnostic Table.

1. The Powertrain OBD System Check prompts the technician to complete some basic checks and store the freeze frame and failure records data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored on the scan tool for later reference.

2. This step determines if DTC P0138 is the result of a hard failure or an intermittent condition.

5. Disconnecting HO2S 2 and jumpering CKT's 1668 and 1669 to ground should cause the scan tool to display HO2S 2 voltage below 100 mV (0.1V). If the signal voltage is still high, the PCM is faulty.

8. Replacement PCM's must be reprogrammed. Refer to the latest Techline information for programming procedures.