P1138

Diagnostic Chart:

Schematic:

CIRCUIT DESCRIPTION
In order to control emissions, a 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 catalyst's 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 connector
^ Damaged terminals

Obstruction of the air reference and degraded HO2S 2 performance could result in 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, P0202, P0203, P0204, P0300, P0336, P0440, P0446, P0452, P0453, P0506, P0507, P0601, P0602, or P1441 not set.
^ The engine is in DEFCO mode.
^ The battery voltage is more than 10.0 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 for more than 10 seconds.

CONDITIONS FOR SETTING THE DTC
The HO2S 2 remains at more 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 one test.

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 malfunction present.
^ The PCM will record the operating conditions at the time that the diagnostic fails. This information will store in the Freeze Frame and Failure Records buffers.
^ A history DTC stores.

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.
^ Use a scan tool to clear the DTCs.

DIAGNOSTIC AIDS
Check for the following conditions:
^ A rich exhaust - An overly rich exhaust may load the catalyst and cause 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 that is displayed on a scan tool will be more than 1.0 volt. Disconnect the HO2S 2 and connect a jumper wire between the HO2S 2 low circuit to the 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 turned ON. If the malfunction is induced, the HO2S 2 display will change. This should help to isolate the location of the malfunction.
^ Damaged harness - Inspect the PCM harness for a short to voltage in the HO2S 2 signal circuit.

An intermittent could be the result of the following conditions:
^ A faulty electrical connection
^ Rubbed through wire insulation
^ A broken wire inside the insulation

Obstruction of the air reference and degradde HO2S 2 performance could result from any attempt to repair the HO2S harness or connector.

The HO2S 2 must have a clean air reference in order 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.
3. This step determines if DTC P1138 is the result of a hard malfunction or an intermittent condition.
6. 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 HO2S 2 voltage less than 100 mV (0.1 Volts). If the signal voltage is still high, the this indicates that the PCM is malfunctioning.
9. The replacement PCM must be programmed and the Crankshaft Position System Variation Learn procedure must be performed.