P1138
CIRCUIT DESCRIPTIONIn 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 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, P0202, P0203, P0204, P0300, P0301, P0302, P0303, P0304, P0336, P0440, P0446, P0452, P0453, P0506, P0507, P0601, P0602, or P1441 are not set.
^ Engine is in DEFCO mode.
^ Battery voltage is more than 10.0 volts.
^ Engine Coolant Temperature (ECT) is more than 75°C (167°F).
^ Fuel level is more than 10 percent.
^ 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 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.
^ The MIL/DTCs can be cleared by using the 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 1.0 volt. 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 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.
Diagnostic Chart (Part 1 Of 2) DTC P1138 HO2S Circuit High Voltage During Decel Fuel Cutoff Sensor 2:
Diagnostic Chart (Part 2 Of 2):
TEST DESCRIPTION
The numbers below refer to the step numbers on the diagnostic table.
1. The Powertrain On-Board Diagnostic (OBD) System Check prompts you to complete some of the basic checks and to store the Freeze Frame and Failure Records data on the scan tool if applicable. This creates an electronic copy of the data captured when the malfunction occurred. The scan tool stores this data for later reference.
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 below 100 mV (0.1 volts). If the signal voltage is still high, the this indicates that the PCM is malfunctioning.
9. Reprogram the replacement PCM. Refer to the latest Techline information for PCM programming.