P0138

CIRCUIT DESCRIPTION
The rear Heated Oxygen Sensor (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 Powertrain Control Module (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
^ DTCs P0105, P0107, P0108, P0112, P0113,P0117, P0118, P0122, P0123, P0169, P0171, P0172, P0178, P0179, P0201, P0202, P0203, P0204, P0300, P0336, P0440, P0446, P0452, P0453, P0506, P0507, P0601, P0602 or P1441 are not set.
^ The Engine Coolant Temperature (ECT) is more than 70°C.
^ Engine run time is more than 10 seconds.
^ The Throttle Position (TP) angle is between 8 percent and 50 percent.
^ Above conditions are met for 3.8 seconds.
^ Closed Loop operation.
^ System voltage is more than 11.7 volts.
^ Fuel level is more than 10 percent.
^ Fuel ethanol composition less than 88 percent.

CONDITIONS FOR SETTING THE DTC
HO2S 2 voltage is more than 1042 mV for 50 seconds.

ACTION TAKEN WHEN THE DTC SETS
^ The Malfunction Indicator Lamp (MIL) will illuminate after 2 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 is stored.

CONDITIONS FOR CLEARING THE MIL/DTC
^ The MIL will turn OFF after 3 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.
^ A scan tool can clear the DTCs.

DIAGNOSTIC AIDS

IMPORTANT: Never solder the HO2S wires. For proper wire and connector repair refer to Wiring Repairs or Connector Repairs in Diagrams.

Inspect the following items:
^ The fuel pressure-If the pressure is too high, the system will run rich. The PCM can compensate for some increase. However, if the pressure gets too high, the DTC P0138 may set. Refer to Fuel System Diagnosis. Component Tests and General Diagnostics
^ A rich injector-Perform an Injector Balance Test. Refer to Fuel Injector Balance Test. Component Tests and General Diagnostics
^ A leaking injector-Refer to Fuel Injector Balance Test. Component Tests and General Diagnostics
^ Fuel contaminated oil.
^ EVAP canister purge-Check for a fuel saturation. If full of fuel, check the canister control and hoses. Refer to Evaporative Emission (EVAP) Control System Diagnosis. Component Tests and General Diagnostics
^ The TP sensor-An intermittent TP sensor output causes the system to run rich due to a false indication of the throttle moving.
^ False rich indication due to silicon contamination of the heated oxygen sensor-This DTC, accompanied by a lean driveability condition and a powdery white deposit on the sensor, may indicate a false rich indication.

An intermittent may be caused by any of the following conditions:
^ A poor connection
^ Rubbed through wire insulation
^ A broken wire inside the insulation

Thoroughly check any circuitry that is suspected of causing the intermittent complaint. Refer to Testing for Intermittent and Poor Connections in Diagrams.

If a repair is necessary, then refer to Wiring Repairs or Connector Repairs in Diagrams.

Diagnostic Chart (Part 1 Of 2):

Diagnostic Chart (Part 2 Of 2):

TEST DESCRIPTION
The numbers below refer to the step numbers on the diagnostic table.
2. In order to determine if the engine is rich during De-Acceleration Fuel Cut-Off (DFCO) operate the vehicle up to highway speed conditions and release the accelerator pedal, allowing the vehicle to coast in gear. Monitor the scan tool HO2S voltage and the DFCO parameter. A rich condition will cause the HO2S voltage to be more than 468 mV during DFCO.
5. Monitor the HO2S voltage of the opposite bank sensor. If the voltage activity of the opposite bank sensor is similar to the voltage activity of the suspect sensor, check for rich conditions that would affect both cylinder banks. An opposite bank sensor with normal HO2S voltage activity indicates the suspect HO2S is defective, or a rich condition exists only on the suspect HO2S cylinder bank.
6. This step checks the HO2S HIGH signal circuit for a short to voltage.
8. An HO2S contaminated by silicon will have a white, powdery deposit on the portion of the HO2S that is exposed to the exhaust stream. The usual cause of silica contamination is the use of unapproved silicon RTV engine gasket material or the use of silicon-based sprays or fluids within the engine. If the cause of this contamination is not corrected, the replacement HO2S will also become contaminated.