For 1990-2009 cars
Engine Controls Components
Power, Ground, HO2S 2, and O2S 1
OBD II Symbol Description Notice
Powertrain Control Module Connector End Views
Handling ESD Sensitive Parts Notice

### Circuit Description

In order to control emissions, a catalytic converter converts any harmful exhaust emissions into harmless 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 is located in the exhaust stream past the catalytic converter. The sensor 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 correctly, the HO2S 2 signal will be far less active than the signal produced by the front oxygen sensor (O2S 1).

### Conditions for Running the DTC

• | The following DTCs are not set: 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.

• | 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 more than 10 seconds.

### Conditions For Setting The DTC

The HO2S 2 voltage is more than 648 mV for more than 10 seconds. The diagnostic then runs for 11 seconds to complete 1 test after a 10 second delay .

### 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 stores.

### 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.

• | Use a scan tool to clear the DTCs.

### Diagnostic Aids

• | An overly rich exhaust may load the catalyst causing high HO2S 2 signal voltages.

• | Silicone contamination of HO2S 2 could cause a false rich condition . A powdery white deposit on the sensor indicates this condition.

• | If there is an internal short in the HO2S 2, the sensor voltage displayed on a scan tool will be over 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 changes from more than 1000 mV to around 450 mV .

• | Observe the HO2S 2 on a scan tool while moving related connectors and the wiring harness with the ignition on. If the malfunction is induced, the HO2S 2 display will change. This should help isolate the location of the malfunction.

• | 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 connection

• | A rubbed through wire insulation

• | A broken wire inside the insulation

Do not attempt to repair the HO2S 2. Replace the entire HO2S 2 assembly if the following conditions exist:

• | Any damaged wiring

• | A damaged connector

• | Any damaged terminals

Obstruction of the air reference and degraded HO2S 2 performance can result from any attempt to repair the above conditions.

The HO2S 2 must have a clean air reference in order for the sensor to function correctly. This clean air reference is obtained by the HO2S 2 wires.

### Test Description

The numbers below refer to step numbers on the diagnostic table.

1. This step determines if DTC P1138 is the result of a hard malfunction or an intermittent condition.

2. 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 a sensor voltage of less than 100 mV. If the signal voltage is still high, the this indicates that the PCM is malfunctioning.

3. The replacement PCM must be programmed and the Crankshaft Position System Variation Learn procedure must be performed.

#### DTC P1138-HO2S Circuit High Voltage During Decel Fuel Cutoff Sensor 2

Step | Action | Values | Yes | No
--- | --- | --- | --- | ---
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | Go to Step 2 | Go to Powertrain On Board Diagnostic (OBD) System Check
2 | Use a scan tool in order to observe the HO2S 2 voltage. Is the voltage more than the specified value? | 1042 mV | Go to Step 4 | Go to Step 3
3 |

1. Operate the vehicle within the Freeze Frame conditions and the Conditions for Running the DTC as specified in the supporting text.
2. Use a scan tool in order to observe the HO2S 2 voltage.

Is the voltage more than the specified value?

1042 mV

Go to Step 4

Go to Diagnostic Aids

4 |

1. Turn off the ignition.
2. Disconnect the PCM.

Caution: Avoid contact with moving parts and hot surfaces while working around a running engine in order to prevent physical injury.

3. Disconnect the HO2S 2 connector.
4. Turn on the ignition, leaving the engine off.
5. Use a DMM in order to measure the voltage from the signal circuit of the HO2S 2 to ground.

Does the voltage equal the specified value?

0 V

Go to Step 5

Go to Step 6

5 |

1. Connect a jumper wire from the following circuits to ground at the HO2S 2 connector:

• | The signal circuit

• | The Low circuit

2. Use a scan tool in order to observe the HO2S 2 voltage.

Is the voltage less than the specified value?

100 mV

Go to Step 7

Go to Step 8

6 | Repair a short to voltage in the HO2S 2 signal circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 9 | --
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. Refer to Heated Oxygen Sensor Replacement . Did you complete the repair? | -- | Go to Step 9 | --
8 | Important:: The replacement PCM must be reprogrammed. Refer to Powertrain Control Module Replacement/Programming . Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the repair? | -- | Go to Step 9 | --
9 |

1. Use a scan tool to clear the DTCs.
2. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC reset?

--

Go to Step 2

System OK