P1138

DTC P1138: HO2S Circuit High Voltage During Decel Fuel Cut-Off (DFCO) Sensor 2

Wiring Diagram:

Circuit Description
The Heated Oxygen Sensor (HO2S) produces a voltage that varies between 100 - 900 mV under normal operating conditions. The Engine Control Module (ECM) produces a bias voltage on the HO2S signal circuit of 420 - 480 mV. The reference ground for the sensor is provided through the ECM. The ECM monitors the signal voltage to determine if the exhaust is lean or rich. The heated oxygen sensor voltage is high when the exhaust is rich, and low when the exhaust is lean. The ECM constantly monitors the HO2S signal during the Closed Loop operation. If the ECM detects an HO2S voltage that stays above a specified value during a fuel cutoff condition, the DTC will set.

Conditions for Setting the DTC
- Mass air flow is greater than 6 g/s.
- Ignition voltage is greater than 10 V.
- The engine is running for greater than 10 seconds.
- Power enrichment conditions are met.
- Coolant temperature is greater than 60 °C.
- HO2S filtered voltage is greater than 0.125 V.

Action Taken When the DTC Sets
- The Malfunction Indicator Lamp (MIL) will illuminate.
- The ECM 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.

Conditions for Clearing the MIL/DTC
- A history DTC will clear after 40 consecutive warm up cycles without a fault.
- The DTC(s) can be cleared by using the scan tool.
- Disconnecting the ECM battery feed for more than 10 seconds

Step 1-6:

Step 7-18:

Troubleshooting