DTC Advanced Diagnostics: P0138 (1.5L Engine)
DTC P0138: Secondary Heated Oxygen Sensor (Secondary HO2S (Sensor 2)) Circuit High Voltage
General Description
The secondary heated oxygen sensor (secondary HO2S (sensor 2)) detects the oxygen content in the exhaust gas downstream of the three way catalytic converter (TWC) during stoichiometric air/fuel ratio feedback control. The powertrain control module (PCM) controls the air/fuel ratio from the air/fuel ratio (A/F) sensor (sensor 1) output voltage to optimize the TWC efficiency. When power is applied to the secondary HO2S (sensor 2) heater, if the secondary HO2S (sensor 2) output voltage is high or the SO2_SG terminal voltage is high during feedback control, the PCM detects a malfunction and stores a DTC.
Monitor Execution, Sequence, Duration, DTC Type
| Execution | Continuous |
| Sequence | None |
| Duration | 5 seconds or more |
| DTC Type | Two drive cycles, MIL on |
Enable Conditions
| Condition | |
|---|---|
| State of the engine | Running |
Malfunction Threshold
Either of the conditions continues for at least 5 seconds:
- The secondary HO2S (sensor 2) output voltage (voltage difference between SO2 and SO2_SG terminals) is 3.28 V or more.
- The SO2_SG terminal voltage is 3.49 V or more.
Possible Cause
The causes shown may not be a complete list of all potential problems, and it is possible that there may be other causes.
- Secondary HO2S (sensor 2) SO2 line short to power
- Secondary HO2S (sensor 2) SO2 line open
- Secondary HO2S (sensor 2) SO2_SG line short to power
- Secondary HO2S (sensor 2) SO2_SG line open
- PCM internal circuit failure
Diagnosis Details
Conditions for setting the DTC
When a malfunction is detected during the first drive cycle, a Pending DTC is stored in the PCM memory. If the malfunction returns in the next (second) drive cycle, the MIL comes on and a Confirmed DTC, the freeze data, and the on-board snapshot are stored.
Conditions for clearing the DTC
The MIL is cleared if the malfunction does not return in three consecutive trips in which the diagnostic runs. The MIL, the Pending DTC, the Confirmed DTC, the freeze data, and the on-board snapshot can be cleared with the scan tool clear command.