DTC Advanced Diagnostics: P0138 (2019)
DTC P0138: Rear Secondary Heated Oxygen Sensor (Secondary HO2S (Bank 1, Sensor 2)) Circuit High Voltage
General Description
The rear secondary heated oxygen sensor (secondary HO2S (bank 1, sensor 2)) detects the oxygen content in the exhaust gas downstream of the rear warm up three way catalytic converter (WU-TWC) (bank 1) during stoichiometric air/fuel ratio feedback control. The powertrain control module (PCM) controls the air/fuel ratio from the rear air/fuel ratio (A/F) sensor (bank 1, sensor 1) output voltage so that the rear WU-TWC (bank 1) efficiency is optimized. When power is applied to the rear secondary HO2S (bank 1, sensor 2) heater, if the rear secondary HO2S (bank 1, sensor 2) output continues to exceed the upper limit used during feedback control, the PCM detects a malfunction and stores a DTC.
Monitor Execution, Sequence, Duration, DTC Type
| Execution | Continuous |
| Sequence | None |
| Duration | 5.0 seconds or more |
| DTC Type | Two drive cycles, MIL on |
Enable Conditions
| Condition | Minimum | Maximum |
|---|---|---|
| Elapsed time that secondary HO2S activity is not monitored after starting the engine | 20 seconds | - |
| Fuel feedback | Closed loop | |
Malfunction Threshold
The rear secondary HO2S (bank 1, sensor 2) output voltage [HO2S B1 S2] is 3.28 V or more for at least 5.0 seconds.
[ ]: HDS Parameter
Possible Cause
- Rear secondary HO2S (bank 1, sensor 2) circuit failure
- Rear secondary HO2S (bank 1, sensor 2) output rich stuck
Confirmation Procedure
Operating Condition
- Start the engine, and let it idle until the radiator fan comes on.
- Let the engine idle for at least 5 seconds.
- When the diagnosis does not finish at idle, drive immediately at a steady engine speed [ENGINE SPEED] between 1, 500 - 3, 000 rpm for at least 5 seconds.
- When the on-board snapshot is stored, drive the vehicle under those conditions instead of Driving Pattern step 3.
- Drive the vehicle in this manner only if the traffic regulations and ambient conditions allow.
With the HDS
None.
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 or by disconnecting the 12 volt battery.