Advanced Diagnostics
Advanced Diagnostics - 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 engine control module (ECM)/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. After current is applied to the secondary HO2S heater, if the secondary HO2S output continues to exceed the upper limit used during feedback control, the ECM/PCM detects a malfunction and stores a DTC.
Monitor Execution, Sequence, Duration, DTC Type, OBD Status
Enable Conditions
Malfunction Threshold
The secondary HO2S output voltage is 1.27 V or more for at least 5.0 seconds.
Confirmation Procedure
With the Driving Pattern
1. Start the engine, and let it idle until the radiator fan comes on.
2. Drive immediately at a steady engine speed between 1,500 - 3,000 rpm for at least 5 seconds.
- When freeze data is stored, drive the vehicle under those conditions instead of Driving Pattern step 2.
- Drive the vehicle in this manner only if the traffic regulations and ambient conditions allow.
Diagnosis Details
Conditions for setting the DTC
When a malfunction is detected during the first drive cycle, a Pending DTC is stored in the ECM/PCM memory. If the malfunction returns in the next (second) drive cycle, the MIL comes on and a Confirmed DTC and the freeze data 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, and the freeze data can be cleared with the scan tool Clear command or by disconnecting the battery.
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 engine control module (ECM)/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. After current is applied to the secondary HO2S heater, if the secondary HO2S output continues to exceed the upper limit used during feedback control, the ECM/PCM detects a malfunction and stores a DTC.
Monitor Execution, Sequence, Duration, DTC Type, OBD Status
Enable Conditions
Malfunction Threshold
The secondary HO2S output voltage is 1.27 V or more for at least 5.0 seconds.
Confirmation Procedure
With the Driving Pattern
1. Start the engine, and let it idle until the radiator fan comes on.
2. Drive immediately at a steady engine speed between 1,500 - 3,000 rpm for at least 5 seconds.
- When freeze data is stored, drive the vehicle under those conditions instead of Driving Pattern step 2.
- Drive the vehicle in this manner only if the traffic regulations and ambient conditions allow.
Diagnosis Details
Conditions for setting the DTC
When a malfunction is detected during the first drive cycle, a Pending DTC is stored in the ECM/PCM memory. If the malfunction returns in the next (second) drive cycle, the MIL comes on and a Confirmed DTC and the freeze data 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, and the freeze data can be cleared with the scan tool Clear command or by disconnecting the battery.
