P0137
DTC P0137 HO2S Circuit Low Voltage Sensor 2
Circuit Description
The HO2S 2, located in the exhaust stream past the catalytic converter, produces an output signal proportional to the oxygen storage capacity of the catalytic converter. The PCM uses this signal to measure the ability of the catalytic converter to convert the exhaust emissions effectively. When the catalytic converter is functioning properly, the HO2S 2 signal is much less active than the signal produced by the front oxygen sensor 1 (O2S 1).
Conditions for Running the DTC
- There are no active manifold absolute pressure (MAP) DTCs.
- There are no active intake air temperature (IAT) DTCs.
- There are no active engine coolant temperature (ECT) DTCs.
- There are no active throttle position (TP) DTCs.
- There are no active fuel trim DTCs.
- There are no active injector control DTCs.
- There are no active misfire DTCs.
- There are no active crankshaft position (CKP) DTCs.
- There are no active evaporative emissions (EVAP) DTCs.
- There are no active idle air control (IAC) DTCs.
- There are no active PCM memory DTCs.
- The air flow is more than 5.5 grams per second.
- The engine coolant temperature (ECT) is more than 40° C (104° F).
- The throttle position (TP) angle is between 5 - 50 percent for 4 seconds.
- The above conditions are met for 140 seconds.
Conditions for Setting the DTC
HO2S 2 remains below 22 mV for 150 seconds.
Action Taken When the DTC Sets
- The control module illuminates the malfunction indicator lamp (MIL) if a failure is detected during 2 consecutive key cycles.
- The control module sets the DTC and records the operating conditions at the time the diagnostic failed. The failure information is recorded in the scan tool's Freeze Frame and Failure Records.
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.
- The DTCs can be cleared using the scan tool Clear Information function.
Diagnostic Aids
Whenever the oxygen sensor pigtail wiring, connector or terminal are damaged, the entire oxygen sensor assembly must be replaced. Do not attempt to repair the wiring, connector or terminals. In order for the 02S to function properly, the O2S must have a clean air reference. This clean air reference is obtained by way of the oxygen sensor wires. Any attempt to repair the wires, connectors or terminals could result in the obstruction of the air reference and degrade the oxygen sensors performance.
Rubbed through wire insulation or a wire contacting the exhaust may cause an intermittent fault to occur.
Check for the following conditions:
- The exhaust system - Inspect the exhaust system for leaks. Check the exhaust between the three-way catalytic converter and the flange for leaks, for corrosion, or for loose or missing hardware. Repair the exhaust as necessary.
- A poor connection or damaged harness - Inspect the harness for a short to ground in the rear HO2S 2 high circuit. Examine the connectors for improper mating or broken locks. Ensure that the HO2S 2 pigtail is not contacting the exhaust.
- An intermittent test - With the ignition ON, observe the rear HO2S 2 on the scan tool while moving any related connectors and wiring harnesses. If the fault is induced, the rear HO2S 2 display will change. This may help isolate the location of the malfunction.
Steps 1 - 4:
Steps 5 - 6:
Steps 7 - 11:
Test Description
The numbers below refer to the step numbers on the diagnostic table.
2. In order to determine if the engine is lean during power enrichment operate the vehicle under higher throttle/acceleration conditions while monitoring scan tool HO2S voltage and the power enrichment parameter. A lean condition will cause HO2S voltage to be less than 598 mV during power enrichment.
5. Monitor the HO2S voltage of the opposite bank sensor. If the voltage activity of the opposite bank sensor is similar to the voltage activity of the suspect sensor check for lean conditions that would affect both cylinder banks. An opposite bank sensor with normal HO2S voltage activity indicates the suspect HO2S needs replacement or a lean condition exists only on the suspect HO2S cylinder bank.