P0137

Heated Oxygen Sensor 2 (HO2S 2) Circuit:

Circuit Description
The Heated Oxygen Sensor 2 (HO2S 2), located in the exhaust stream past the catalytic converter produces an output signal relative to the oxygen storage capacity of the catalytic converter. The Powertrain Control Module (PCM) can then determine the catalytic converter's ability to convert exhaust emissions effectively. The HO2S 2 signal will be far less active than the signal produced by the front Oxygen Sensor 1 (O2S 1).

Conditions for Setting the DTC
- The Throttle Position (TP) sensor is between 9% and 50 %
- The Air Fuel (A/F) Ratio is between 14.5:1 and 14.7:1
- The engine coolant temperature is greater than 70°C (158°F)
- The vehicle is in "Closed Loop"
- The above conditions are met for 50 seconds
- The HO2S 2 remains below 22 mV for 68 seconds
- The engine run time is greater than 25 seconds
- One or more of the following DTCs are not set, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0300-P0304, P0506, P0507, P1406, P1441.

Action Taken When the DTC Sets
- The Malfunction Indicator Lamp (MIL) will illuminate after two consecutive ignition cycles in which the diagnostic runs with the fault active.
- The PCM 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
- The MIL will turn "OFF" after three 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.
- DTCs can be cleared by using a scan tool.

NOTE: 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 O2S 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 sensor's performance.
An intermittent may be caused by a rubbed through wire insulation or a wire contacting the exhaust.

Diagnostic Aids
Check for:
- Exhaust system - Inspect the exhaust system for leaks. Check exhaust between three way catalytic converter and flange for leaks, corrosion, or for loose or missing hardware and repair as necessary.
- Poor connection or damaged harness - Inspect the harness for a short to ground in rear HO2S 2 high circuit, improper mating, or broken locks. Ensure that the HO2S 2 pigtail is not contacting the exhaust.
- Intermittent test - Observe the rear HO2S 2 on the scan tool while moving related connectors and wiring harness with the key "ON." Whenever the fault is induced, the rear HO2S 2 display will change. This may help isolate the location of the malfunction.

DTC P0137 - Heated Oxygen Sensor (HO2S) Circuit Low Voltage Sensor 2:

Test Description
Numbers below refer to the step numbers on the Diagnostic Table.
1. The OBD System Check prompts the Technician to complete some basic checks and store the Freeze Frame Data and the Failure records on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. This information on the scan tool can be referred to later.
2. This step determines if DTC PO137 is the result of a hard fault or an intermittent condition.
4. Jumpering the rear HO2S 2 low circuit to ground is necessary to allow the PCM to display the supplied bias voltage. Whenever the voltage is between 0.35 and 0.55 volt, then the wiring and PCM are OK.
6. Before replacing the PCM, check terminals for improper mating, broken locks, or physical damage to the wiring harness. Replacement PCM must be reprogrammed. Refer to the latest Techline information for programming procedures.