P0137

DTC P0137 Oxygen Sensor 2 (O2S2) Low Voltage

Circuit Diagram:

Circuit Description
In order to control emissions, a catalytic converter is used to convert harmful emissions into harmless water vapor and carbon dioxide. The Engine Control Module (ECM) has the ability to monitor this process by using a Oxygen sensor 2 (O2S2). The O2S2, located in the exhaust stream past the catalytic converter, produces an output signal which indicates the storage capacity of the catalyst. This in turn indicates the catalyst's ability to convert exhaust emissions effectively. If the catalyst is functioning properly, the O2S2 signal will be far less active than the signal produced by the Oxygen sensor 1 (O2S1). If the O2S2 pigtail wiring, connector, or terminal is damaged, the entire O2S2 assembly must be replaced. Do not attempt to repair the wiring, connector, or terminals. In order for the sensor to function properly, it must have a clean air reference provided to it. This clean air reference is obtained by way of the O2S2 wire(s). Any attempt to repair the wires, connector, or terminals could result in the obstruction of the air reference and degrade the O2S2 performance.

Conditions for Setting the DTC
- O2S2 voltage is less than 0.052 volt in Closed Loop control or less than 0.35 volt in Power Enrichment (PE) mode.
- Engine Coolant Temperature (ECT) is greater than 60 °C (140 °F).
- System voltage is greater than 10 volts.
- Closed Loop test: 3 seconds delay after in Closed Loop and air flow is greater than 9 g/sec.
- Power Enrichment test: Air/Fuel ration is less than or equal to 13.5 and 2 seconds delay after in Power Enrichment mode.
- DTCs P0106, P0107, P0108, P0117, P0118, P0122, P0123, P0171, P0172, P0201, P0202, P0203, P0204, P0300, P0336, P0337, P0351, P0352, P0141, P0401, P0402, P0404, P0405, P0406, P0502, P0506, P0507, P1404, P1441 and P0443 are not set.

Action Taken When the DTC Sets
- The Malfunction Indicator Lamp (MIL) will illuminate.
- The ECM 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 four 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 DTC(s) can be cleared by using the scan tool.
- Disconnecting the ECM battery feed for more than 10 seconds.

Diagnostic Aids
An intermittent may be caused by rubbed-through wire insulation or a wire contacting the exhaust. Check for the following conditions:
- Exhaust system - Inspect the exhaust system for leaks. Check the exhaust between the three-way catalytic converter and the flange for leaks, corrosion, or for loose or missing hardware and repair as necessary.
- Poor connection or damaged harness - Ensure that the O2S2 pigtail is not contacting the exhaust. Check for the following conditions:
- Improper mating
- Broken locks
- Improperly formed
- Damaged terminals
- Poor terminal-to-wire connection
- Damaged harness
- Intermittent test - Observe the O2S2 on the scan tool while moving related connections and the wiring harness with the ignition ON. If the failure is induced, the O2S2 display will change. This may help isolate the location of the malfunction.

Test Description
Number(s) below refer to the step number(s) on the Diagnostic Table.
1. The On-Board Diagnostic (OBD II) System Check prompts the technician to complete some basic checks and store the freeze frame and failure records data on the scan tool if applicable. This creates an electronic copy of the data taken when the malfunction occurred. The information is then stored on the scan tool for later reference.
2. This step determines if DTC P0137 is the result of a hard failure or an intermittent condition.
4. Jumping the O2S2 low circuit, terminal 2 to ground is necessary to allow the ECM to display the supplied bias voltage. If the voltage is between 0.35 and 0.55 volt, then the wiring and ECM are OK.
6. The replacement ECM must be reprogrammed. Refer to the latest Techline procedure for ECM reprogramming.

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