Refer to
Heated Oxygen Sensors
Circuit Description
To control emissions of Hydrocarbons (HC), Carbon Monoxide (CO), and Oxides of Nitrogen (NOx), a three-way catalytic converter is used. The catalyst within the converter promotes a chemical reaction which oxidizes the HC and CO present in the exhaust gas, converting them into harmless water vapor and carbon dioxide. The catalyst also reduces NOx, converting it to nitrogen. The PCM has the ability to monitor this process using the HO2S 1 and the HO2S 2 heated oxygen sensors. The HO2S 1 sensor produces an output signal which indicates the amount of oxygen present in the exhaust gas entering the three-way catalytic converter. The HO2S 2 sensor produces an output signal which indicates the oxygen storage capacity of the catalyst this in turn indicates the catalysts ability to convert exhaust gases efficiently. If the catalyst is operating efficiently, the HO2S 1 signal will be far more active than that produced by the HO2S 2 sensor. If the HO2S 2 signal voltage remains excessively low for an extended period of time, DTC P0137 will be set.
Conditions for Setting the DTC
| • | No active misfire, fuel injector circuit, TP sensor, EVAP, IAT sensor, MAP sensor, Fuel trim, EGR, ECT sensor, MAF sensor or CKP sensor DTC(s) present. |
| • | Closed loop commanded air/fuel ratio is between 14.4 and 14.9. |
| • | Throttle angle is between 5% and 40%. |
| • | Engine coolant temperature greater than 75°C (167°F). |
| • | HO2S 2 signal voltage remains below 100 mV during normal closed loop operation. |
OR
| • | HO2S 2 signal voltage remains below 100 mV during power enrichment mode fuel control operation. |
| • | Either condition for up to 50 seconds. |
Action Taken When the DTC Sets
| • | The PCM will illuminate the malfunction indicator lamp (MIL) during the second consecutive trip in which the diagnostic test has been run and failed. |
| • | The PCM will store conditions which were present when the DTC set as Freeze Frame and Failure Records data. |
Conditions for Clearing the MIL/DTC
| • | The PCM will turn OFF the MIL during the third consecutive trip in which the diagnostic has been run and passed. |
| • | The History DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction. |
| • | The DTC can be cleared by using the scan tool. |
Diagnostic Aids
Check for the following conditions:
| • | Heated oxygen sensor wiring. The sensor pigtail may be mispositioned and contacting the exhaust system. |
| • | Poor PCM to engine grounds. |
| • | Fuel pressure. A condition which causes a lean exhaust can cause DTC P0137 to set. The system will go lean if pressure is too low. The PCM can compensate for some decrease. However, if fuel pressure is too low, a DTC P0137 may be set. Refer to Fuel System Diagnosis. |
| • | Lean injector(s). Perform Injector Balance Test. |
| • | Vacuum leaks. Check for disconnected or damaged vacuum hoses and for vacuum leaks at the intake manifold, throttle body, EGR system, and CRANKCASE VENTILATION system. |
| • | Exhaust leaks. An exhaust leak may cause outside air to be pulled into the exhaust gas stream past the HO2S, causing the DTC P0137 to set. Check for exhaust leaks near the HO2S 2 sensor. |
| • | MAF sensor. Disconnect the MAF sensor and see if the condition is corrected. If so, replace MAF sensor. |
| • | Fuel contamination. Water, even in small amounts, can be delivered to the fuel injectors. The water can cause a lean exhaust to be indicated. Excessive alcohol in the fuel can also cause this condition. Refer to Fuel System Diagnosis for procedure to check for fuel contamination. |
Test Description
Number(s) below refer to the step number(s) on the Diagnostic Chart.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 | Was the Powertrain On-Board Diagnostic System Check performed? | -- | Go to Powertrain OBD System Check | |
2 |
Does the HO2S 2 voltage remain below the specified value? | 100 mV | ||
Does scan tool indicate DTC P0137 failed this ignition? | -- | Go to Diagnostic Aids | ||
4 | Disconnect HO2S 2 and jumper the HO2S 2 low circuit (PCM side) to ground. Does scan tool indicate HO2S 2 voltage near the specified value? | 450 mV | Go to Diagnostic Aids | |
5 | Turn off the ignition, disconnect the PCM, and check the HO2S 2 signal circuit for a short to ground or a short to the sensor ground circuit. Is the HO2S 2 signal circuit shorted? | -- | ||
6 | Repair the HO2S 2 signal circuit. Refer to Heated Oxygen Sensor (HO2S) Repair in Repair Procedures Electrical Diagnosis section 8A. Is action complete? | -- | -- | |
Replace the PCM. Important: The replacement PCM must be programmed. Refer to PCM Replacement/Programming. Is action complete? | -- | -- | ||
8 |
Does the scan tool indicate DTC P0137 failed this ignition? | -- | Repair complete |
