Circuit Description
The DTC P0137 Heated Oxygen Sensor (HO2S) Circuit Low Voltage Sensor 2 diagnostic monitors the voltage on the signal circuit of the post catalyst oxygen sensor. In order to control emissions of hydrocarbons (HC), carbon monoxide (CO), and oxides of nitrogen (NOx), a 3-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 the HC and the CO into harmless water vapor and carbon dioxide. The catalyst also reduces NOx by converting the NOx to nitrogen. The powertrain control module (PCM) has the ability to monitor this process using the heated oxygen sensors HO2S 1 and HO2S 2. The HO2S 1 produces an output signal which indicates the amount of oxygen present in the exhaust gas entering the 3-way catalytic converter. The HO2S 2 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.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P0137 Heated Oxygen Sensor (HO2S) Circuit Low Voltage Sensor 2
Conditions for Running the DTC
| • | DTC P0031, P0032, P0100, P0101, P0102, P0103, P0110, P0112, P0113, P0115, P0117, P0118, P0120, P0121, P0122, P0123, P0125, P0171, P0172, P0300, P0301-P0304, P0335, P0340, P0341, P0385, P0441, P0442, P0446, P0456, P0500 are not set. |
| • | The engine coolant temperature (ECT) is more than or equal to 70°C (158°F). |
| • | The engine speed is more than 1,600 RPM. |
| • | The target air fuel ratio is RICH. |
| • | DTC P0137 runs continuously when the above conditions are met. |
Conditions for Setting the DTC
The average HO2S 2 voltage is less than 250 mV for more than 30 seconds.
Action Taken When the DTC Sets
| • | The PCM illuminates the malfunction indicator lamp (MIL). |
| • | The PCM stores the conditions which were present when the DTC set as Freeze Frame data. |
| • | The PCM will turn the HO2S 2 heater OFF. |
Conditions for Clearing the MIL/DTC
| • | The PCM turns OFF the MIL on the third consecutive trip cycle during which the diagnostic has been run and the fault condition is no longer present. |
| • | A DTC clears after 40 consecutive warm-up cycles have occurred without a fault. |
| • | A DTC can be cleared by using the scan tool Clear DTC Information function. |
Diagnostic Aids
Check for the following conditions:
| • | The HO2S 2 input voltage on a cold sensor, ignition ON with the engine OFF, is approximately 55 mV. |
| • | Inspect for an exhaust system leak near the HO2S 2 . Fresh air entering the exhaust flow near the sensor can cause a false low voltage input. |
| • | Inspect the wiring harness for damage. If the harness appears to be OK, observe the HO2S 2 display on the scan tool while moving the connectors and the wiring harnesses related to the sensor. A change in the HO2S 2 display will indicate the location of the fault. |
| • | If a DTC P0137 is intermittent, driving the vehicle under the conditions outlined in the Inspection/Maintenance (I/M) section can verify whether the fault is present. Refer to Inspection/Maintenance Heated Oxygen Sensor/Oxygen Sensor System Set . |
| • | An intermittent malfunction may be caused by fault in the HO2S circuit sensor electrical circuit. Inspect the wiring harness and components for an intermittent condition. Refer to Intermittent Conditions . |
| • | Repair any electrical circuit faults that were found. Refer to Wiring Repairs in Wiring Systems. |
The information included in the Freeze Frame data can be useful in determining the vehicle operating conditions when the DTC first set.
Test Description
The numbers below refer to the step numbers in the diagnostic table.
-
The Diagnostic System Check - Vehicle prompts the technician to complete some basic checks and store the Freeze Frame data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored in the scan tool for later reference.
-
This step determines if the DTC P0137 is the result of a hard failure or an intermittent condition.
-
In this step the DMM is used as a low current voltage source taking the place of the HO2S. If the HO2S 2 input circuit and the PCM are good, the scan tool will display approximately 1,275 mV.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics Connector End View Reference: Powertrain Control Module Connector End Views or Engine Controls Connector End Views | ||||
Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | Go to Diagnostic System Check - Vehicle in Vehicle DTC Information | |
Does DTC P0137 set? | -- | Go to Step 3 | Go to Diagnostic Aids | |
Is the voltage more than the specified value? | 1125 mV | Go to Step 4 | Go to Step 5 | |
4 |
Does the test lamp illuminate? | -- | Go to Step 7 | Go to Step 6 |
5 |
Did you find and correct the condition? | -- | Go to Step 9 | Go to Step 8 |
6 | Repair the open in the HO2S 2 ground circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 9 | -- |
7 | Replace the HO2S 2. Refer to Heated Oxygen Sensor 2 Replacement . Did you complete the replacement? | -- | Go to Step 9 | -- |
8 | Replace the PCM. Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming. Did you complete the replacement? | -- | Go to Step 9 | -- |
9 |
Does the DTC run and pass? | -- | Go to Step 10 | Go to Step 2 |
10 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | -- | Go to Diagnostic Trouble Code (DTC) List - Vehicle in Vehicle DTC Information | System OK |
