Diagnostic Instructions
| • | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. |
| • | Review Strategy Based Diagnosis for an overview of the diagnostic approach. |
| • | Diagnostic Procedure Instructions provides an overview of each diagnostic category. |
DTC Descriptors
DTC P0136: HO2S Circuit Sensor 2DTC P0137: HO2S Circuit Low Voltage Sensor 2
DTC P0138: HO2S Circuit High Voltage Sensor 2
Diagnostic Fault Information
Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance |
|---|---|---|---|---|
HO2S 2 Signal | P0136, P0137 | P0136, P0137 | P0136, P0138, P0606 | P0137 |
Low Reference | -- | P0136, P0137 | -- | P0137 |
Typical Scan Tool Data
Circuit | Short to Ground | Open | Short to Voltage |
|---|---|---|---|
Operating Conditions: Engine operating in Closed Loop with high exhaust system temperatures Parameter Normal Range: Fluctuates above and below 350-500 mV | |||
HO2S 2 Signal | 15 mV | 55 mV* | 1,275 mV |
Low Reference | -- | 55 mV* | -- |
*Voltage varies slightly with sensor/exhaust system temperature | |||
Circuit Description
The heated oxygen sensor (HO2S) sensor 2 circuit diagnostics 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.
The HO2S utilizes the following circuits:
| • | A signal circuit |
| • | A low reference circuit |
| • | An ignition 1 voltage circuit |
| • | A heater control circuit |
Conditions for Running the DTC
P0136, P0137, or P0138
| • | DTC P0031, P0032, P0037, P0038, P0100, P0101, P0102, P0103, P0110, P0112, P0113, P0115, P0117, P0118, P0120, P0121, P0122, P0123, P0125, P0171, P0172, P0300-P0304, P0335, P0340, P0341, P0385, P0441, P0455, P0456, P0500, P2195, P2196, P2A00 are not set. |
| • | The battery voltage is greater than 11 volts. |
| • | The engine coolant temperature (ECT) is greater than or equal to 75°C (167°F). |
| • | The engine speed is between 1,600-4,000 RPM. |
| • | The engine is operating in Closed Loop fuel control. |
| • | DTCs P0136, P0137, and P0138 run continuously when the above conditions are met. |
P0137
The target air fuel ratio is RICH.
P0138
The target air fuel ratio is LEAN.
Conditions for Setting the DTC
P0136
| • | The average HO2S 2 voltage is greater than or equal to 600 mV. |
| OR |
| • | The average HO2S 2 voltage is less than or equal to 250 mV. |
P0137
The average HO2S 2 voltage is less than 250 mV for greater than 30 seconds.
P0138
The average HO2S 2 voltage is greater than 590 mV for greater than 30 seconds.
Action Taken when the DTC Sets
DTCs P0136, P0137, and P0138 are Type B DTCs.
Conditions for Clearing the MIL/DTC
DTCs P0136, P0137, and P0138 are Type B DTCs.
Reference Information
Schematic Reference
Connector End View Reference
Electrical Information Reference
DTC Type Reference
Powertrain Diagnostic Trouble Code (DTC) Type Definitions
Scan Tool Reference
Control Module References for scan tool information
Circuit/System Verification
- Engine running at normal operating temperature and the exhaust system hot, observe the scan tool HO2S 2 voltage parameter. The reading should fluctuate between 250-650 mV.
- Operate the vehicle within the Conditions for Running the DTC to verify the DTC does not reset. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.
Important: To ensure the HO2S 2 is active, operate the engine at 2,000-2,500 RPM for 2 minutes, before performing the following verification.
Circuit/System Testing
- Ignition OFF, disconnect the harness connector located behind the front floor console.
- Ignition OFF, test for less than 10 ohms of resistance between the low reference circuit terminal 3 and ground G104.
- Connect the HO2S 2 electrical connector.
- Ignition ON, observe the HO2S 2 scan tool parameter is less than 1050 mV.
- Set the DMM to measure DC millivolts. Place the positive lead of the DMM on battery positive voltage, and the negative lead on the HO2S 2 sensor input circuit terminal 4 of the sensor connector.
- Ignition ON, verify the HO2S 2 scan tool parameter is greater than 1125 mV.
- If all the circuits test normal, replace the HO2S 2.
| ⇒ | If greater than the specified range, test the low reference circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the ECM. |
| ⇒ | If greater than the specified range, disconnect the HO2S 2 electrical. Verify the HO2S reading is between 35-55 mV. If greater than the specified range, test the signal circuit for a short to voltage. If the circuit tests normal, replace the HO2S 2. |
| ⇒ | If less than the specified range, test the signal circuit for an open/high resistance. If the circuit tests normal, replace the PCM. |
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
| • | Control Module References for control module replacement, setup, and programming |
