For 1990-2009 cars

### 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 P0137: HO2S Circuit Low Voltage Sensor 2
DTC P0138: HO2S Circuit High Voltage Sensor 2
DTC P0139: HO2S Circuit Slow Response Sensor 2
DTC P0140: HO2S Circuit Insufficient Activity Sensor 2
DTC P2270: HO2S Signal Stuck Lean Sensor 2
DTC P2271: HO2S Signal Stuck Rich Sensor 2
DTC P2A01: HO2S Performance Sensor 2

### Diagnostic Fault Information

Circuit | Short to Ground | Open | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
HO2S 2 Heater Voltage Supply | Opens fuse | P0036, P0037, P0141 | -- | P0141
HO2S 2 Heater Low Control | P0036, P0037, | P0036, P0037, P0141 | P0036, P0038, P0141 | P0141
HO2S 2 Signal | P0137 | P0140 | P0138 | P0139, P0140, P2A01, P2270, P2271
HO2S 2 Voltage Reference | Opens Fuse | P0140 | -- | --

### Circuit/System Description

Heated oxygen sensors (HO2S) are used for fuel control and post catalyst monitoring. Each HO2S compares the oxygen content of the surrounding air with the oxygen content in the exhaust stream. The HO2S must reach operating temperature to provide an accurate voltage signal. Heating elements inside the HO2S minimize the time required for the sensors to reach operating temperature. The engine control module (ECM) supplies the HO2S with a reference, or bias, voltage of about 450 mV. When the engine is first started, the ECM operates in Open Loop, ignoring the HO2S voltage signal. Once the HO2S reaches operating temperature and Closed Loop is achieved, the HO2S generates a voltage within a range of 0-1,000 mV that fluctuates above and below bias voltage. High HO2S voltage indicates a rich exhaust stream. Low HO2S voltage indicates a lean exhaust stream.

### Conditions for Running the DTC

#### P0137

• | DTCs P0036, P0037, P0038 P0102, P0103, P0136, P0137, P0138, P0139, P0140, P0141, P0443, P0458, P0459, P2270, P2271, P2A01 are not set.

• | The engine is running.

• | The mass air flow is more than 8 kg/h.

• | DTC P0137 runs once per drive cycle when the above conditions are met for 2 seconds.

#### P0138

• | DTCs P0036, P0037, P0038, P0136, P0137, P0138, P0139, P0140, P0141, P2270, P2271, P2A01 are not set.

• | The ignition is ON.

#### P0139

• | DTCs P000A, P000B, P0010, P0011, P0013, P0014, P0016, P0017, P0036, P0037, P0038, P0068, P0101, P0102, P0103, P0116, P0117, P0118, P0119, P0121, P0122, P0123, P0136, P0137, P0138, P0141, P0171, P0172, P0201, P0202, P0203, P0204, P0221, P0222, P0223, P0261, P0262, P0264, P0265, P0267, P0268, P0270, P0271, P0300, P0301, P0302, P0303, P0304, P0313, P0335, P0336, P0340, P0341, P0365, P0366, P0443, P0458, P0459, P0496, P0501, P1101, P2088, P2089, P2090, P2091, P2100, P2101, P2176, P2270, P2271, P2A01 are not set.

• | The ignition is ON.

• | The engine coolant temperature is hotter than 60°C (140°F).

• | The HO2S 2 signal voltage is more than 552 mV.

• | The mass air flow is between 5-400 kg/h.

• | The vehicle speed is between 19-31 kph (12-93 mph).

• | DTC P0139 runs once per ignition cycle when the above conditions are met for 1 second.

#### P0140

• | DTCs P000A, P000B, P0010, P0011, P0013, P0014, P0016, P0017, P0030, P0031, P0032, P0036, P0037, P0038, P0068, P0101, P0102, P0103, P0116, P0117, P0118, P0119, P0121, P0122, P0123, P0130, P0131, P0132, P0133, P0137, P0138, P0139, P0141, P0171, P0172, P0221, P0222, P0223, P0300, P0301, P0302, P0303, P0304, P0313, P0335, P0336, P0340, P0341, P0365, P0366, P0443, P0458, P0459, P0496, P1101, P2088, P2089, P2090, P2091, P2176, P2270, P2271, P2297, P2A00, P2A01 are not set.

• | The engine has been running for more than 5 minutes.

• | The engine coolant temperature is hotter than 75°C (167°F).

• | DTC P0140 runs continuously when the above conditions are met for 60 minutes.

#### P2270

• | DTCs P0036, P0037, P0038, P0137, P0138, P0140, P0141, P0443, P0458, P0459, P2232 are not set.

• | The engine is running.

• | The ignition voltage is more than 10.5 volts.

• | The HO2S 2 has been in Closed Loop for more than 10 seconds.

• | The DFCO is inactive.

• | The engine air flow has been between 5.56-33.33 g/sec for more than 3 seconds, and is currently more than 9.72 g/sec.

• | DTC P2270 runs continuously when the above conditions are met for 10 minutes.

#### P2271

• | DTCs P000A, P000B, P0010, P0011, P0013, P0014, P0016, P0017, P0030, P0031, P0032, P0036, P0037, P0038, P0068, P0101, P0102, P0103, P0116, P0117, P0118, P0119, P0121, P0122, P0123, P0130, P0131, P0132, P0133, P0137, P0138, P0139, P0141, P0171, P0172, P0221, P0222, P0223, P0300, P0301, P0302, P0303, P0304, P0313, P0335, P0336, P0340, P0341, P0365, P0366, P0443, P0458, P0459, P0496, P1101, P2088, P2089, P2090, P2091, P2176, P2270, P2271, P2297, P2A00, P2A01 are not set.

• | The engine has been running for more than 5 minutes.

• | The engine coolant temperature is hotter than 75°C (167°F).

• | DTC P2271 runs continuously when the above conditions are met for 10 minutes.

#### P2A01

• | DTCs P0036, P0037, P0038, P0068, P0101, P0102, P0103, P0136, P0137, P0138, P0139, P0140, P0141, P0171, P0172, P0201, P0202, P0203, P0204, P0261, P0262, P0264, P0265, P0267, P0268, P0270, P0271, P0300, P0301, P0302, P0303, P0304, P0313, P0443, P0458, P0459, P0496, P1101, P2270, P2271 are not set.

• | The ignition is ON.

• | Decel fuel cut-off is active.

• | The mass airflow is more than 10 grams per second.

• | DTC P2A01 runs continuously when the above conditions are met.

### Conditions for Setting the DTC

#### P0137

• | The ECM detects that the HO2S 2 voltage parameter is less than 24 mV.

• | DTC P0137 sets within 0.1 second during the lean test when the above condition is met.

#### P0138

• | The ECM detects that the HO2S 2 voltage is more than 1.2 V.

• | DTC P0138 sets when the above condition is met.

#### P0139

• | The ECM detects that the HO2S 2 has switched less than a calibrated number of times within a calibrated time period that depends on driving conditions.

• | DTC P0139 sets within 4 seconds when the above condition is met.

#### P0140

• | The ECM detects that the HO2S 2 voltage parameter is between 0.298-0.605 volt.

• | DTC P0140 sets within 4 seconds when the above condition is met for 60 seconds.

#### P2270

• | The ECM detects that the HO2S 2 voltage oscillations are slower than a calibrated value.

• | DTC P2270 sets within 4 seconds when the above condition is met continuously, or within 50 seconds when the above condition is met cumulatively.

#### P2271

• | The ECM detects that the HO2S 2 voltage oscillations are faster than a calibrated value.

• | DTC P2271 sets within 4 seconds when the above condition is met continuously, or within 50 seconds when the above condition is met cumulatively.

#### P2A01

• | The ECM detects that the HO2S 2 voltage is more than 0.151 V.

• | DTC P2A01 sets when the above condition is met.

### Action Taken When the DTC Sets

DTCs P0137, P0138, P0139, P0140, P2270, P2271, and P2A01 are Type B DTCs.

### Conditions for Clearing the MIL/DTC

DTCs P0137, P0138, P0139, P0140, P2270, P2271, and P2A01 are Type B DTCs.

### Reference Information

#### Schematic Reference

Engine Controls Schematics

#### Connector End View Reference

Component Connector End Views

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Heated Oxygen Sensor Wiring Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

#### Scan Tool Reference

Control Module References for scan tool information

### Circuit/System Verification

1. Clear the DTCs with a scan tool.
2. Operate the vehicle within the conditions for running and setting the DTC. The DTC should not set.

### Circuit/System Testing

You must perform the Circuit/System Verification before proceeding with Circuit/System Testing.

1. Ignition OFF, disconnect the harness connector at the HO2S.
2. Ignition OFF, measure for less than 5 ohms between the HO2S low signal circuit terminal 4 and ground.

⇒ | If more than the specified range, test the appropriate HO2S low signal circuit for an open/high resistance. If the circuit tests normal, replace the ECM.

3. Ignition ON, verify the appropriate scan tool HO2S parameter is approximately 450 mV.

⇒ | If more than the specified value, test the appropriate HO2S high signal circuit for a short to voltage. If the circuit tests normal, replace the ECM.

⇒ | If less than the specified value, test the appropriate HO2S high signal circuit for a short to ground. If the circuit tests normal, replace the ECM.

4. Ignition ON, install a 3A fused jumper wire at the HO2S high signal circuit terminal 2. Toggle the other end of the jumper wire between the HO2S low signal circuit terminal 4 and battery voltage. Verify the appropriate scan tool HO2S parameter toggles between 0 mV and approximately 5,000 mV.

⇒ | If the appropriate scan tool HO2S parameter does not toggle correctly, test the HO2S high signal circuit for an open/high resistance. If the circuits test normal, replace the ECM.

5. If all circuits test normal, replace the appropriate HO2S.

### Repair Instructions

Caution: Refer to Heated Oxygen Sensor Resistance Learn Reset Caution in the Preface section.

Note: For DTC P0131 and P0132, in order to ensure that the performance of the catalyst has not been affected by the fault that set this DTC, operate the vehicle within the Conditions for Running and setting DTC P0420, and verify that DTC P0420 runs and passes. Refer to DTC P0420.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Heated Oxygen Sensor Replacement - Sensor 1

• | Heated Oxygen Sensor Replacement - Sensor 2

• | Control Module References for ECM replacement, setup, and programming