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 provide an overview of each diagnostic category.

### DTC Descriptor

DTC P0136 00: HO2S Circuit Low Voltage Sensor 2

### Diagnostic Fault Information

Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
HO2S 2 Signal | P0136 00, P0137 00 | P0136 00, P0137 00 | P0136 00, P0138 00, P0606 00 | P0137 00
Low Reference | -- | P0136 00, P0137 00 | -- | P0137 00

### 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
Heated Oxygen Sensor (HO2S) 2 Signal | 15 mV | 55 mV* | 1275 mV
Low Reference | -- | 55 mV* | --
*Voltage varies slightly with sensor/exhaust system temperature

### Circuit/System Description

The heated oxygen sensor (HO2S) 2 circuit diagnostics monitors the voltage on the signal circuit of the post catalyst oxygen sensor. In order to control emissions of hydrocarbons, 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 hydrocarbons and CO present in the exhaust gas, converting the hydrocarbons and the CO into harmless water vapor and carbon dioxide. The catalyst also reduces NOx by converting the NOx to nitrogen. The engine control module (ECM) has the ability to monitor this process using the heated oxygen sensors HO2S 1 and heated oxygen sensor (HO2S) 2. The heated oxygen sensor (HO2S) 1 produces an output signal which indicates the amount of oxygen present in the exhaust gas entering the 3-way catalytic converter. The heated oxygen sensor (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 heated oxygen sensor (HO2S) 1 signal will be far more active than that produced by the heated oxygen sensor (HO2S) 2.

The HO2S utilizes the following circuits:

• | A signal circuit

• | A low reference circuit

• | An ignition voltage circuit

• | A heater control circuit

### Conditions for Running the DTC

#### P0136 00

• | DTC P0031 00, P0032 00, P0037 00, P0038 00, P0112 00, P0113 00, P0117 00, P0118 00, P0121 00, P0122 00, P0123 00, P0125 00, P0171 00, P0172 00, P0300-P0304 00, P0335 00, P0340 00, P0341 00, P0455 00, P0456 00, P0500 00, P2A00 00 are not set.

• | The battery voltage is greater than 11 V.

• | The engine coolant temperature (ECT) is greater than or equal to 75°C (167°F).

• | The engine speed is between 1600-4000 RPM.

• | The engine is operating in closed loop fuel control.

• | DTC P0136 00 runs once per drive cycle when the above conditions are met for 2 s.

### Conditions for Setting the DTC

#### P0136 00

• | The average heated oxygen sensor (HO2S) 2 voltage is greater than or equal to 600 mV.

| or

• | The average heated oxygen sensor (HO2S) 2 voltage is less than or equal to 250 mV.

### Action Taken When the DTC Sets

DTCs P0136 00 is a Type B DTCs.

### Conditions for Clearing the DTC

DTCs P0136 00 is a 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

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

• | Heated Oxygen Sensor 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

Note: You must perform the circuit/system verification before proceeding with circuit/system testing.

1. Ignition OFF, disconnect the harness connector at the B52B Heated Oxygen Sensor (HO2S).
2. Ignition OFF, measure for less than 5 Ω between the B52B Heated Oxygen Sensor (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 K20 Engine Control Module (ECM).

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

⇒ | If more than the specified value, test the appropriate B52B Heated Oxygen Sensor (HO2S) high signal circuit terminal 2 for a short to voltage. If the circuit tests normal, replace the K20 Engine Control Module (ECM).

⇒ | If less than the specified value, test the appropriate B52B Heated Oxygen Sensor (HO2S) high signal circuit terminal 2 for a short to ground. If the circuit tests normal, replace the K20 Engine Control Module (ECM).

4. Ignition ON, install a 3A fused jumper wire at the B52B Heated Oxygen Sensor (HO2S) high signal circuit terminal 2. Toggle the jumper wire between the B52B Heated Oxygen Sensor (HO2S) low signal circuit terminal 4 and battery voltage. Verify the appropriate scan tool HO2S 2 parameter toggles between 0 mV and approximately 1000 mV.

⇒ | If the appropriate scan tool B52B Heated Oxygen Sensor (HO2S) parameter does not toggle correctly, test the B52B Heated Oxygen Sensor (HO2S) high signal circuit terminal 2 for an open/high resistance. If the circuits test normal, replace the K20 Engine Control Module (ECM).

5. If all circuits test normal, replace the appropriate B52B Heated Oxygen Sensor (HO2S).

### Repair Instructions

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

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Heated Oxygen Sensor Replacement - Sensor 2

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