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 P2237 : HO2S Pumping Current Control Circuit Sensor 1
DTC P2243 : HO2S Reference Voltage Circuit Sensor 1
DTC P2251 : HO2S Low Reference Circuit Sensor 1
DTC P2626 : HO2S Pumping Current Trim Circuit Sensor 1

### Diagnostic Fault Information

Circuit | Short to Ground | Open/High Resistance | Short to Voltage
--- | --- | --- | ---
Heater Voltage Supply | P0030, P0130 | P0030, P0053, P0130, P0135 | --
Heater Low Control | P0031, P0130 | P0030, P0053, P0135 | P0032
Reference Voltage (Signal) | P0131 | P0130, P2243 | P0132
Low Reference (Ground) | P0130, P0136 | P0130, P2251 | P0132
Pump Current | P0130, P0131, P2237 | P2237 | P0132, P2237
Trim Current | P0130, P0131, P2626 | P2626 | P0132, P2626

### Circuit/System Description

The wide band heated oxygen sensor (HO2S) measures the amount of oxygen in the exhaust stream more quickly and accurately than the switching style HO2S. The wide band sensor consists of an oxygen sensing cell, an oxygen pumping cell, and a heater. The exhaust gas sample passes through a diffusion gap between the sensing cell and the pumping cell. The engine control module (ECM) supplies a signal voltage to the HO2S and uses this voltage as a reference to the amount of oxygen in the exhaust system. An electronic circuit within the ECM controls the pump current through the oxygen pumping cell in order to maintain a constant signal voltage. The ECM monitors the voltage variation on the signal circuit and attempts to keep the voltage constant by increasing or decreasing the amount of current flow or reversing the direction of the current flow to the pumping cell. By measuring the direction and amount of current required to maintain the signal voltage, the ECM can determine the concentration of oxygen in the exhaust. The signal voltage is displayed as a lambda value. A lambda value of 1 is equal to a stoichiometric air fuel ratio of 14.7:1. Under normal operating conditions, the lambda value will remain around 1. When the system is lean, the oxygen level will be high and the lambda value will be high, or more than 1. When the system is rich, the oxygen level is low and the lambda value will be low, or less than 1. The ECM uses this information to maintain the proper air/fuel ratio.

### Conditions for Running the DTC

#### P2237

• | DTCs P0121, P0122, P0123, P0221, P0222, P0223, P0335, P0336, P0338 are not set.

• | The ignition voltage is between 10.7-18.1 volts.

• | The engine is running.

• | HO2S 1 voltage is between 1.48-1.52 volts.

• | HO2S 1 heater is at operating temperature.

• | HO2S 1 closed loop is active.

• | The catalyst temperature is stable.

• | DTC P2237 runs continuously when the above conditions are met for 2 seconds.

#### P2243

• | DTCs P0030, P0031, P0032 are not set.

• | The ignition voltage is between 10.7-18.1 volts.

• | The engine is running.

• | HO2S 1 heater is at operating temperature for at least 20 seconds.

• | HO2S 1 internal resistance is more than 570 ohms.

• | DTC P2243 runs continuously when the above conditions are met for 2 seconds.

#### P2251

• | DTCs P0030, P0031, P0032 are not set.

• | The ignition voltage is between 10.7-18.1 volts.

• | The engine is running.

• | The estimated exhaust temperature is less than 900°C (1,652°F).

• | The HO2S 1 voltage is between 1.47-1.53 volts.

• | The HO2S 1 heater temperature has been within the normal range for more than 20 seconds.

• | HO2S 1 internal resistance is more than 570 ohms.

• | The following are true for more than 30 seconds.

- | The HO2S 1 heater is ready.

- | The engine is running.

- | The ignition voltage is more than 11 volts.

• | DTC P2251 runs continuously when the above conditions are met for 10 minutes.

#### P2626

• | DTCs P0121, P0122, P0123, P0221, P0222, P0223, P0335, P0336, P0338 are not set.

• | The ignition voltage is between 10.7-8.1 volts.

• | The engine is running.

• | Fuel cut-off is true.

• | The estimated exhaust temperature is less than 750°C (1,382°F).

• | The HO2S 1 heater is at operating temperature.

• | DTC P2626 runs continuously when the above conditions are met for 4 seconds, or when the above conditions are met for 10 minutes if the fuel level is low.

### Conditions for Setting the DTC

#### P2237

• | The ECM detects that the pumping current circuit is open.

• | DTC P2237 sets within 4 seconds when the above condition is met continuously, or within 50 seconds when the above condition is met cumulatively.

#### P2243

• | The ECM detects that the HO2S 1 voltage is less than 0.2 volts or more than 4.7 volts.

• | DTC P2243 sets within 4 seconds when the above condition is met continuously, or within 50 seconds when the above condition is met cumulatively.

#### P2251

• | The ECM detects that the reference ground circuit is open.

• | DTC P2251 sets within 4 seconds when the above condition is met continuously, or within 50 seconds when the above condition is met cumulatively.

#### P2626

• | The ECM detects that the HO2S 1 voltage is more than 4.81 volts.

• | DTC P2626 sets within 4 seconds when the above condition is met continuously, or within 50 seconds when the above condition is met cumulatively.

### Action Taken When the DTC Sets

DTCs P2237, P2243, P2251, and P2626 are Type B DTCs.

### Conditions for Clearing the DTC

DTCs P2237, P2243, P2251, and P2626 are Type B DTCs.

### Reference Information

#### Schematic Reference

Engine Controls Schematics

#### Connector End View Reference

• | Engine Control Module Connector End Views

• | Engine Controls 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

• | Scan Tool Data List

• | Scan Tool Data Definitions

• | Scan Tool Output Controls

### 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 HO2S 1.
2. Ignition ON, test for 2.9 volts between the HO2S 1 High Signal circuit terminal 6 and ground.

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

⇒ | If less than the specified value, test the circuit for an open/high resistance or a short to ground. If the circuit tests normal, replace the ECM.

3. Ignition ON, test for 2.5 volts between the HO2S 1 Low Signal circuit terminal and ground.

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

⇒ | If less than the specified value, test the circuit for an open/high resistance or a short to ground. If the circuit tests normal, replace the ECM.

4. Ignition ON, test for 2.8 volts between the HO2S 1 Output Pump Current circuit terminal and ground.

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

⇒ | If less than the specified value, test the circuit for an open/high resistance or a short to ground. If the circuit tests normal, replace the ECM.

5. Ignition ON, test for 2.8 volts between the HO2S 1 Input Pump Current circuit terminal and ground.

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

⇒ | If less than the specified value, test the circuit for an open/high resistance or a short to ground. If the circuit tests normal, replace the ECM.

6. Ignition OFF, disconnect the ECM connector C1.
7. Ignition OFF, test for infinite ohms between each HO2S 1 circuit terminal and all other HO2S 1 circuit terminals.

⇒ | If less than the specified value, repair as necessary.

8. If the ECM and all circuits test normal, replace the HO2S 1.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Heated Oxygen Sensor 1 Replacement

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