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 Bank 1 Sensor 1
DTC P2240: HO2S Pumping Current Control Circuit Bank 2 Sensor 1

### Circuit Description

The wide band heated oxygen sensor (HO2S) measures the amount of oxygen in the exhaust system and provides more information 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 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 voltage in the oxygen sensing cell. The ECM monitors the voltage variation in the sensing cell and attempts to keep the voltage constant by increasing or decreasing the amount of current flow, or oxygen ion flow, to the pumping cell. By measuring the amount of current required to maintain the voltage in the sensing cell, the ECM can determine the concentration of oxygen in the exhaust. The HO2S 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 fuel system is lean, the oxygen level will be high and the lambda signal will be high or greater than 1. When the fuel system is rich, the oxygen level will be low, and the lambda signal will be low or less than 1. The ECM uses this information to maintain the correct air/fuel ratio.

### Conditions for Running the DTC

#### Conditions 1

• | Before the ECM can report DTC P2237 or P2240 failed, DTCs P0101, P0121, P0122, P0123, P0221, P0222, P0223, P0335, P0336, and P0338 must run and pass.

• | DTCs P0030, P0031, P0032, P0050, P0051, P0052, P0133, P0135, P0153, or P0155 is not set.

• | The ignition voltage is between 11-18 volts.

• | The engine is operating in Closed Loop.

• | The HO2S 1 heater is at operating temperature.

• | The ECM is commanding the lambda greater than 1.03 or less than 0.97.

• | Greater than 200 grams of exhaust gas has passed.

• | DTC P2237 and P2240 run continuously once the above conditions are met for approximately 8 seconds.

#### Conditions 2

• | Before the ECM can report DTC P2237 or P2240 failed, DTCs P0101, P0121, P0122, P0123, P0221, P0222, P0223, P0335, P0336, and P0338 must run and pass.

• | The ignition voltage is between 11-18 volts.

• | The engine is operating in Closed Loop.

• | The HO2S 1 heater is at operating temperature.

• | The ECM detects the internal HO2S 1 signal voltage is between 1.49-1.51 volts.

• | The ECM is commanding the lambda rich and then lean periodically with a change of greater than 2 percent.

• | DTC P2237 and P2240 run continuously once the above conditions are met for greater than 1 second.

#### Conditions 3

• | Before the ECM can report DTC P2237 or P2240 failed, DTCs P0101, P0121, P0122, P0123, P0221, P0222, P0223, P0335, P0336, and P0338 must run and pass.

• | The ignition voltage is between 11-18 volts.

• | The HO2S 1 heater is at operating temperature.

• | The ECM is commanding decel fuel cut-off for greater than 3 seconds.

• | DTC P2237 and P2240 run continuously once the above conditions are met for greater than 2 seconds.

### Conditions for Setting the DTC

#### Conditions 1

• | The ECM detects the internal HO2S 1 signal voltage is between 1.49-1.51 volts while the desired lambda is above or below a threshold.

• | The above condition exists for greater than 4 seconds.

#### Conditions 2

• | The ECM stores the fuel trim control values after the above conditions are met. The ECM detects that the stored value and the current fuel trim control value deviates greater than 10 percent of the lambda value.

• | The above condition exists for greater than 4 seconds.

#### Conditions 3

• | The ECM detects the internal HO2S 1 signal voltage after a decel fuel shut-off is less than 1.7 volts.

• | The above condition exists for greater than 4 seconds.

### Action Taken when the DTC Sets

DTC P2237 and P2240 are Type B DTCs.

### Conditions for Clearing the MIL/DTC

DTC P2237 and P2240 are Type B DTCs.

### Diagnostic Aids

• | The HO2 wide band sensor does not toggle or switch like a switching HO2S. The HO2S 1 signal will be relatively stable for an idling engine.

• | The following table illustrates the typical voltages for the HO2S 1 circuits:

HO2S Circuit | Voltage
--- | ---

• | Ignition ON, Engine OFF

• | HO2S Disconnected

Heater Control | 4.6-5.0 V
Heater Supply Voltage | B+
High Signal | 2.6-3.1 V
Low Signal | 2.2-2.7 V
Pump Current | 2.5-3.0 V
Input Pump Current | 2.5-3.0 V

### 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

#### DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

#### Scan Tool Reference

Control Module References for scan tool information

### Circuit/System Verification

1. Engine idling at operating temperature. Observe the appropriate scan tool HO2S 1 Lambda parameter. Cycle the throttle from idle to wide open throttle 3 times within 5 seconds. The parameter should react immediately to the action.
2. 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 are captured in the Freeze Frame/Failure Records Data List.

### Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the appropriate HO2S 1.
2. Connect a 3A fused jumper wire between the high signal circuit terminal 3 and low signal circuit terminal 1.
3. Test for greater than 1 volt between the input pump current circuit terminal 4 and ground.

⇒ | If less than the specified range, test the input pump current circuit for an open. If the circuit tests normal, replace the ECM.

4. If all circuits test normal, replace the appropriate HO2S 1.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Heated Oxygen Sensor Replacement - Bank 1 Sensor 1

• | Heated Oxygen Sensor Replacement - Bank 2 Sensor 1

• | Control Module References for engine control module replacement, setup, and programming