Diagnostic Instructions

DTC Descriptors

DTC P2237: Heated Oxygen Sensor (HO2S) Pumping Current Control Circuit Sensor 1

DTC P2238: Heated Oxygen Sensor (HO2S) Pumping Current Control Circuit Low Voltage Sensor 1

DTC P2239: Heated Oxygen Sensor (HO2S) Pumping Current Control Circuit High Voltage Sensor 1

Diagnostic Fault Information

Circuit	Short to Ground	Open/High Resistance	Short to Voltage	Signal Performance
HO2S 1 Input	P2195, P2237, P2238	P2237, P2238	P2196, P2237, P2239	P2237, P2238, P2A00
Low Reference	P2196, P2237, P2239, P2252	P2237, P2238	P2196, P2237, P2238, P2253	P2237, P2238

Typical Scan Tool Data

HO2S 1

Circuit	Short to Ground	Open	Short to Voltage
Operating Conditions: Engine operating in Closed Loop Parameter Normal Range: Fluctuates between 3.2-3.4 volts
HO2S 1 Input	4.99 volts*	3.3-3.4 volts	0.00 volts*
Low Reference	4.99 volts*	3.3-3.4 volts	0.00 volts*
*Actual circuit voltage is not the same as scan tool displayed voltage

Circuit Description

The heated oxygen sensor (HO2S) 1 is a wide band or wide range design. As with all oxygen sensors, the wide band HO2S measures the amount of oxygen in the exhaust system, but provides more information than the typical 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 powertrain control module (PCM) 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 PCM controls the pump current through the oxygen pumping cell in order to maintain a constant voltage in the oxygen sensing cell. The PCM 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 PCM can determine the concentration of oxygen in the exhaust. The HO2S input signal is displayed as a voltage within the range of 1-5 volts, with a steady value of 3.2-3.3 volts equal to the air fuel ratio of 14.7:1. If the HO2S 1 input voltage is lower than the specified reference voltage, the PCM determines that the air/fuel ratio is richer than the theoretical air/fuel ratio and reduces the fuel. If the input voltage from the HO2S 1 is higher than the specified reference voltage, the PCM determines that the air/fuel ratio is leaner and increases the fuel. By repeating these operations, the PCM can adjust the air/fuel ratio in order to be closer to the theoretical air/fuel ratio. Control of the fuel delivery system as just described is known as Closed Loop operation.

The HO2S utilizes the following circuits:

Air Fuel Mixture	Exhaust O2 Content	HO2S 1 Output	Fuel System Response
Lean Mixture	High Oxygen	More Than 3.4 V	Rich Command
Rich Mixture	Low Oxygen	Less Than 3.2 V	Lean Command

Conditions for Running the DTC

Conditions for Setting the DTC

P2237

P2238

P2239

The HO2S 1 input voltage is greater than 4.5 volts for greater than 5 seconds.

Action Taken when the DTC Sets

DTCs  P2237, P2238, and P2239 are Type B DTCs.

Conditions for Clearing the MIL/DTC

DTCs  P2237, P2238, and P2239 are Type B DTCs.

Reference Information

Schematic Reference

Engine Controls Schematics

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

1. Engine running at normal operating temperature, observe the scan tool HO2S 1 voltage parameter. The reading should fluctuate between 3.2-3.4 volts.
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 you observed from the Freeze Frame/Failure Records data.

Circuit/System Testing

1. Ignition OFF, disconnect the harness connector of the HO2S 1.
2. Ignition ON, test for 3.4-3.6 volts between the HO2S 1 input circuit terminal 3 and ground.

⇒	If greater than the specified range, test the HO2S 1 input circuit for a short to voltage. If the circuit tests normal, replace the PCM.

⇒	If less than the specified range, test the HO2S 1 input circuit for an open/high resistance or a short to ground. If the circuit tests normal, replace the PCM.

3. If all the circuits test normal, replace the HO2S 1.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.