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.
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 |
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P2238 Heated Oxygen Sensor (HO2S) Pumping Current Control Circuit Low Voltage Sensor 1
Conditions for Running the DTC
| • | DTCs P0031, P0032, P0051, P0052, P0100, P0101, P0102, P0103, P0110, P0112, P0113, P0115, P0117, P0118, P0120, P0121, P0122, P0123, P0125, P0171, P0172, P0220, P0222, P0223, P0300, P0301-P0304, P0335, P0340, P0341, P0385, P0441, P0455, P0456, P0500, P2135, P2195, P2196 are not set. |
| • | The battery voltage is more than 10.5 volts. |
| • | The engine coolant temperature (ECT) is more than 20°C (68°F). |
| • | The engine has been running more than 20 seconds. |
| • | DTC P2238 runs once per drive cycle when the above conditions have been met. |
Conditions for Setting the DTC
The HO2S input voltage is less than 0.5 volts for at least 5 seconds.
OR
The difference between the HO2S input voltage and the HO2S low reference voltage is less than 0.1 volts for at least 5 seconds.
Action Taken When the DTC Sets
| • | The PCM illuminates the malfunction indicator lamp (MIL) during the second key cycle in which the diagnostic trouble code (DTC) sets. |
| • | The PCM records the operating conditions at the time the diagnostic fails. This information is stored in the Freeze Frame buffer. |
Conditions for Clearing the MIL/DTC
| • | The PCM turns OFF the MIL after 3 consecutive trips without a fault. |
| • | The PCM clears a History DTC after 40 consecutive warm-up cycles without a fault. |
| • | Use the scan tool Clear DTC Information function. |
Diagnostic Aids
| • | The scan tool output control feature, Fuel Injector Modification, can be used at idle to check the oxygen sensor performance. Commanding the Fuel Injector Modification Commanded State to 25 percent should cause the HO2S 1 voltage to decrease to less than 3.0 V. Changing the Fuel Injector Modification Commanded State to -12 percent should cause the HO2S 1 voltage to increase to more than 3.35 V. An oxygen sensor that fails to respond accordingly may be faulty or contaminated. When performing the Fuel Injector Modification with the scan tool, the Loop Status will remain Open Loop and the Short Term FT will be fixed at 0 percent. |
| • | Check for a contaminated HO2S. Silicon contamination of the HO2S can cause a low signal voltage to be indicated. Silicon contamination is indicated by a powdery white deposit on the portion of the HO2S exposed to the exhaust stream. Before replacing the HO2S determine the cause of the contamination and correct the condition. |
| • | Verify the PCM to engine electrical grounds are OK. |
| • | An intermittent malfunction may be caused by fault in the HO2S 1 electrical circuit. Inspect the wiring harness and components for any intermittent conditions. Refer to Intermittent Conditions . |
The information included in the Freeze Frame data can be useful in determining the vehicle operating conditions when the DTC first set.
Test Description
The numbers below refer to the step numbers in the diagnostic table.
-
The Diagnostic System Check - Vehicle prompts the technician to complete some basic checks and store the Freeze Frame data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored in the scan tool for later reference.
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This step checks whether the malfunction that caused the DTC P2238 is still present. The HO2S 1 diagnostic can be monitored on the scan tool under the I/M System Information. When the HO2S test displays a YES status, indicating that the heated oxygen sensor system diagnostic is completed, check for a DTC P2238 in the Last Test Failed screen of the scan tool. If there is no DTC P2238 displayed the HO2S diagnostic has run and passed, indicating that no malfunction was present this time. The DTCs MUST be cleared in order to view the Current Status of the system diagnostics being performed. Do not forget that the I/M System Information tests only indicate that the test has run, not whether the test passed or failed. The Last Test Failed screen must be checked for related DTCs in order to determine the outcome of the diagnostic test involved.
-
If there is a short to ground or an open in the HO2S input circuit the scan tool can display HO2S 1 4.99 volts. This is a default value and not the actual sensor input circuit voltage.
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If there is a short or an open in the HO2S low reference circuit the scan tool can display HO2S 1 4.99 volts. This is a default value and not the actual sensor input circuit voltage.
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Operating the vehicle in Check Mode enhances the diagnostic capabilities of the PCM. The catalytic converter diagnostic can be monitored on the scan tool under the I/M System Information selection. When the Catalyst test displays a YES status, indicating that the catalytic converter system diagnostic is completed, check for DTC P0420 in the Last Test Failed screen of the scan tool. If there is no DTC P0420 displayed, the catalytic converter diagnostic has run and passed, indicating that no malfunction was present this time. The DTCs MUST be cleared in order to view the Current Status of the system diagnostics being performed. Do not forget that the I/M System Information tests only indicate that the test has run, not whether the test passed or failed. The Last Test Failed screen must be checked for related DTCs in order to determine the outcome of the diagnostic test involved.
Step | Action | Values | Yes | No | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics Connector End View Reference: Powertrain Control Module Connector End Views or Engine Controls Connector End Views | ||||||||||||
Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | ||||||||||
Did DTC P2238 set? | -- | Go to Step 3 | Go to Diagnostic Aids | |||||||||
3 |
Was a repair necessary? | -- | Go to Step 11 | Go to Step 4 | ||||||||
4 |
Is the resistance of the sensor within the specified range? | 1.2-3.4 ohms at 20°C (68°F | Go to Step 5 | Go to Step 9 | ||||||||
Is the voltage within the specified value? | 3.4-3.5 V | Go to Step 6 | Go to Step 7 | |||||||||
Is the voltage within the specified value? | 2.9-3.1 V | Go to Step 9 | Go to Step 8 | |||||||||
7 |
Did you find and correct a condition? | -- | Go to Step 11 | Go to Step 10 | ||||||||
8 |
Did you find and correct a condition? | -- | Go to Step 11 | Go to Step 10 | ||||||||
9 | Replace the HO2S 1. Refer to Heated Oxygen Sensor 1 Replacement . Did you complete the replacement? | -- | Go to Step 11 | -- | ||||||||
10 | Replace the PCM. Refer to Control Module References for replacement, setup, and programming. Did you complete the replacement? | -- | Go to Step 11 | -- | ||||||||
11 |
Did the DTC run and pass? | -- | Go to Step 12 | Go to Step 2 | ||||||||
Does DTC P0420 run and pass? | -- | Go to Step 13 | Go to DTC P0420 | |||||||||
13 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | -- | System OK | |||||||||
