| Table 1: | HO2S Voltages |
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 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 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 more 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 PCM uses this information to maintain the correct air/fuel ratio. If the PCM detects that the low reference circuit voltage is less than a predetermined voltage, this DTC sets.
DTC Descriptors
This diagnostic procedure supports the following DTCs:
| • | DTC P2252 HO2S Low Reference Circuit Low Voltage Bank 1 Sensor 1 |
| • | DTC P2255 HO2S Low Reference Circuit Low Voltage Bank 2 Sensor 1 |
Conditions for Running the DTC
| • | The engine is operating for more than 85 seconds. |
| • | The HO2S heater is commanded ON. |
| • | DTC P2252 and P2255 run continuously once the above conditions have been met. |
Conditions for Setting the DTC
| • | The HO2S sensing cell voltage is 0.3 volt or less, and the HO2S pumping cell voltage is 1 volt or more. |
| • | The above condition is met for less than 1 second. |
Action Taken When the DTC Sets
| • | The PCM illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails. |
| • | The PCM records the operating conditions at the time the diagnostic fails. The PCM stores this information in the Freeze Frame and/or Failure Records. |
Conditions for Clearing the MIL/DTC
| • | The PCM turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail. |
| • | A last test failed, or current DTC, clears when the diagnostic runs and does not fail. |
| • | A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic. |
| • | Use a scan tool in order to clear the MIL and the DTC. |
Diagnostic Aids
| • | Use the J-35616 Connector Test Adapter Kit for any test that requires probing the PCM harness connector or a component harness connector. |
| • | The Loop Status for the respective bank will default to Open when the DTC is current. |
| • | The wide band sensors do not toggle or switch like a switching HO2S. The HO2S signals will be relatively stable for an idling engine. |
| • | For an intermittent condition, refer to Intermittent Conditions . |
| • | The following table illustrates the typical voltages for the HO2S circuits: |
| |||||
|---|---|---|---|---|---|
HO2S Circuit | Voltage | ||||
Heater Control | Less than 0.5 V | ||||
Heater Supply Voltage | B+ | ||||
Reference Voltage | 3.3-3.8 V | ||||
Low Reference | 5.9-6.4 V | ||||
Pump Current | 4.8-5.3 V | ||||
Input Pump Current | 3.3-3.8 V | ||||
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
This step determines whether a condition currently exists. If the lambda value fluctuates near 1.00 and Loop Status is Closed, the HO2S is operating correctly.
-
This step tests for a condition in the low reference circuit. Test for a short to ground, or a wire to wire short to the HO2S reference ground circuit, if the voltage measures less than 1 volt.
-
Inspect the HO2S connector for water intrusion, corrosion, and bent or damaged terminals.
-
Inspect the PCM connectors for water intrusion, corrosion, and bent or damaged terminals.
-
After replacing the PCM, a new minimum throttle position and idle speed must be established.
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 | ||||
1 | Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | |
|
Important: DTC P2252 is for bank 1 sensor 1 - rear and DTC P2255 is for bank 2 sensor 1 - front.
Does the scan tool display Closed Loop? | -- | Go to Step 3 | Go to Step 4 | |
3 |
Did the DTC fail this ignition? | -- | Go to Step 4 | Go to Diagnostic Aids |
Is the voltage less than the specified value? | 1 V | Go to Step 5 | Go to Step 6 | |
5 | Test the low reference circuit of the HO2S for a short to ground, or a short to the reference ground circuit of the HO2S. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 10 | Go to Step 7 |
Test for shorted terminals and for poor connections at the HO2S sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | -- | Go to Step 10 | Go to Step 8 | |
Test for shorted terminals and for poor connections at the powertrain control module (PCM). Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | -- | Go to Step 10 | Go to Step 9 | |
8 | Replace the HO2S sensor. Refer to Heated Oxygen Sensor Replacement - Bank 1 Sensor 1 or Heated Oxygen Sensor Replacement - Bank 2 Sensor 1 . Did you complete the replacement? | -- | Go to Step 10 | -- |
Did you complete the replacement? | -- | Go to Step 10 | -- | |
10 |
Did the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 11 |
11 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | System OK | |
