For 1990-2009 cars

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 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 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 will be low, and the lambda value will be low, or less than 1. The ECM uses this information to maintain the correct air/fuel ratio.

### DTC Descriptors

This diagnostic procedure supports the following DTCs:

• | DTC P2626 HO2S Pumping Current Trim Circuit Bank 1 Sensor 1

• | DTC P2629 HO2S Pumping Current Trim Circuit Bank 2 Sensor 1

### Conditions for Running the DTC

• | Before the ECM can report DTC P2626 or P2629 failed, DTCs P0101, P0121, P0122, P0123, P0221, P0222, P0223, P0336, and P0338 must run and pass.

• | The engine is running.

• | The ignition 1 voltage is between 10.7-18.0 volts.

• | The fuel system is in fuel shut-off.

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

• | The heated oxygen sensors are at operating temperature.

• | DTC P2626 and P2629 runs continuously once the above conditions are met for 4 seconds.

### Conditions for Setting the DTC

The ECM internal HO2S voltage is more than 4.81 volts.

### Action Taken When the DTC Sets

• | The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.

• | The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

### Conditions for Clearing the MIL/DTC

• | The control module turns OFF the malfunction indicator lamp (MIL) after 4 consecutive ignition cycles that the diagnostic runs and does not fail.

• | A current DTC, last test failed, clears when the diagnostic runs and passes.

• | A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.

• | Clear the MIL and the DTC with a scan tool.

### Diagnostic Aids

• | The front wide band sensors do not toggle or switch like a switching HO2S. The front HO2S signals will be relatively stable for an idling engine.

• | Use the J 35616-A/BT-8637 Connector Test Adapter Kit for any test that requires probing the ECM harness connector or a component harness connector.

• | The lower connector of the ECM is connector C1 and the upper connector of the ECM is connector C2. Refer to Front of Vehicle/Engine Compartment Component Views.

• | For an intermittent condition, refer to Intermittent Conditions.

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

#### HO2S Voltages

HO2S Circuit | Voltage
--- | ---

• | Ignition ON, Engine OFF

• | HO2S Disconnected

Heater Control | 4.6-5.0 V
Heater Supply Voltage | B+
Reference Voltage | 2.6-3.1 V
Low Reference | 2.2-2.7 V
Pump Current | Less than 0.5 V
Input Pump Current | Less than 0.5 V

### Test Description

The numbers below refer to the step numbers on the diagnostic table.

1. This step determines if the condition exists. The HO2S lambda parameter should react immediately to the changes in throttle position when performing this test.

2. This step determines if there is a condition with the pumping current circuit. Connecting a jumper wire between the reference voltage and the low reference circuits causes the ECM to command the pumping current and the input pumping current circuits.

Step | Action | Values | Yes | No
--- | --- | --- | --- | ---
Schematic Reference: Engine Controls Schematics Connector End View Reference: Component Connector End Views
1 | Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | Go to Diagnostic System Check - Vehicle
2 | Note: DTC P2626 is for Bank 1 Sensor 1. DTC P2629 is for Bank 2 Sensor 1.

1. Start the engine.
2. Allow the engine to reach operating temperature.
3. Cycle the throttle from idle to wide open throttle 3 times within 5 seconds.
4. Observe the affected HO2S lambda value with a scan tool.

Does the affected HO2S lambda value react immediately to the above action?

--

Go to Step 4

Go to Step 3

3 |

1. Observe the Freeze Frame and/or the Failure records data for this DTC.
2. Turn the ignition OFF for 30 seconds.
3. Start the engine.
4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame and/or the Failure records data.

Does the DTC fail this ignition cycle?

--

Go to Step 4

Go to Diagnostic Aids

4 | Is DTC P0131, P0132, P0151, or P0152 also set? | -- | Go to Diagnostic Trouble Code (DTC) List - Vehicle | Go to Step 5
5 |

1. Turn OFF the ignition.
2. Disconnect the appropriate heated oxygen sensor (HO2S).
3. Turn the ignition switch to ON position, with the engine OFF.
4. Connect a 3-amp fused jumper wire between the reference voltage circuit and the low reference circuit of the HO2S.
5. Measure the voltage between the pump current circuit and a good ground.

Is the voltage more than the specified value?

1.0 V

Go to Step 7

Go to Step 6

6 | Test the pump current circuit of the HO2S for an open. Refer to Circuit Testing and Wiring Repairs. Did you find and correct the condition? | -- | Go to Step 11 | Go to Step 8
7 | Test for an intermittent and for a poor connection at the appropriate HO2S. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs. Did you find and correct the condition? | -- | Go to Step 11 | Go to Step 9
8 | Test for an intermittent and for a poor connection at the engine control module (ECM). Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs. Did you find and correct the condition? | -- | Go to Step 11 | Go to Step 10
9 | Replace the HO2S. Refer to the appropriate procedure:

• | Heated Oxygen Sensor Replacement - Bank 1 Sensor 1

• | Heated Oxygen Sensor Replacement - Bank 2 Sensor 1

Did you complete the replacement?

--

Go to Step 11

--

10 | Replace the ECM. Refer to Control Module References for replacement, setup, and programming. Did you complete the replacement? | -- | Go to Step 11 | --
11 |

1. Clear the DTCs with a scan tool.
2. Turn OFF the ignition for 30 seconds.
3. Start the engine.
4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.

Did the DTC fail this ignition?

--

Go to Step 2

Go to Step 12

12 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | Go to Diagnostic Trouble Code (DTC) List - Vehicle | System OK