| 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 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 ECM uses this information to maintain the correct air/fuel ratio.
DTC Descriptors
This diagnostic procedure supports the following DTCs:
| • | DTC P2237 HO2S Pumping Current Control Circuit Bank 1 Sensor 1 |
| • | DTC P2240 HO2S Pumping Current Control Circuit Bank 2 Sensor 1 |
Conditions for Running the DTC
Conditions 1
| • | Before the ECM can report DTC P2237 or P2240 failed, DTC 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, and P0155 are not set. |
| • | The engine is operating in closed loop. |
| • | The ignition 1 voltage is between 10.7-18 volts. |
| • | The HO2S heater is at operating temperature. |
| • | The ECM is commanding the lambda more than 1.03 or less than 0.97. |
| • | More 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, DTC P0101, P0121, P0122, P0123, P0221, P0222, P0223, P0335, P0336, and P0338 must run and pass. |
| • | The ignition 1 voltage is between 10.7-18 volts. |
| • | The engine is operating in closed loop. |
| • | The HO2S heater is at operating temperature. |
| • | The ECM detects the internal HO2S signal voltage is between 1.48-1.52 volts. |
| • | The ECM is commanding the lambda rich and then lean periodically with a change of more than 2 percent. |
| • | DTC P2237 and P2240 run continuously once the above conditions are met for approximately 1.5 seconds. |
Conditions 3
| • | The ignition 1 voltage is between 10.7-18 volts. |
| • | The HO2S heater is at operating temperature. |
| • | The ECM is commanding decel fuel cut-off for more than 3 seconds. |
| • | DTC P2237 and P2240 run continuously once the above conditions are met for more than 2 seconds. |
Conditions for Setting the DTC
Conditions 1
| • | The ECM detects the internal HO2S signal voltage is between 1.48-1.52 volts while the desired lambda is above or below a threshold. |
| • | The above condition exists for more 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 more than 10 percent of the lambda value. |
| • | The above condition exists for more than 4 seconds. |
Conditions 3
| • | The ECM detects the internal HO2S signal voltage after a decel fuel shut-off is less than 1.7 volts. |
| • | The above condition exists for more than 4 seconds. |
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 Engine Controls Component Views . |
| • | For an intermittent condition, refer to Intermittent Conditions . |
| • | The following table illustrates the typical voltages for the HO2S circuits. |
HO2S Circuit | Voltage | ||||
|---|---|---|---|---|---|
| |||||
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.
-
This step determines if the condition exists. The HO2S lambda parameter should react immediately to the changes in throttle position when performing this test.
-
This step determines if there is a condition with the input pump current and pump 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: Engine 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 P2237 is for bank 1 sensor 1. DTC P2240 is for bank 2 sensor 1.
Does the affected HO2S lambda value react immediately to the above action? | -- | 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 more than the specified value? | 1 V | Go to Step 6 | Go to Step 5 | |
5 | Test the input pump current and 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 10 | Go to Step 7 |
6 | Test for an intermittent and for a poor connection at the HO2S. 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 |
7 | 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 10 | Go to Step 9 |
8 | Replace the HO2S. Refer to the appropriate procedure: Did you complete the replacement? | -- | Go to Step 10 | -- |
9 | Replace the ECM. Refer to Control Module References for replacement, setup, and programming. 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 | |
