Circuit Description
The engine control module (ECM) supplies a voltage near 450 mV between the heated oxygen sensor (HO2S) high signal circuit and the low reference circuit. The HO2S varies the voltage over a range from about 1,000 mV when the exhaust is rich, down through about 10 mV when the exhaust is lean.
The ECM monitors and stores the HO2S voltage information. The ECM evaluates the HO2S voltage samples in order to determine the amount of time that the HO2S voltage was out of range. The ECM compares the stored HO2S voltage samples taken within each sample period and determines if the majority of the samples are out of the operating range.
The HO2S utilizes the following circuits:
| • | A signal circuit |
| • | A low reference circuit |
| • | An ignition 1 voltage circuit |
| • | A heater control circuit |
The ECM monitors the HO2S voltage for being fixed below a predetermined voltage or within the bias voltage range. If the ECM detects the voltage is too low or is within the bias voltage range, the DTC sets.
DTC Descriptor
This diagnostic procedure supports the following DTCs:
| • | DTC P0137 HO2S Circuit Low Voltage Bank 1 Sensor 2 |
| • | DTC P0157 HO2S Circuit Low Voltage Bank 2 Sensor 2 |
Conditions for Running the DTC
Closed Loop Test
| • | The engine is running. |
| • | The DTCs run continuously once the above condition are met for 10 milliseconds. |
Decel Fuel Cut-Off (DFCO) Test
| • | The H02S test is ran when the following conditions are met during DFCO mode: |
| • | The ignition 1 voltage is more 10 volts. |
| • | The fuel system is in closed loop. |
| • | The mass air flow is more than 40 g/s during decel fuel cut-off. |
| • | The engine speed is less than 6000 RPM. |
| • | The DTCs run continuously once the above conditions are met 10 milliseconds. |
Conditions for Setting the DTC
Closed Loop Test
| • | The ECM detects that the HO2S voltage is less than 100 mV. |
| • | The condition exists for more than 20 seconds. |
Decel Fuel Cut-Off (DFCO) Test
| • | The ECM detects that the HO2S voltage is between 352-499 mV. |
| • | The condition exists for more than 20 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 3 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. |
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 - Engine Controls? | -- | Go to Step 2 | |||||||||||
2 |
Does the voltage fluctuate above and below the specified range? | 352-499 mV | Go to Step 3 | Go to Step 4 | ||||||||||
3 |
Did the DTC fail this ignition? | -- | Go to Step 4 | Go to Intermittent Conditions | ||||||||||
4 |
Is the voltage within the specified range? | 350-550 mV | Go to Step 5 | Go to Step 7 | ||||||||||
5 |
Is the voltage less than the specified value? | 20 mV | Go to Step 9 | Go to Step 6 | ||||||||||
6 |
Is the voltage less than the specified value? | 20 mV | Go to Step 8 | Go to Step 7 | ||||||||||
7 | Test the HO2S signal circuit for one of the following conditions:
Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 14 | Go to Step 11 | ||||||||||
8 | Test the HO2S low reference circuit for one of the following conditions:
Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 14 | Go to Step 11 | |||||||||||
9 | Test or inspect for the following conditions:
Did you find and correct the condition? | -- | Go to Step 14 | Go to Step 10 | ||||||||||
10 | Test for shorted terminals and poor connections at the HO2S. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 14 | Go to Step 12 | ||||||||||
11 | Test for shorted terminals and poor connections at the engine control module (ECM). Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 14 | Go to Step 13 | ||||||||||
12 | Replace the appropriate HO2S. Did you complete the replacement? | -- | Go to Step 14 | -- | ||||||||||
13 | Replace the ECM. Refer to Engine Control Module Replacement . Did you complete the replacement? | -- | Go to Step 14 | -- | ||||||||||
14 |
Did the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 15 | ||||||||||
15 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | System OK | |||||||||||
