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 DTC:
DTC P0137 HO2S Circuit Low Voltage Sensor 2
Conditions for Running the DTC
Closed Loop Test
| • | DTCs P0107, P0108, P0117, P0118, P0122, P0123, P0335, P0336, P0337, P0341, P0342, P0400, P0404, P0405, P0406, P1320, and P1321 are not set. |
| • | The engine is running. |
| • | The engine speed is less than 6,000 RPM. |
| • | The DTC runs continuously once the above conditions are met. |
Decel Fuel Cut-Off (DFCO) Test
| • | The H02S test is ran when the following conditions are met during DFCO mode: |
| - | DTCs P0107, P0108, and P0141 are not set. |
| - | The ignition 1 voltage is more 10 volts. |
| - | The engine speed is less than 6000 RPM. |
| - | The fuel system is in closed loop. |
| • | The DTC runs continuously once the above conditions are met. |
Conditions for Setting the DTC
Closed Loop Test
| • | The ECM detects that the HO2S voltage is less than 70 mV. |
| • | The condition exists for more than 40 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 10 seconds. |
Action Taken When the DTC Sets
| • | The malfunction indicator lamp (MIL) will illuminate after 3 consecutive trips with a fail. |
| • | The ECM will record operating conditions at the time the diagnostic fail. This information will be stored in the Freeze Frame and Failure Records. |
| • | The coolant fan turns ON. |
Conditions for Clearing the MIL/DTC
| • | The MIL will turn OFF after 4 consecutive ignition cycles in which the diagnostic runs without a fault. |
| • | DTCs can be cleared by using the scan tool. |
| • | Disconnect the ECM battery feed for 10 seconds. |
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 HO2S. Refer to Heated Oxygen Sensor 2 Replacement . 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 | Are there any DTCs that have not been diagnosed? | -- | System OK | |||||||||||
