Circuit Description
The powertrain control module (PCM) supplies a voltage of about 450 mV between the HO2S high and low signal circuits. The oxygen sensor 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 PCM monitors and stores the heated oxygen sensor (HO2S) voltage information. The PCM evaluates the HO2S voltage samples in order to determine the amount of time the HO2S voltage was out of range. The PCM 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 PCM monitors the HO2S voltage for being fixed above a predetermined voltage. If the PCM detects the voltage is above a predetermined voltage, a DTC sets.
DTC Descriptors
This diagnostic procedure supports the following DTCs.
| • | DTC P0138 HO2S Circuit High Voltage Bank 1 Sensor 2 |
| • | DTC P0158 HO2S Circuit High Voltage Bank 2 Sensor 2 |
Conditions for Running the DTC
| • | DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0121, P0122, P0123, P0125, P0128, P0200, P0300, P0443, P0496, P1111, P1112, P1114, P1115, P1121, or P1122 are not set. |
| • | The ignition 1 voltage is between 10-18 volts. |
| • | The fuel level is more than 10 percent. |
| • | The loop status is CLOSED. |
| • | Intrusive tests are not in progress. |
| • | DTC P0138 and P0158 run continuously when the above conditions are met. |
Rich Test Enable
| • | The air fuel ratio is between 14.5:1 and 14.7:1. |
| • | The throttle position (TP) is between 3-70 percent. |
| • | The above conditions are met for at least 2 seconds. |
Decel Fuel Cut-Off Test Enable
| • | Decel fuel cut-off is active for 2 seconds. |
| • | The engine has been running for at least 30 seconds. |
Conditions for Setting the DTC
Rich Test
The HO2S voltage is more than 950 mV for 200 seconds.
Decel Fuel Cut-Off Test
The HO2S voltage is more than 480 mV for 5 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. |
Diagnostic Aids
Important:
• Before you service the PCM, remove any debris from the PCM connector surfaces.
Inspect the PCM connector gaskets when you diagnose or replace the PCM. Ensure that
the gaskets are installed correctly. The gaskets prevent contaminant intrusion into
the PCM. • For any test that requires probing the PCM or probing the component harness
connectors, use the J 35616
Connector
Test Adapter Kit. Using this kit prevents any damage to the harness connector terminals.
Refer to
Using Connector Test Adapters
in Wiring
Systems.
Inspect the following components for the following conditions:
| • | The HO2S electrical connections--Inspect the HO2S electrical connections for evidence of water intrusion. Water present in the connector causes the B+ supply to the heater to bleed over to the signal circuit. |
| • | The fuel pressure--The system goes rich if the pressure is too high. The PCM compensates for some increase. If the fuel pressure is too high, a DTC may set. Refer to Fuel System Diagnosis . |
| • | Rich injectors--Perform the Injector Balance Test. Refer to Fuel Injector Balance Test with Tech 2 or Fuel Injector Balance Test with Special Tool . |
| • | Leaking injectors--Refer to Fuel System Diagnosis . |
| • | The evaporative emissions (EVAP) canister purge--Inspect for fuel saturation. If the canister is full of fuel, inspect the canister control and inspect the hoses. Refer to Evaporative Emission Control System Description . |
| • | The MAF sensor--Disconnect the MAF sensor and see if the rich condition is corrected. If the condition is corrected, inspect for proper installation. If the sensor is properly installed, replace the MAF sensor. If the MAF sensor is installed backwards, the system goes rich. The plastic portion of the sensor has arrows that indicate the proper air flow direction. The arrows must point toward the engine. |
| • | The oxygen supply--An oxygen supply inside the HO2S is necessary for proper operation. The HO2S wires provide the supply of oxygen. Inspect the HO2S wires and connections for breaks or for contamination. Refer to Heated Oxygen Sensor Wiring Repairs in Wiring Systems. |
| • | The TP sensor--An intermittent TP sensor output causes the system to go rich, due to a false indication of engine acceleration. |
For an intermittent condition, refer to Intermittent Conditions .
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
If the voltage is above the specified valve, the conditions is present.
-
If the voltage remains high, the HO2S high signal circuit is shorted to a voltage. If the voltage goes low, a rich condition exists.
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-Engine Controls? | -- | Go to Step 2 | |||||||||||||||
Is the HO2S voltage more than the specified value? | 930 mV | Go to Step 5 | Go to Step 3 | |||||||||||||||
3 |
Is the HO2S voltage within the specified range? | 350-550 mV | Go to DTC P0140 or P0160 | Go to Step 4 | ||||||||||||||
4 |
Does the DTC fail this ignition? | -- | Go to Step 5 | Go to Diagnostic Aids | ||||||||||||||
Is the HO2S voltage within the specified range? | 350-550 mV | Go to Step 6 | Go to Step 7 | |||||||||||||||
6 |
Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 8 | ||||||||||||||
7 |
Notice: A short to voltage on the heated oxygen sensor (HO2S) high signal circuit may damage the HO2S. Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 9 | ||||||||||||||
8 | Inspect for poor connections at the harness connector of 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 12 | Go to Step 10 | ||||||||||||||
9 | Inspect for poor connections at the harness connector of the PCM. 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 12 | Go to Step 11 | ||||||||||||||
10 | Replace the affected HO2S. Refer to Heated Oxygen Sensor Replacement - Bank 1 Sensor 2 or Heated Oxygen Sensor Replacement - Bank 2 Sensor 2 . Did you complete the replacement? | -- | Go to Step 12 | -- | ||||||||||||||
11 | Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | -- | Go to Step 12 | -- | ||||||||||||||
12 |
Does the DTC run and pass? | -- | Go to Step 13 | Go to Step 2 | ||||||||||||||
13 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | -- | System OK | |||||||||||||||
