Circuit Description
Heated oxygen sensors (HO2S) are used for fuel control and post catalyst monitoring. Each HO2S compares the oxygen content of the surrounding air with the oxygen content of the exhaust stream. When the vehicle is first started, the powertrain control module (PCM) operates in an Open Loop mode, ignoring the HO2S signal voltage when calculating the air-to-fuel ratio. The PCM circuitry that monitors the HO2S, generates a reference, or bias, voltage of 450 mV when the sensor is cold, high resistance. Once the HO2S warms up, the HO2S generates a voltage within a range of 0-1000 mV, depending on the exhaust gas oxygen content. High HO2S voltage output indicates a rich fuel mixture. Low HO2S voltage output indicates a lean mixture. Once fueling goes Closed Loop, the HO2S voltage will fluctuate above and below the bias voltage. A heating element inside the HO2S reduces the time required for the sensor to reach operating temperature, and provide an accurate voltage signal.
This DTC is designed to detect an HO2S voltage that remains at a high voltage for more than a specified number of seconds during the test conditions.
Conditions for Running the DTC
Rich Test Enable
| • | DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0200, P0300, P0351-P0358, P0400, P0401, P0404, P0405, P0410, P0440, P0442, P0443, P0446, P0449, P0452, P0453, P1120, P1125, P1220, P1221, P1258, P1404, P1441, P1514, P1515, P1516, P1517, or P1518 are not set. |
| • | The secondary air injection (AIR) and the exhaust gas recirculation (EGR) diagnostics are not active. |
| • | The ignition voltage is more than 9 volts. |
| • | The fuel system is operating in Closed Loop. |
| • | The accelerator pedal position (APP) indicated angle is between 3-70 percent. |
| • | The fuel level is more than 10 percent. |
or
Decel Fuel Cut-off (DFCO) Test Enable
| • | DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0200, P0300, P0351-P0358, P0400, P0401, P0404, P0405, P0410, P0440, P0442, P0443, P0446, P0449, P0452, P0453, P1120, P1125, P1220, P1221, P1258, P1404, P1441, P1514, P1515, P1516, P1517 or P1518 are not set. |
| • | The AIR and the EGR diagnostics are not active. |
| • | The ignition voltage is more than 9 volts. |
| • | The fuel system is operating in Closed Loop. |
| • | The fuel level is more than 10 percent. |
| • | The decel fuel cut-off (DFCO) mode is enabled for more than 2 seconds. |
Conditions for Setting the DTC
Rich Test
| • | The HO2S signal voltage remains above 775 mV. |
| • | The criteria 1 conditions are present for 155 seconds. |
or
DFCO Test
| • | The HO2S signal voltage remains above 540 mV for 4.5 seconds. |
| • | The criteria 2 conditions are present for 4.5 seconds during the DFCO mode. |
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. |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
This step tests for a shorted HO2S high signal circuit.
-
This step tests for an open HO2S low reference circuit.
-
Monitor the HO2S voltage of the opposite bank sensor. If the voltage activity of the opposite bank sensor is similar to the voltage activity of the suspect sensor, test for rich conditions that would affect both cylinder banks. An opposite bank sensor with normal HO2S voltage activity indicates the suspect HO2S is defective or a rich condition exists only on the suspect HO2S cylinder bank.
Step | Action | Values | Yes | No | ||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics | ||||||||||||||||||||
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | |||||||||||||||||
2 |
Is the HO2S voltage fixed at more than the value specified? | 976 mV | Go to Step 4 | Go to Step 3 | ||||||||||||||||
3 |
Did the DTC fail this ignition? | -- | Go to Step 4 | Go to Intermittent Conditions | ||||||||||||||||
Does the HO2S voltage measure within the specified range? | 351-551 mV | Go to Step 5 | Go to Step 6 | |||||||||||||||||
Does the voltage measure less than the specified value? | 20 mV | Go to Step 8 | Go to Step 7 | |||||||||||||||||
6 | Test the HO2S high signal circuit for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 10 | ||||||||||||||||
7 | Test the HO2S low reference circuit for an open or high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 10 | ||||||||||||||||
Notice: Contamination of the oxygen sensor can result from the use of an inappropriate RTV sealant (not oxygen sensor safe) or excessive engine coolant or oil consumption. Remove the HO2S and visually inspect the portion of the sensor exposed to the exhaust stream in order to check for contamination. If contaminated, the portion of the sensor exposed to the exhaust stream will have a white powdery coating. Silicon contamination causes a high but false HO2S signal voltage (rich exhaust indication). The control module will then reduce the amount of fuel delivered to the engine, causing a severe driveability problem. Eliminate the source of contamination before replacing the oxygen sensor.
Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 9 | |||||||||||||||||
9 | Inspect for poor connections at the harness connector of the affected 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 13 | Go to Step 11 | ||||||||||||||||
10 | 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 13 | Go to Step 12 | ||||||||||||||||
11 |
Important: Before replacing a contaminated HO2S determine and repair the cause of the contamination. Replace the affected HO2S. Refer to Heated Oxygen Sensor Replacement - Bank 1 Sensor 1 or Heated Oxygen Sensor Replacement - Bank 2 Sensor 1 . Did you complete the replacement? | -- | Go to Step 13 | -- | ||||||||||||||||
12 | Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | -- | Go to Step 13 | -- | ||||||||||||||||
13 |
Did the DTC run and pass? | -- | Go to Step 14 | Go to Step 2 | ||||||||||||||||
14 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | -- | System OK | |||||||||||||||||
