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 engine control module (ECM) operates in an open loop mode, ignoring the HO2S signal voltage when calculating the air-to-fuel ratio. The ECM supplies the HO2S with a reference, or bias, voltage of about 450 mV. The HO2S generates a voltage within a range of 0-1,000 mV that fluctuates above and below bias voltage once in closed loop. High HO2S voltage output indicates a rich fuel mixture; low HO2S voltage output indicates a lean mixture. Heating elements inside the HO2S minimize the time required for the sensors to reach operating temperature, and to provide an accurate voltage signal. Fuel Trim Biasing is used by the ECM to keep the post catalyst HO2S voltage as close to 600 mV as possible. This allows optimal catalyst efficiency under light load conditions, such as at idle or a steady cruise. The ECM constantly monitors how long the Fuel Trim Bias is commanded lean or rich. If the ECM detects that the Fuel Trim Bias is commanded lean for longer than a calibrated amount, DTCs P2096, or P2098 will set.
Each HO2S has the following circuits:
| • | The HO2S high signal circuit |
| • | The HO2S low signal circuit |
| • | The HO2S heater ignition 1 voltage circuit |
| • | The HO2S heater low control circuit |
Conditions for Running the DTC
| • | DTCs P0030, P0031, P0032, P0036, P0037, P0038, P0050, P0051, P0052, P0056, P0057, P0058, P0101, P0102, P0103, P0116, P0117, P0118, P0125, P0128, P0135, P0141, P0155, P0161, P0171, P0172, P0174, P0175, P0300, P0301-P0306, P0313, P0341, P0342, P0343, P0420, P0430, P0443, P0444, or P0445 are not set. |
| • | The loop status parameter is closed. |
Conditions for Setting the DTC
The ECM detects that the affected HO2S 1 fuel trim bias is commanded lean for longer than 1.3 seconds, within a 200 second monitoring period.
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
| • | The most likely cause for this DTC is a deteriorated or contaminated HO2S 1. |
| • | Depending on the state of the HO2S deterioration, this code may not reset or may be very difficult to reset. |
| • | If the HO2S deterioration is significant enough, other HO2S DTCs may set or be present in concurrence with this DTC. |
| • | Attempt to compare the activity of both the affected bank HO2S 1 and HO2S 2 to the known good bank using the live plot feature of the scan tool. Operate the vehicle under various load and vehicle/engine speed conditions. Look for any indication of improper operation or contamination of the affected bank HO2S 1 or HO2S 2. |
| • | If an intermittent condition exists, refer to Intermittent Conditions . |
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics Connector End View Reference: Engine Controls Connector End Views or Engine Control Module Connector End Views | ||||
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | |
2 |
Important: This code may be set due to a slow or unresponsive HO2S 1 or HO2S 2.
Does the voltage fluctuate above and below the specified range? | 400-597 mV | Go to Step 3 | Go to Step 5 DTC P0134 or P0154 |
3 |
Important: This code may be set due to a slow or unresponsive HO2S 1 or HO2S 2.
Does the voltage respond instantly to the above action? | -- | Go to Diagnostic Aids | Go to Step 4 DTC P0140 or P0160 |
