Circuit Description
The heated oxygen sensors (HO2S) are used for fuel control and catalyst monitoring. Each HO2S compares the oxygen content of the surrounding air with the oxygen content of the exhaust stream. When the vehicle is started, the control module operates in an Open Loop mode, ignoring the HO2S signal voltage while calculating the air-to-fuel ratio. The control module supplies the HO2S with a reference, or bias, voltage of approximately 450 mV. While the engine runs, the HO2S heats up and begins to generate a voltage within a range of 0-1,000 mV. This voltage will fluctuate above and below the bias voltage. Once sufficient HO2S voltage fluctuation is observed by the control module, Closed Loop is entered. The control module uses the HO2S voltage to determine the air-to-fuel ratio. An HO2S voltage that increases above bias voltage toward 1,000 mV indicates a rich fuel mixture. An HO2S voltage that decreases below bias voltage toward 0 mV indicates a lean fuel mixture.
The heating elements inside each HO2S heat the sensor to bring the sensor up to operating conditions faster. This allows the system to enter Closed Loop earlier and the control module to calculate the air-to-fuel ratio sooner.
The HO2S utilizes the following circuits:
| • | A signal circuit |
| • | A low reference circuit |
| • | An ignition 1 voltage circuit |
| • | A heater control circuit |
If the ECM detects the HO2S 1 voltage signal is too low during Power Enrichment (PE) mode, this DTC sets.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P1171 HO2S Circuit Low Voltage During Power Enrichment Sensor 1
Conditions for Running the DTC
| • | DTCs P0106, P0107, P0108, P0117, P0118, P0122, P0123, P0171, P0172, P0201-P0204, P0300, P0336, P0337, P0351, P0352, P0401, P0402, P0404, P0405, P0406, P0441, P0443, P0488, P0502, P0506, P0507, and P01404 are not set. |
| • | The engine coolant temperature is more than 60°C (140°F). |
| • | The ignition 1 voltage is more than 10 volts. |
| • | The air fuel ratio is less than or equal to 13.5:1. |
| • | The engine is in Power Enrichment (PE) mode. |
| • | DTC P1171 runs continuously once the above conditions are met for 2 seconds. |
Conditions for Setting the DTC
The ECM detects that the HO2S 1 voltage is less than 350 mV for 11 seconds during Power Enrichment (PE) mode.
Action Taken When the DTC Sets
| • | The control module illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails. |
| • | The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Freeze Frame/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 Connect 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 | Observe the DTC Information with a scan tool. Is DTC P0131 or P0134 also set? | -- | Go to Step 3 | |||||||||||
3 |
Does the voltage remain below the specified value? | 350 mV | Go to Step 5 | Go to Step 4 | ||||||||||
4 |
Did the DTC fail this ignition? | -- | Go to Step 5 | Go to Intermittent Conditions | ||||||||||
5 |
Is the voltage within the specified range? | 350-550 mV | Go to Step 7 | Go to Step 6 | ||||||||||
6 | Test the HO2S 1 high signal circuit for a short to ground or a short to the HO2S 1 low reference circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 9 | ||||||||||
7 |
Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 8 | ||||||||||
8 | Test for an intermittent and poor connections at the harness connector of the HO2S 1 sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. | -- | Go to Step 12 | Go to Step 10 | ||||||||||
9 | Test for an intermittent and poor connection at the engine control module (ECM). Refer to Testing for Intermittent Conditions and Poor Connections and Repairing Connector Terminals in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 11 | ||||||||||
10 | Replace the O2S 1/HO2S 1. Refer to Oxygen Sensor Replacement . Did you complete the replacement? | -- | Go to Step 12 | -- | ||||||||||
11 | Replace the ECM. Refer to Engine Control Module Replacement . Did you complete the replacement? | -- | Go to Step 12 | -- | ||||||||||
12 |
Did the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 13 | ||||||||||
13 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | System OK | |||||||||||
