Diagnostic Instructions
| • | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. |
| • | Review Strategy Based Diagnosis for an overview of the diagnostic approach. |
| • | Diagnostic Procedure Instructions provides an overview of each diagnostic category. |
DTC Descriptor
DTC P1166: HO2S Circuit Low Voltage During Power Enrichment Sensor 2Diagnostic Fault Information
Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance |
|---|---|---|---|---|
HO2S Signal | P0131, P0137, P1137, P1166 | P0134, P0140 | P0132, P0138, P1138, P2297 | P0133 |
Low Reference | -- | P0134, P0140 | P0132, P0138, P1138, P2297 | P0133 |
Typical Scan Tool Data
Circuit | Short to Ground | Open | Short to Voltage |
|---|---|---|---|
Operating Conditions: Engine operating in Closed Loop. Parameter Normal Range: Fluctuates above and below 350-500 mV. | |||
HO2S 1 and 2 Signal | 0 mV | 400-415 mV | 1000 mV |
Low Reference | -- | 400-415 mV | 1000 mV |
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 engine 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 about 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 |
Conditions for Running the DTC
| • | DTCs P0106, P0107, P0108, P0117, P0118, P0122, P0123, P0171, P0172, P0201, P0202, P0203, P0204, P0300, P0336, P0337, P0351, P0352, P0402, P0404, P0405, P0406, P0443, P0502, P0506, P0507, and P1404 are not set. |
| • | The engine airflow is greater than 13.5 g/s. |
| • | The startup engine coolant temperature is greater than 60°C (140°F). |
| • | The ignition 1 voltage is greater than 10 volts. |
| • | The engine has been operating for 60 seconds. |
| • | The engine is in power enrichment (PE) mode. |
| • | The DTCs run continuously when the above conditions are met for 3 seconds. |
Conditions for Setting the DTC
The ECM detects that the HO2S voltage is less than 350 mV during power enrichment (PE) mode.
Action Taken when the DTC Sets
DTC P1166 is a Type B DTC.
Conditions for Clearing the MIL/DTC
DTC P1166 is a Type B DTC.
Reference Information
Schematic Reference
Electrical Information Reference
DTC Type Reference
Powertrain Diagnostic Trouble Code (DTC) Type Definitions
Scan Tool Reference
Control Module References for scan tool information
Circuit/System Verification
- Engine running, observe the scan tool heated oxygen sensor 2 (HO2S) voltage parameter. The reading should be between 350-550 mV.
- Operate the vehicle within the Conditions for Running the DTC to verify the DTC does not reset. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.
Circuit/System Testing
- Ignition OFF, disconnect the harness connector at the heated oxygen sensor 2 (HO2S).
- Ignition ON, verify the scan tool HO2S 2 parameter is between 350-500 mV.
- Verify none of the following conditions exist:
- If all circuits test normal, test or replace the HO2S sensor 2.
| ⇒ | If less than the specified range, test the signal circuit for a short to ground. If the circuit tests normal, replace the ECM. |
| • | Lean fuel injectors--Refer to Fuel Injector Balance Test with Special Tool . |
| • | Water intrusion in the HO2S harness connector |
| • | Low fuel system pressure--Refer to Fuel System Diagnosis . |
| • | Fuel that is contaminated--Refer to Alcohol/Contaminants-in-Fuel Diagnosis . |
| • | Exhaust leaks near the HO2S |
| • | Contaminated HO2S--Silicon |
| • | Engine vacuum leaks |
| ⇒ | If you find any of the above conditions, repair as necessary. |
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
Control Module References for ECM replacement, setup, and programming
