• | 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. |
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 |
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 | 1,000 mV |
Low Reference | -- | 400-415 mV | 1,000 mV |
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 |
• | The engine airflow is greater than 6 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 10 seconds. |
• | The engine is in power enrichment (PE) mode. |
• | The DTCs run continuously when the above conditions are met for 2 seconds. |
The engine control module (ECM) detects that the HO2S voltage is less than 350 mV and the air/fuel ratio is less than 13.5:1 during PE mode.
DTCs P1137 and P1166 are type B DTCs.
DTCs P1137 and P1166 are type B DTCs.
• | Circuit Testing |
• | Wiring Repairs |
Powertrain Diagnostic Trouble Code (DTC) Type Definitions
Control Module References for scan tool information
⇒ | If less than the specified range, test the signal circuit for a short to ground. If the circuit tests normal, replace the ECM. |
• | Engine vacuum leaks |
• | Exhaust leaks near the HO2S |
• | Water intrusion in the HO2S harness connector |
• | Low fuel system pressure--Refer to Fuel System Diagnosis. |
• | Lean fuel injectors--Refer to Fuel Injector Balance Test with Special Tool. |
• | Fuel that is contaminated--Refer to Alcohol/Contaminants-in-Fuel Diagnosis. |
• | Contaminated HO2S--Silicon |
⇒ | If you find any of the above conditions, repair as necessary. |
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
• | Control Module References for engine control module replacement, setup, and programming |