BI-Fuel/Alternative Fuels

CIRCUIT DESCRIPTION
The Heated Oxygen Sensor (HO2S) is used in order to determine the oxygen content of the engine's exhaust. The oxygen content of the exhaust indicates when the engine is operating lean or rich. When the engine is operating lean, the exhaust will have more oxygen content. Once at operating temperature, the HO2S will produce a voltage in relation to the oxygen content of the exhaust. The HO2S requires an operating temperature of 360°C (600°F) to produce voltage. The HO2S will produce more voltage when the exhaust is rich and less voltage when the exhaust is lean. The HO2S operating voltage range is between 0.10 volts (100 mV) to 1 volt (1,000 mV).

The gasoline Control Module (VCM/PCM or ECM) supplies a bias (or reference) voltage to the HO2S. This bias voltage is around 450 mV. The Alternative Fuels ECM monitors the bias voltage as well as the voltage produced by the HO2S.

During normal Closed Loop fuel control operation, the Alternative Fuels ECM will add fuel (enriches the mixture) when the HO2S indicates a lean exhaust content. When the HO2S indicates a rich exhaust content, the Alternative Fuels ECM will subtract fuel (leans-out the mixture). This oscillation above and below the bias voltage (sometimes referred to as activity or switching) can be monitored with the HO2S signal voltage.

The oxygen sensor contains a heater. The heater is necessary in order to quickly warm the sensor to operating temperature. The heater will also maintain operating sensor temperature during extended idle conditions.

This DTC is used to indicate an HO2S with in-active signal voltage.

CONDITIONS FOR RUNNING THE DTC
^ The engine is operating on alternative fuel.
^ The engine speed is more than 400 RPM.
^ The engine has been operating for at least 4 minutes.
^ The Alternative Fuels ECM determines the HO2S has been at operating temperature for at least 30 seconds. Operating temperature is indicated when engine coolant temperature is more than 40°C (104°F) AND desired gas flow is greater than 0.3 grams per second for 30 seconds.

CONDITIONS FOR SETTING THE DTC
The Alternative Fuels ECM monitors an O2S signal voltage stuck between 0.347 V and 0.550 V (in-active) for 9 seconds continuously.

or

The Alternative Fuels ECM monitors an O2S signal voltage between 0.00 V and 1.0 V that has not performed a Rich/Lean switch for 15 seconds continuously.

ACTION TAKEN WHEN THE DTC SETS
The Alternative Fuels ECM will control fuel trim based upon the Bank 2 Sensor 1 signal. If a Bank 2 Sensor 1 DTC sets, the Alternative Fuels ECM will operate in Open Loop fuel control.
^ A first failure of this DTC will NOT illuminate the MIL and will store as Last Test Failed but not as History.
^ The Alternative Fuels ECM will illuminate the MIL and store the DTC as History after 2 consecutive drive trips that the diagnostic runs and fails.
^ The Alternative Fuels ECM will record operating conditions at the time the DTC sets. This information will be stored as Freeze Frame data.

CONDITIONS FOR CLEARING THE MIL/DTC
^ The Last Test Failed status will clear when the DTC runs and passes.
^ The Alternative Fuels ECM will turn OFF the MIL after 3 consecutive drive trips that the DTC runs and passes.
^ The History status will clear after 40 consecutive WARM-UP cycles with NO failures of ANY DTC.
^ All DTC Information can be cleared using a scan tool.
^ Interruption of Control Module (AF ECM/VCM/PCM or ECM) power or ground MAY clear DTC Information. Clearing DTC Information with this method is in-consistent and should not be performed.

DIAGNOSTIC AIDS

Intermittent Condition
A fault not present indicates the condition that caused the DTC to set is intermittent and not currently present. Refer to the Intermittent Conditions diagnostic information located in Symptoms - Computers and Control Systems. If any additional DTCs were stored proceed to the applicable DTC table in the order stated in Diagnostic System Check - Alternative Fuels (Computers and Control Systems). Initial Inspection and Diagnostic Overview Intermittent Conditions

TEST DESCRIPTION

Steps 1-6:

Steps 7-13:

Steps 14-19:

Steps 20-23:

The numbers below refer to the step numbers on the diagnostic table.
3. This step determines if proper sensor activity is present. When in Closed Loop fuel control, the HO2S voltage should rapidly vary between more than and less than the bias voltage.
7. This step determines if the gasoline Control Module and the High and Low circuits between the Control Module and the HO2S connector are operating properly.
10. This step determines if the HO2S heater circuit operates correctly up to the HO2S connector.
11. This step determines if the proper circuit resistance exists between the HO2S Low circuit and Control Module ground.
16. This step determines if the proper circuit resistance exists between the HO2S Low circuit and Control Module ground with a COLD sensor. A loose HO2S or faulty thread to exhaust electrical contact causes higher resistance when the HO2S is cold. Although 500 ohms is allowed the typical resistance should be less than 50 ohms.