BI-Fuel/Alternative Fuels

Schematic:

CIRCUIT DESCRIPTION
The Oxygen Sensor (O2S) 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 O2S will produce a voltage in relation to the oxygen content of the exhaust. The O2S requires an operating temperature of 360°C (600°F) to produce voltage. The O2S will produce more voltage when the exhaust is rich and less voltage when the exhaust is lean. The O2S operating voltage range is around 0.1 volts (100 mV) to 1 volt (1000 mV).

The gasoline control module (VCM/PCM or ECM) supplies a bias (or reference) voltage to the O2S. This bias voltage is around 450 millivolts. The AF ECU monitors the bias voltage as well as the voltage produced by the O2S.

During normal Closed Loop fuel control operation the AF ECU will add fuel (enriches the mixture) when the O2S indicates a lean exhaust content. When the O2S indicates a rich exhaust content the AF ECU 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 O2S signal voltage.

This DTC is used to indicate an O2S with in-active signal voltage.

CONDITIONS FOR RUNNING THE DTC
^ The engine is operating on alternative fuel.
^ Engine speed is greater than 500 RPM.
^ The engine has been operating for at least 2 minutes.
^ The AF ECU determines the O2S has been at operating temperature for at least 2 minutes. The engine coolant temperature must be greater than 40°C (104°F) AND the calculated mass air flow must be above 6 grams per second for 2 minutes in order for the AF ECU to determine the O2S is at operating temperature.

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

OR

The AF ECU 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 AF ECU 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 AF ECU will illuminate the MIL and store the DTC as History after TWO consecutive drive trips that the diagnostic runs and fails.
^ The AF ECU 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 AF ECU 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 ECU/VCM/PCM or ECM) power or ground MAY clear DTC Information. Clearing DTC Information with this method is inconsistent and should not be performed.

DIAGNOSTIC AIDS
Fault Not Present
Fault Not Present indicates the condition that caused the DTC to set is intermittent and not currently present. Refer to 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 the Diagnostic System Check - Alternative Fuels (Computers and Control Systems). Intermittent Conditions

TEST DESCRIPTION

Steps 1-4:

Steps 5-10:

Steps 11-16:

The numbers below refer to the step numbers on the diagnostic table.
2. This step determines if proper sensor activity is present. When in Closed Loop fuel control the O2S voltage should rapidly swing above and below the bias voltage.
6. This step determines if the gasoline control module and the High and Low circuits between the control module and the O2S connector are operating properly.