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. A functioning oxygen sensor heater will allow the sensor to produce voltage in a short amount of time. A sensor at operating temperature will cause the HO2S signal voltage to go above or below (depending upon exhaust oxygen content) the bias voltage.

This DTC is used to indicate an HO2S signal voltage that did not leave the cold sensor bias voltage range in an acceptable amount of time.

CONDITIONS FOR RUNNING THE DTC
^ The engine is operating on alternative fuel.
^ No Alternative Fuels ECM ECT DTCs are set.
^ The start-up engine coolant temperature is less than 33°C (91°F).
^ The engine has been operating for at least 5 seconds.
^ The average mass air flow is less than 35 grams per second.
^ The battery voltage is more than 8 volts.
^ All other Alternative Fuels ECM DTCs for this HO2S sensor have ran and passed.
^ This DTC has not tested this ignition cycle.
^ The Alternative Fuels ECM determines the HO2S was cold at ignition key ON. A cold HO2S is indicated when the average HO2S signal voltage is within the bias voltage range of 0.30 volts (300 mV) to 0.60 volts (600 mV) when the ignition is turned ON.

CONDITIONS FOR SETTING THE DTC
The Alternative Fuels ECM monitors an HO2S signal voltage that did not leave the cold sensor bias voltage range 0.30 volts (300 mV) to 0.60 volts (600 mV) in an acceptable amount of time. The time varies from 50 seconds to 110 seconds based upon mass airflow.

ACTION TAKEN WHEN THE DTC SETS
^ 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 7-15:

Steps 16-18:

The numbers below refer to the step numbers on the diagnostic table.
2. As the heater warms the oxygen sensor to operating temperature, the HO2S will output a voltage in relation to the amount of oxygen in the exhaust. With the ignition ON and the engine OFF, the exhaust usually contains a high oxygen content. With the engine OFF, the HO2S voltage will usually decrease from the initial (bias) voltage due to the high oxygen content.
6. This step tests for a proper HO2S heater ignition feed and ground supply.
7. This step tests for proper Control Module and signal circuit operation.