AFO Signal: Display shows PCM or AF ECM. This display monitors the vehicles GASOLINE Control Module (VCM/PCM or ECM) AFO Enable Input circuit. Alternative fuel operation is requested when the AF ECM grounds the Enable circuit to the gasoline control module. This display is received through serial data from the gasoline control module and NOT the AF ECM.

AFO Signal Command: Display shows PCM or AF ECM. This display monitors the AF ECM AFO Enable circuit output driver. Alternative fuel operation is requested when the AF ECM grounds the AFO Enable circuit to the gasoline control module.

AFO Enable Circuit Status: Display shows OK, Short to Ground, Short to Voltage. This display indicates the monitored status of the output driver circuit for this output. OK should always be indicated unless a circuit fault is monitored. This display is only active when the engine is operating on CNG.

Alternative Fuel Level: Display shows fuel level from 0-100%. This display indicates the fuel level signal being sent to the vehicles fuel level gage. The AF ECM monitors the fuel pressure sensor and the fuel temperature sensor values in order to determine the usable CNG fuel level.

Alternative Fuel Mileage Log: Display shows miles the vehicle has operated using alternative fuel.

Alternative Fuel Run Time Log: Display shows Hours: minutes: seconds. This display shows the amount of time the engine has operated using alternative fuel.

Battery Voltage: Display shows voltage from 0-25.5 volts. This display indicates the system voltage measured by the AF ECM at the battery feed terminal.

ECT Sensor: Display shows the temperature of the engine coolant from -40 to +155°C (-40 to +304°F) and the sensor voltage from 0.0-5.00.

Engine Load: Display shows engine load in percentage from 0-100%. Engine load is calculated by the AF ECM by engine speed and manifold absolute pressure. Reading should increase with an increase in RPM and MAP.

Engine Run Time: Display shows Hours: minutes: seconds. Engine run time measures how long the engine has been running during this ignition cycle. When the engine is turned OFF, the timer is reset to zero.

Engine Speed: Display shows crankshaft rotation speed in revolutions per minute (RPM) from 0-16384. The maximum engine speed is limited to 5500 RPM by the AF ECM during alternative fuel operation.

EVAP Purge Solenoid Command: Display shows percent. This display indicates the amount of gasoline EVAP purge that the gasoline control module (PCM, VCM or ECM) is commanding. The AF ECM uses this information for fuel trim adjustments while the engine is operating on CNG.

EVAP Purge Solenoid Reduce Request Command: Display shows NORMAL or REDUCE. This display indicates that the AF ECM is commanding the gasoline control module (VCM, PCM or ECM) to allow normal EVAP purge operation or to reduce the amount of EVAP purge duty cycle. The AF ECM will request a reduction in EVAP purge whenever the engine is operating in CNG Open Loop fuel control.

EVAP Reduce Request Circuit Status: Display shows OK, Short to Ground, Short to Voltage. This display indicates the monitored status of the output driver circuit for this output. OK should always be indicated unless a circuit fault is monitored. This display is only active when the engine is operating on CNG.

Fuel Control PWM Signal Command: Display shows percent from 0-100. This display indicates the duty cycle ON time in percent for the Fuel Control Solenoid (FCS). A high percentage indicates the AF ECM is leaning out the fuel mixture. A low percentage indicates the AF ECM is richening the fuel mixture.

Fuel Control Circuit Status: Display shows OK, Short to Ground, Short to Voltage. This display indicates the monitored status of the output driver circuit for the fuel control solenoid. OK should always be indicated unless a circuit fault is monitored. This display is only active when the engine is operating on CNG.

Fuel Gage Relay Command: Display shows GASOLINE or ALT. FUEL. This display indicates the commanded state of the fuel gage relay. The commanded state indicates which fuel system fuel level will be displayed by the instrument panel fuel gage. The AF ECM will change the commanded state of the fuel gage relay for about 10 seconds whenever the fuel gage select switch is depressed.

Fuel Gage Select Switch: Display shows DEPRESSED or RELEASED. This display indicates the state of the fuel gage select switch button. Depressing the button causes the DORMANT fuel system fuel level to be displayed on the instrument panel fuel gage for about 10 seconds. The AF ECM operates the fuel gage relay in order to change the fuel level signal input to the instrument panel fuel gage.

Fuel Gage Circuit Status: Display shows OK, Short to Ground, Short to Voltage. This display indicates the monitored status of the output driver circuit for this output. OK should always be indicated unless a circuit fault is monitored. This display is only active when the engine is operating on CNG.

Fuel Indicator Lamp Command: Display shows ON or OFF. This display indicates the commanded state of the fuel indicator lamp (FIL) located within the fuel gage select switch button. The lamp is illuminated for a 2 second bulb check at ignition ON and also when the engine is operating on gasoline.

(Alt. Fuel) Fuel Pump Relay Command: Display shows ON or OFF. The display indicates the commanded state of the AF Fuel Pump relay. The gasoline fuel pump power circuit is routed through the AF Fuel Pump relay. Whenever the engine is operating on alternative fuel the AF ECM commands the AF Fuel pump relay ON, opening the gasoline fuel pump power circuit. The AF ECM opens the gasoline fuel pump power circuit in order to prevent unnecessary gasoline fuel pump operation.

Fuel Pressure Sensor: Display shows voltage from 0.0-5.0 and pressure from 0-4064 psi. This display indicates the CNG fuel tank pressure. The AF ECM monitors the fuel tank pressure sensor and the fuel tank temperature sensor in order to calculate the correct CNG fuel level remaining in the tank.

Fuel Temperature Sensor: Display shows voltage from 0.0 to 5.0 and temperature from -40 to +150°C (-40 to +302°F). This display indicates the temperature of the CNG fuel within the fuel tank. The AF ECM monitors the fuel tank pressure sensor and the fuel tank temperature sensor in order to calculate the correct CNG fuel level remaining in the tank. The fuel tank temperature sensor is an integral part of the high pressure lock-off assembly.

Gasoline Fuel Mileage Log: Display shows miles the vehicle has operated using gasoline fuel.

Gasoline Fuel Run Time Log: Display shows Hours: minutes: seconds. This display shows the amount of time the engine has operated using gasoline fuel.

High Pressure Lockoff Relay Command: Display shows OPEN or CLOSED. This display indicates the commanded state of the high pressure lock-off relay. The AF ECM opens the HPL's for 1 second at EVERY ignition ON in order to supply a prime pulse to the CNG fuel system.

HPL Solenoid Output Circuit Status: Display shows OK, Short to Ground, Short to Voltage. This display indicates the monitored status of the output driver circuit for the HPL Lock-off relay. OK should always be indicated unless a circuit fault is monitored. This display is only active when the engine is operating on CNG.

HO2S Bank 1 Sensor 1: Display shows voltage from 0.0-1.1 volts. This display indicates the voltage of the O2 sensor High signal circuit. With a COLD O2 sensor the signal circuit BIAS voltage of about 451 mV should be displayed. The oxygen sensor will produce voltage in relation to exhaust oxygen content once the oxygen sensor reaches operating temperature. High exhaust oxygen content, or LEAN conditions, will produce low voltage (100 mV). Low exhaust oxygen content, or RICH conditions, will produce high voltage (900 mV). With the oxygen sensor at operating temperature and the engine in Closed Loop operation the oxygen sensor voltage should rapidly fluctuate between low and high voltage.

HO2S Bank 2 Sensor 1: Display shows voltage from 0.0-1.1 volts. This display indicates the voltage of the O2 sensor High signal circuit. With a COLD O2 sensor the signal circuit BIAS voltage of about 451 mV should be displayed. The oxygen sensor will produce voltage in relation to exhaust oxygen content once the oxygen sensor reaches operating temperature. High exhaust oxygen content, or LEAN conditions, will produce low voltage (100 mV). Low exhaust oxygen content, or RICH conditions, will produce high voltage (900 mV). With the oxygen sensor at operating temperature and the engine in Closed Loop operation the oxygen sensor voltage should rapidly fluctuate between low and high voltage.

IAT Sensor: Display shows the temperature of the intake manifold air from -40 to +155°C (-40 to +304°F) and the sensor voltage from 0.0 to 5.00.

Idle Fuel Control PWM Signal Command: Display shows percent from 0-100. This display indicates the duty cycle ON time in percent for the idle control solenoid (ICS). A high percentage indicates the AF ECM is adding fuel for idle conditions.

Idle Control Circuit Status: Display shows OK, Short to Ground, Short to Voltage. This display indicates the monitored status of the output driver circuit for this output. OK should always be indicated unless a circuit fault is monitored. This display is only active when the engine is operating on CNG.

Ignition 0: Display shows voltage from 0-25.5 volts. This display indicates the system voltage measured by the AF ECM at the ignition feed terminal.

Long Term FT Avg.: Display shows percentage from -100 to +100%. The center position for the long term fuel trim is 0%. The long term fuel trim is based on short term fuel trim learned values. It is stored in memory blocks of the long term memory according to MAP and RPM values. A percentage greater than 0% indicates that time is being added to the Fuel Control solenoid pulse width, increasing the amount of fuel to the engine. A percentage less than 0% indicates time is being subtracted from the pulse width, reducing the amount fuel to the engine. A value of 0% indicates no compensation is required to operate the engine at the desired 16.8 to 1 air/fuel ratio.

Loop Status: Display shows OPEN LOOP or CLOSED LOOP. Closed Loop displayed indicates that the AF ECM is controlling fuel delivery according to oxygen sensor voltage. In Open Loop, the AF ECM ignores the oxygen sensor voltage and bases the amount of fuel to be delivered on other input sensors. At extremely high ambient temperatures or when towing a trailer, it is possible for the system to remain in Open Loop operation in order to control catalytic converter temperatures.

Low Pressure Lockoff Solenoid Command: Display shows OPEN or CLOSED. This display indicates the commanded state of the low pressure lock-off solenoid. During alternative fuel operation conditions the LPL remains closed until at least 25 RPM is monitored by the AF ECM.

LPL Solenoid Output Circuit Status: Display shows OK, Short to Ground, Short to Voltage. This display indicates the monitored status of the output driver circuit for this output. OK should always be indicated unless a circuit fault is monitored. This display is only active when the engine is operating on CNG.

MAF Sensor: Display shows the amount of airflow entering the engine in grams per second (g/s) from 0-512 and in frequency from 0-31,999 Hz. The MAF sensor produces a frequency signal equal to 2.4 g/s whenever the ignition is ON and the engine is OFF. The 2.4 g/s signal is necessary in order to detect circuit faults. A loss of the MAF sensor signal to the AF ECM would result in 0.0 g/s airflow being displayed.

MAP Sensor: Display shows manifold pressure in Kilo Pascals (Kpa) from 10-104 and voltage from 0-5.0. At key ON , engine not running, the MAP value will reflect barometric pressure. To check for an accurate MAP reading multiply your local barometric pressure by 3.386 to obtain a map value that should be within 2 Kpa of displayed value at key ON , engine not running.

(Gasoline) MIL Command: Display shows ON or OFF. The MIL is controlled by both the AF ECM and the gasoline control module (VCM / PCM or ECM). This display indicates ON whenever the GASOLINE control module commands the MIL ON. The internal circuitry of the AF ECM monitors, but does not affect, the gasoline control modules operation of the MIL. The MIL is illuminated if either module has detected a problem that affects vehicle emissions, driveabillity or could cause powertrain damage. The gasoline control module illuminates the MIL when the ignition is ON and the engine OFF in order to perform a bulb test.

(Alt. Fuel) MIL Command: Display shows ON or OFF. The MIL is controlled by both the AF ECM and the gasoline control module (VCM / PCM or ECM). The (AF ECM) MIL COMMAND indicates ON whenever the MIL Control (AF ECM) output circuit is commanding the MIL ON. The MIL is illuminated if either module has detected a problem that affects vehicle emissions, driveability or could cause powertrain damage.

MIL Output CKT Status: Display shows OK, OPEN, SHORT or OVERTEMPERATURE. This display indicates the monitored status of the output driver circuit for this output. OK should always be indicated unless a circuit fault is monitored.

Reference Voltage High: Display shows voltage from 0.0 to 5.2 volts. This display indicates the voltage monitored by the AF ECM from the gasoline control module 5 volt sensor supply circuit.

Reference Voltage Low: Display shows voltage from 0.0 to 5.2 volts. This display indicates the voltage monitored by the AF ECM from the gasoline control module 5 volt sensor return circuit.

Short Term FT Avg.:  Display shows percentage from -100 to +99%. The center position for the short term fuel trim is 0%. A percentage greater than 0% indicates that time is being added to the Fuel Control solenoid pulse width, increasing the amount of fuel to the engine to compensate for a lean condition sensed by the average of both the oxygen sensors. A percentage less than 0% indicates time is being subtracted from the pulse width reducing the amount of fuel to the engine to compensate for a rich condition sensed by the oxygen sensor. A value of 0% indicates no compensation is required to operate the engine at the desired 16.8 to 1 air/fuel ratio.

TP Sensor: Display shows throttle angle from 0-100% and sensor voltage from 0.0-5.0 volts. The % display indicates the throttle angle opening from closed (0%) to fully open (100%). The AF ECM learns the closed throttle position whenever the TP sensor voltage is below about 0.9 volts. Learning the closed throttle position is necessary in order to adjust for production tolerances. The voltage display indicates the throttle angle opening from closed (about 0.5 volts) to fully open (about 4.0 volts).

Vehicle Speed Sensor: Display shows vehicle speed from 0-255 km/h (0-155 mph). The maximum vehicle speed is limited to 169 km/h (107 mph) by the AF ECM during alternative fuel operation.