For 1990-2009 cars only
5 Volt Ref. High: Display shows voltage from 0.0 to 5.2 volts. This display
indicates the voltage monitored by the AF ECU from the gasoline control module
5 volt sensor supply circuit.
5 Volt Ref. Low: Display shows voltage from 0.0 to 5.2 volts. This display indicates the voltage monitored by the AF ECU from the gasoline control module 5 volt sensor return (ground) circuit.
Actual Gas Flow: Display shows the amount of alternative gas entering the engine in grams per second (g/s) from 0 to 20. This display indicates the amount of CNG entering the engine as measured by the gas mass sensor.
Alternative Fuel Level: Display shows fuel level from 0% to 100%. This display indicates the fuel level signal being sent to the vehicles fuel level gauge. The AF ECU monitors the fuel pressure sensor and the fuel temperature sensor values in order to determine the useable 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.
BARO: Display shows the BARO in Kpa from 11 to 105 and voltage from 0 to 5. The BARO reading is taken at key ON using the MAP sensor and is also corrected at wide open throttle (WOT). Multiply your current, local, barometric pressure by 3.386 to obtain a BARO value that should be within 2 Kpa of the displayed value.
Battery Voltage: Display shows voltage from 0 to 25.5. This display indicates the system voltage measured by the AF ECU at the battery feed terminal.
Calc. Air Flow: Display shows the amount of air flow in grams per second (g/s) from 0 to 512. This display indicates the amount of calculated airflow entering the engine. The AF ECU calculates this airflow based upon MAP sensor and IAT values.
Desired Gas Flow: Display shows the amount of desired alternative gas in grams per second (g/s) from 0 to 512. This display indicates the amount of CNG flow desired by the AF ECU.
ECT: Display shows the temperature of the engine coolant from -40° to 155°C ( -40° to 304°F).
ECT Sensor: Display shows voltage from 0.0 to 5.00
Engine Load: Display shows engine load in percent from 0 to 100. Engine load is calculated by the AF ECU 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 to 16384. The maximum engine speed is limited to 5500 RPM by the AF ECU during alternative fuel operation.
Fuel Gauge Relay: Display shows GASOLINE or ALT. FUEL. This display indicates the commanded state of the fuel gauge relay. The commanded state indicates which fuel system fuel level will be displayed by the instrument panel fuel gauge. The AF ECU will change the commanded state of the fuel gauge relay for about 10 seconds whenever the fuel gauge select switch is depressed.
Fuel Gauge Select Sw.: Display shows DEPRESSED or RELEASED. This display indicates the state of the fuel gauge select switch button. Depressing the button causes the DORMANT fuel system fuel level to be displayed on the instrument panel fuel gauge for about 10 seconds. The AF ECU operates the fuel gauge relay in order to change the fuel level signal input to the instrument panel fuel gauge.
Fuel Indicator Lamp: Display shows ON or OFF. This display indicates the commanded state of the fuel indicator lamp (FIL) located within the fuel gauge select switch button. The lamp is illuminated for a two second bulb check at ignition ON and also when the engine is operating on gasoline.
Fuel Pressure Sensor: Display shows voltage from 0.0 to 5.0 and pressure from 0 to 4064 psi. This display indicates the CNG fuel tank pressure. The AF ECU monitors the fuel pressure sensor and the fuel temperature sensor in order to calculate the correct CNG fuel level remaining in the tank.
Fuel Pump Relay (Alt. Fuel): 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 ECU commands the AF Fuel pump relay ON, opening the gasoline fuel pump power circuit. The AF ECU opens the gasoline fuel pump power circuit in order to prevent unecessary gasoline fuel pump operation.
Fuel Temperature Sensor: Display shows voltage from 0.0 to 5.0 and temperature from -40°C to 150°C (-40°F to 302°F). This display indicates the temperature of the CNG fuel within the fuel tank. The AF ECU monitors the fuel pressure sensor and the fuel temperature sensor in order to calculate the correct CNG fuel level remaining in the tank. The fuel temperature sensor is located within 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: Display shows OPEN or CLOSED. This display indicates the commanded state of the high pressure lock-off solenoid. The AF ECU opens the HPL for one second at EVERY ignition ON in order to supply a prime pulse to the CNG fuel system.
IAC Position: Display shows counts from 0 to 255. This display indicates the commanded position of the idle air control (IAC) valve pintle. When a higher idle engine speed is desired the control module will retract the IAC pintle, increasing airflow and increasing the count value. When a slower idle engine speed is desired the control module will extend the IAC pintle, decreasing airflow and decreasing the count value. 0 counts would indicate a fully closed IAC pintle
IAT: Display shows shows the temperature of the intake manifold air from -40° to 155°C (-40° to 304°F).
IAT Sensor: Display shows voltage from 0.0 to 5.00.
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 MCV pulse width, increasing the amount of fuel to the engine. A percentage less than 0% indicates time is being subtracted from the MCV 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 ECU is controlling fuel delivery according to oxygen sensor voltage. In Open Loop, the AF ECU 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: 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 (engine is cranking) is monitored by the AF ECU.
MAP: Display shows manifold pressure in Kilo Pascals (Kpa) from 10 to 104 and voltage from 0 to 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.
MIL Input (Gasoline): Display shows ON or OFF. The MIL (Service Engine Soon or Check Engine) is controlled by both the AF ECU and the gasoline control module (VCM / PCM or ECM). The MIL INPUT indicates ON whenever the GASOLINE control module commands the MIL ON. The internal circuitry of the AF ECU 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.
MIL Output (AF ECU): Display shows ON or OFF. The MIL (Service Engine Soon or Check Engine) is controlled by both the AF ECU and the gasoline control module (VCM / PCM or ECM). The MIL OUTPUT indicates ON whenever the MIL Control (AF ECU) 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.
Mixture Control Valve: Display shows frequency from 0 to 2000 Hz. This display indicates the frequency or PWM signal the AF ECU is commanding the Mixture Control Valve. A higher frequency indicates the AF ECU is commanding more gas (rich).
NGO Enable Input: Display shows GASOLINE or ALT. FUEL. This display monitors the vehicles GASOLINE Control Module (VCM/PCM or ECM) NGO Enable Input circuit. Alternative fuel operation is requested when the AF ECU grounds the NGO Enable circuit to the gasoline control module. This display is received from the gasoline control module and NOT the AF ECU.
NGO Enable Output: Display shows GASOLINE or ALT. FUEL. This display monitors the AF ECU NGO Enable circuit output driver. Alternative fuel operation is requested when the AF ECU grounds the NGO Enable circuit to the gasoline control module.
O2S 1: Display shows voltage from 0.0 to 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.
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 MCV 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 MCV 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 Angle: Display shows throttle angle from 0 to 100%. This display indicates the throttle angle opening from closed (0%) to fully open (100%). The AF ECU 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 tolerences.
TP Sensor: Display shows voltage from 0.0 to 5.0 volts. The TP sensor contains a potentiometer that provides a voltage proportional to the throttle angle. This display indicates the throttle angle opening from closed (about 0.5 volts) to fully open (about 4.0 volts).
Vehicle Speed: Display shows vehicle speed from 0 km/h (0 MPH) to 255 km/h (155 MPH). The maximum vehicle speed is limited to 107 MPH by the AF ECU during alternative fuel operation.
5 Volt Ref. Low: Display shows voltage from 0.0 to 5.2 volts. This display indicates the voltage monitored by the AF ECU from the gasoline control module 5 volt sensor return (ground) circuit.
Actual Gas Flow: Display shows the amount of alternative gas entering the engine in grams per second (g/s) from 0 to 20. This display indicates the amount of CNG entering the engine as measured by the gas mass sensor.
Alternative Fuel Level: Display shows fuel level from 0% to 100%. This display indicates the fuel level signal being sent to the vehicles fuel level gauge. The AF ECU monitors the fuel pressure sensor and the fuel temperature sensor values in order to determine the useable 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.
BARO: Display shows the BARO in Kpa from 11 to 105 and voltage from 0 to 5. The BARO reading is taken at key ON using the MAP sensor and is also corrected at wide open throttle (WOT). Multiply your current, local, barometric pressure by 3.386 to obtain a BARO value that should be within 2 Kpa of the displayed value.
Battery Voltage: Display shows voltage from 0 to 25.5. This display indicates the system voltage measured by the AF ECU at the battery feed terminal.
Calc. Air Flow: Display shows the amount of air flow in grams per second (g/s) from 0 to 512. This display indicates the amount of calculated airflow entering the engine. The AF ECU calculates this airflow based upon MAP sensor and IAT values.
Desired Gas Flow: Display shows the amount of desired alternative gas in grams per second (g/s) from 0 to 512. This display indicates the amount of CNG flow desired by the AF ECU.
ECT: Display shows the temperature of the engine coolant from -40° to 155°C ( -40° to 304°F).
ECT Sensor: Display shows voltage from 0.0 to 5.00
Engine Load: Display shows engine load in percent from 0 to 100. Engine load is calculated by the AF ECU 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 to 16384. The maximum engine speed is limited to 5500 RPM by the AF ECU during alternative fuel operation.
Fuel Gauge Relay: Display shows GASOLINE or ALT. FUEL. This display indicates the commanded state of the fuel gauge relay. The commanded state indicates which fuel system fuel level will be displayed by the instrument panel fuel gauge. The AF ECU will change the commanded state of the fuel gauge relay for about 10 seconds whenever the fuel gauge select switch is depressed.
Fuel Gauge Select Sw.: Display shows DEPRESSED or RELEASED. This display indicates the state of the fuel gauge select switch button. Depressing the button causes the DORMANT fuel system fuel level to be displayed on the instrument panel fuel gauge for about 10 seconds. The AF ECU operates the fuel gauge relay in order to change the fuel level signal input to the instrument panel fuel gauge.
Fuel Indicator Lamp: Display shows ON or OFF. This display indicates the commanded state of the fuel indicator lamp (FIL) located within the fuel gauge select switch button. The lamp is illuminated for a two second bulb check at ignition ON and also when the engine is operating on gasoline.
Fuel Pressure Sensor: Display shows voltage from 0.0 to 5.0 and pressure from 0 to 4064 psi. This display indicates the CNG fuel tank pressure. The AF ECU monitors the fuel pressure sensor and the fuel temperature sensor in order to calculate the correct CNG fuel level remaining in the tank.
Fuel Pump Relay (Alt. Fuel): 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 ECU commands the AF Fuel pump relay ON, opening the gasoline fuel pump power circuit. The AF ECU opens the gasoline fuel pump power circuit in order to prevent unecessary gasoline fuel pump operation.
Fuel Temperature Sensor: Display shows voltage from 0.0 to 5.0 and temperature from -40°C to 150°C (-40°F to 302°F). This display indicates the temperature of the CNG fuel within the fuel tank. The AF ECU monitors the fuel pressure sensor and the fuel temperature sensor in order to calculate the correct CNG fuel level remaining in the tank. The fuel temperature sensor is located within 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: Display shows OPEN or CLOSED. This display indicates the commanded state of the high pressure lock-off solenoid. The AF ECU opens the HPL for one second at EVERY ignition ON in order to supply a prime pulse to the CNG fuel system.
IAC Position: Display shows counts from 0 to 255. This display indicates the commanded position of the idle air control (IAC) valve pintle. When a higher idle engine speed is desired the control module will retract the IAC pintle, increasing airflow and increasing the count value. When a slower idle engine speed is desired the control module will extend the IAC pintle, decreasing airflow and decreasing the count value. 0 counts would indicate a fully closed IAC pintle
IAT: Display shows shows the temperature of the intake manifold air from -40° to 155°C (-40° to 304°F).
IAT Sensor: Display shows voltage from 0.0 to 5.00.
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 MCV pulse width, increasing the amount of fuel to the engine. A percentage less than 0% indicates time is being subtracted from the MCV 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 ECU is controlling fuel delivery according to oxygen sensor voltage. In Open Loop, the AF ECU 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: 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 (engine is cranking) is monitored by the AF ECU.
MAP: Display shows manifold pressure in Kilo Pascals (Kpa) from 10 to 104 and voltage from 0 to 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.
MIL Input (Gasoline): Display shows ON or OFF. The MIL (Service Engine Soon or Check Engine) is controlled by both the AF ECU and the gasoline control module (VCM / PCM or ECM). The MIL INPUT indicates ON whenever the GASOLINE control module commands the MIL ON. The internal circuitry of the AF ECU 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.
MIL Output (AF ECU): Display shows ON or OFF. The MIL (Service Engine Soon or Check Engine) is controlled by both the AF ECU and the gasoline control module (VCM / PCM or ECM). The MIL OUTPUT indicates ON whenever the MIL Control (AF ECU) 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.
Mixture Control Valve: Display shows frequency from 0 to 2000 Hz. This display indicates the frequency or PWM signal the AF ECU is commanding the Mixture Control Valve. A higher frequency indicates the AF ECU is commanding more gas (rich).
NGO Enable Input: Display shows GASOLINE or ALT. FUEL. This display monitors the vehicles GASOLINE Control Module (VCM/PCM or ECM) NGO Enable Input circuit. Alternative fuel operation is requested when the AF ECU grounds the NGO Enable circuit to the gasoline control module. This display is received from the gasoline control module and NOT the AF ECU.
NGO Enable Output: Display shows GASOLINE or ALT. FUEL. This display monitors the AF ECU NGO Enable circuit output driver. Alternative fuel operation is requested when the AF ECU grounds the NGO Enable circuit to the gasoline control module.
O2S 1: Display shows voltage from 0.0 to 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.
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 MCV 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 MCV 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 Angle: Display shows throttle angle from 0 to 100%. This display indicates the throttle angle opening from closed (0%) to fully open (100%). The AF ECU 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 tolerences.
TP Sensor: Display shows voltage from 0.0 to 5.0 volts. The TP sensor contains a potentiometer that provides a voltage proportional to the throttle angle. This display indicates the throttle angle opening from closed (about 0.5 volts) to fully open (about 4.0 volts).
Vehicle Speed: Display shows vehicle speed from 0 km/h (0 MPH) to 255 km/h (155 MPH). The maximum vehicle speed is limited to 107 MPH by the AF ECU during alternative fuel operation.
