Air/Fuel Ratio Control Caterpillar

The control is capable of self-diagnostics for the sensors, for the signals from the sensors, and for the motor for the fuel valve.

If an alarm condition is detected, the "ALARM" indicator on the control will illuminate. The output switch for the alarm will be activated.

"!" will follow the "MAN" mode or the "Auto" mode if the home status screen is active on the display screen. An "ALARM" message with a brief description of the condition will flash on the lower line of the display. The display screen will continue to display the active "ALARM" message when a diagnostic fault is present. The active "ALARM" messages are rotated to the bottom line of the home screen.

If all the diagnostic condition becomes inactive, the "ALARM" indicator and the "WARNING" screen will be deactivated.

"ALARM ACK" key - Press this key in order to acknowledge an alarm. This will deactivate the output switch for the alarm. The "ALARM" indicator will flash and full access to the functions of the keypad will be re-enabled.

There are 12 different specific diagnostic conditions which may be reported.

"ALARM LEAN LIMIT" (Maximum)

Illustration 1	g01389913

The "ALARM LEAN LIMIT" message indicates that the position of the fuel valve has reached the maximum limit of 1700 steps. The control has determined that the air/fuel mixture is too rich but the control cannot lean the mixture because the fuel valve is at the leanest limit.

Possible Causes

• The NO_X sensor is not operating or calibrated.

• The fuel pressure to the engine is too high.

• The load control valve is allowing too much fuel to enter the inlet manifold.

• The setpoint for the NO_X target is beyond the capability of the engine's operation.

• The harness for the fuel valve's motor is disconnected.

• The fuel valve's motor is damaged.

• The circuit driver for the fuel valve's motor is damaged.

• There is some other problem with the fuel system.

"ALARM RICH LIMIT" (Minimum)

Illustration 2	g01410681

The "ALARM RICH LIMIT" message indicates that the position of the fuel valve has reached the minimum limit of 0 steps. The control has determined that the air/fuel mixture is too lean but the control cannot richen the mixture because the fuel valve is at the richest limit.

Possible Causes

• The NO_X sensor is not operating or calibrated.

• The fuel pressure to the engine is too low.

• The load control valve is not allowing enough fuel to enter the inlet manifold.

• The setpoint for the NO_X target is beyond the capability of the engine's operation.

• The harness for the fuel valve's motor is disconnected.

• The fuel valve's motor is damaged.

• The circuit driver for the fuel valve's motor is damaged.

• There is some other problem with the fuel system.

"ALARM IMAP PWMhi"

Illustration 3	g01389930

The "ALARM IMAP PWMhi" message indicates that the duty cycle of the manifold air pressure sensor is greater than 95 percent.

Possible Causes

• The sensor's return wire has an open circuit.

• The signal wire has a short circuit to positive voltage.

• There is a problem with the sensor.

"ALARM IMAP PWMlo"

Illustration 4	g01389934

The "ALARM IMAP PWMlo" message indicates that the duty cycle of the manifold air pressure sensor is less than five percent.

Possible Causes

• The sensor is not connected.

• The supply wire has an open circuit or the wire is shorted to ground. Check for 24 volts at the connector for the sensor.

• The signal wire has an open circuit or the signal wire has a short to the common circuit.

• There is a problem with the sensor.

"ALARM NOx DRIVER"

Illustration 5	g01389944

The "ALARM NOx Driver" message indicates that the sensor is not working properly and that there may be a problem with the power to the sensor.

Possible Causes

• The power input for the NO_X sensor has failed due to a short to ground. Disconnect the sensor.

• The power to the sensor is shorted to ground.

• The control may have an internal fault of the logic board that relates to the hardware or the software.

"ALARM IntF"

Illustration 6	g01390058

The "ALARM IntF" message indicates that there is a problem within the air/fuel ratio control that relates to the signals that read data from the NO_X sensor.

Possible Causes

• The control may have an internal fault of the logic board that relates to the hardware or the software.

"ALARM CAN BUS"

Illustration 7	g01390110

The "ALARM CAN BUS" message indicates that there is a problem that relates to the communication between the control and the NO_X sensor over the bus for the CAN data link.

Possible Causes

• The termination resistor may not be present on the wiring harness near the NO_X sensor.

• An issue with the hardware that relates to the CAN bus port for the NO_X sensor may be causing errors on the bus.

• An issue with the hardware that relates to the air/fuel ratio control for the CAN bus port may be causing errors on the bus.

"ALARM NOx NoPGN"

Illustration 8	g01390068

The "ALARM NOx NoPGN" message indicates that there is no data being received from the NO_X sensor on the CAN bus.

Possible Causes

• The NO_X sensor may not be present. The NO_X sensor is unplugged from the harness.

• The power connection for the NO_X sensor may have an open circuit. Verify that 24 volts are present at the sensor connection.

• An open circuit or a short circuit to the CAN bus may be disrupting communication.

• The NO_X sensor may not be operating properly.

• The air/fuel ratio control may not be operating properly.

• The surge suppressor that is located by the NO_X sensor may not be operating properly.

"ALARM NOxErratic"

Illustration 9	g01390072

The "ALARM NOxErratic" message indicates that the NO_X sensor is reporting a condition that is not valid for the NO_X data.

Possible Causes

• Engine operation is very lean or very rich. The exhaust NO_X is outside the limits of measurement.

• Engine operation is very lean or very rich. The NO_X sensor is recovering from being outside of limits of measurement.

• The dynamics of engine operation has caused NO_X measurements that are erratic or out of limits.

• The NO_X sensor is loose in the mounting hole. An exhaust leak or a malfunction may be present.

• The NO_X sensor is damaged. The NO_X sensor may have matured beyond the sensor's useful operation.

"ALARM NOx Fault"

Illustration 10	g01390081

The "ALARM NOx Fault" message indicates that the NO_X sensor is reporting an operational internal fault condition.

Possible Causes

• A sensor wire between the sensing element and the sensor module may be broken or shorted.

• Operating conditions of the engine may be unacceptable for proper operation of the sensor.

• The NO_X sensor is damaged. The NO_X sensor may have matured beyond the sensor's useful operation.

"ALARM NOx Vspply"

Illustration 11	g01390088

The "ALARM NOx Vspply" message indicates that the supply voltage for the NO_X sensor is out of the sensor's value range. The sensor reading is not valid.

Possible Causes

• The supply voltage to the system is below 15 volts or above 35 volts.

• There is a poor connection between the power input for the NO_X sensor and the power output for the control.

• The power switch for the control is limiting the current by reducing the voltage.

"ALARM NOx TimOut"

Illustration 12	g01390099

The "ALARM NOx TimOut" message indicates that the NO_X sensor has not reached operating temperature within a reasonable time. The default setting is 1200 seconds.

Possible Causes

• The ambient condition of the engine application is too cold and/or the engine exhaust is very cool.

• The supply voltage to the system may be low resulting in insufficient heater performance for the conditions.

• The NO_X heater may be damaged. The NO_X heater has matured beyond the heater's useful service life.