Gauge Pack - Operation

OPERATION

GAUGES

All gauges receive battery current through the Instrument Cluster (IC) circuitry only when the ignition switch is in the ON or START positions. With the ignition switch in the OFF position battery current is not supplied to any gauges, and the IC circuitry is programmed to move all of the gauge needles back to the low end of their respective scales. Therefore, the gauges do not accurately indicate any vehicle condition unless the ignition switch is in the ON or START positions.

All of the IC gauges are driven by stepper motors. Two fixed electromagnetic coils are located within each gauge. These coils are wrapped at right angles to each other around a movable permanent magnet. The movable magnet is suspended within the coils on one end of a pivot shaft, while the gauge needle is attached to the other end of the shaft. One of the coils has a fixed current flowing through it to maintain a constant magnetic field strength. Current flow through the second coil changes, which causes changes in its magnetic field strength. The current flowing through the second coil is changed by the IC circuitry in response to messages received over the CAN data bus. The gauge needle moves as the movable permanent magnet aligns itself to the changing magnetic fields created around it by the electromagnets.

ENGINE COOLANT TEMPERATURE GAUGE

This gauge is controlled by the IC circuit board based upon programming and electronic messages received from the Powertrain Control Module (PCM) over the CAN data bus.

The engine coolant temperature gauge is a stepper motor design gauge that receives battery current on the instrument IC electronic circuit board through the fused ignition switch output (run-start) circuit whenever the ignition switch is in the ON or START positions. The IC is programmed to move the gauge needle back to the low end of the scale after the ignition switch is turned to the Off position. The IC circuitry controls the gauge needle position and provides the following features:

- Engine Temperature Message - Each time the IC receives a message from the PCM indicating the engine coolant temperature is between the low end of normal [about 54° C (130° F)] and the high end of normal [about 127° C (260° F)], the gauge needle is moved to the actual relative temperature position on the gauge scale.
- Engine Temperature Low Message - Each time the IC receives a message from the PCM indicating the engine coolant temperature is below the low end of normal [about 54° C (130° F)], the gauge needle is held at the "C" increment at low end of the gauge scale. The gauge needle remains at the low end of the gauge scale until the IC receives a message from the PCM indicating that the engine temperature is above about 54° C (130° F), or until the ignition switch is turned to the Off position, whichever occurs first.
- Engine Temperature High Message - Each time the IC receives a message from the PCM indicating the engine coolant temperature is above about 127° C (260° F), the gauge needle is moved into the red zone on the gauge scale, the engine temperature indicator is illuminated, and a single chime tone is sounded. The gauge needle remains in the red zone and the engine temperature indicator remains illuminated until the IC receives a message from the PCM indicating that the engine temperature is below about 127° C (260° F), or until the ignition switch is turned to the Off position, whichever occurs first. The chime tone feature will only repeat during the same ignition cycle if the engine temperature indicator is cycled off and then on again by the appropriate engine temperature messages from the PCM.
- Communication Error - If the IC fails to receive an engine temperature message, it will hold the gauge needle at the last indication for about five seconds or until the ignition switch is turned to the Off position, whichever occurs first. After five seconds, the IC will move the gauge needle to the low end of the gauge scale.

The PCM continually monitors the engine coolant temperature sensor to determine the engine operating temperature. The PCM then sends the proper engine coolant temperature messages to the IC. For further diagnosis of the engine coolant temperature gauge or the IC circuitry that controls the gauge, Testing and Inspection. If the IC turns on the engine temperature indicator due to a high engine temperature gauge reading, it may indicate that the engine or the engine cooling system requires service. The engine coolant temperature gauge is serviced as a unit with the instrument cluster.

FUEL GAUGE

The fuel gauge gives an indication to the vehicle operator of the level of fuel in the fuel tank. This gauge is controlled by the IC circuit board based upon programming and a hard wired input received from the fuel level sending unit on the fuel pump module in the fuel tank.

The fuel gauge is a stepper motor design gauge that receives battery current on the IC electronic circuit board through the fused ignition switch output (run-start) circuit whenever the ignition switch is in the On or Start positions. The IC is programmed to move the gauge needle back to the low end of the scale after the ignition switch is turned to the Off position. The IC circuitry controls the gauge needle position and provides the following features:

- Fuel Level Sending Unit Input - The IC provides a constant current source to the fuel level sending unit and monitors a return input on a fuel level sense circuit. The resistance through the fuel level sending unit increases as the fuel level falls and decreases as the fuel level rises causing changes in the sense input voltage. The IC programming applies an algorithm to calculate the proper fuel gauge needle position based upon the fuel level sense input, then moves the gauge needle to the proper relative position on the gauge scale. This algorithm is used to dampen gauge needle movement against the negative effect that fuel sloshing within the fuel tank can have on accurate inputs from the fuel tank sending unit to the IC.
- Less Than Ten Percent Tank Full Input The LX is equipped with two tank sizes : an 18 gallon and a 19 gallon. This is a saddle type tank with a sending unit on each side. The sending units are hard-wired to the IC. The IC will average the sending unit voltages and provide the proper gauge positioning. Each time the fuel level sense input to the IC indicates the fuel tank is about ten percent full or less for ten consecutive seconds and the vehicle speed is zero, or for sixty consecutive seconds and the vehicle speed is greater than zero, the gauge needle is moved to about the one-eighth graduation on the gauge scale, the low fuel indicator is illuminated, and a single chime tone is sounded. The low fuel indicator remains illuminated until the fuel level sense input indicates that the fuel tank is greater than about thirteen percent full for ten consecutive seconds and the vehicle speed is zero, or for sixty consecutive seconds and the vehicle speed is greater than zero, or until the ignition switch is turned to the Off position, whichever occurs first. The chime tone feature will only repeat during the same ignition cycle if the low fuel indicator is cycled off and then on again by the appropriate inputs from the fuel level sending unit.
- Less Than Empty Stop Input - Each time the IC receives a fuel level sense input that indicates the fuel level in the fuel tank is less than the Empty gauge needle stop position, the gauge needle is moved to the low end of the gauge scale and the low fuel indicator is illuminated immediately. This input would indicate that the fuel level sense input to the IC is a short circuit.
- More Than Full Stop Input - Each time the IC receives a fuel level sense input that indicates the fuel level in the fuel tank is more than the Full gauge needle stop position, the gauge needle is moved to the low end of the gauge scale and the low fuel indicator is illuminated immediately. This input would indicate that the fuel level sense input to the IC is an open circuit.

The IC continually monitors the fuel tank sending unit to determine the level of fuel in the fuel tank. The IC then sends the proper fuel level messages to other electronic modules in the vehicle over the CAN data bus. For further diagnosis of the fuel gauge or the IC circuitry that controls the gauge, Testing and Inspection. The fuel gauge is serviced as a unit with the instrument cluster.

SPEEDOMETER

The speedometer gives an indication to the vehicle operator of the vehicle road speed. This gauge is controlled by the IC circuit board based upon programming and electronic messages received from the Body Control Module (BCM) (also known as the Common Body Controller/CBC). The BCM is provided the vehicle speed information across the CAN data bus by either the PCM, the ESP module or the ABS module.

The IC circuitry controls the gauge needle position and provides the following features:

- Vehicle Speed Message - Each time the IC receives a vehicle speed message from the BCM, it will calculate the correct vehicle speed reading and position the gauge needle at that relative speed position on the gauge scale. The IC will receive a new vehicle speed message and reposition the gauge pointer accordingly about every 50 milliseconds. The gauge needle will continually be positioned at the relative vehicle speed position on the gauge scale until the vehicle stops moving, or until the ignition switch is turned to the OFF position, whichever occurs first.
- Communication Error - If the IC fails to receive a speedometer message, it will hold the gauge needle at the last indication for about three seconds, or until the ignition switch is turned to the Off position, whichever occurs first. After three seconds, the gauge needle will return to the left end of the gauge scale.

The PCM continually monitors the vehicle speed sensor to determine the vehicle road speed. The PCM then sends the proper vehicle speed messages to the IC. For further diagnosis of the speedometer or the IC circuitry that controls the gauge, Testing and Inspection. The speedometer is serviced as a unit with the instrument cluster.

TACHOMETER

The tachometer gives an indication to the vehicle operator of the engine speed. This gauge is controlled by the IC circuit board based upon programming and electronic messages received from the PCM over the CAN data bus.

The tachometer is a stepper motor design gauge that receives battery current on the IC electronic circuit board through the fused ignition switch output (run-start) circuit whenever the ignition switch is in the ON or START positions. The IC is programmed to move the gauge needle back to the low end of the scale after the ignition switch is turned to the OFF position. The IC circuitry controls the gauge needle position and provides the following features:

- Engine Speed Message - Each time the IC receives an engine speed message from the PCM it will calculate the correct engine speed reading and position the gauge needle at that relative speed position on the gauge scale. The IC will receive a new engine speed message and reposition the gauge pointer accordingly about every 88 milliseconds. The gauge needle will continually be repositioned at the relative engine speed position on the gauge scale until the engine stops running, or until the ignition switch is turned to the OFF position, whichever occurs first.
- Communication Error - If the IC fails to receive an engine speed message, it will hold the gauge needle at the last indication for about three seconds, or until the ignition switch is turned to the Off position, whichever occurs first. After three seconds, the gauge needle will return to the left end of the gauge scale.

The PCM continually monitors the crankshaft position sensor to determine the engine speed. The PCM then sends the proper engine speed messages to the IC. For further diagnosis of the tachometer or the IC circuitry that controls the gauge, Testing and Inspection. The tachometer is serviced as a unit with the instrument cluster.

The gauges are diagnosed using the IC self-diagnostic test Testing and Inspection. Proper testing of the CAN data bus and the electronic data bus message inputs to the IC that control each gauge require the use of a diagnostic scan tool. Refer to the appropriate diagnostic information.