Gauge Pack - Operation

OPERATION

GAUGES

All gauges receive battery current through the Instrument panel Cluster (IPC) 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 IPC 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.

Only the Tachometer and the Speedometer of the IPC 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 IPC 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. Unlike the tachometer and the speedometer, the fuel level gauge and the engine temperature gauges are electronic bar graph gauges located within the Electronic Vehicle Information Center (EVIC).

ENGINE TEMPERATURE

The engine temperature gauge gives an indication to the vehicle operator of the level of vehicle engine coolant temperature. This gauge is controlled by the IPC circuit board based upon programming and electronic messages received from the Powertrain Control Module (PCM) over the CAN data bus via the Body Control Module (BCM). The BCM acts as a central gateway between the CAN-B and CAN-C data buses.

The engine coolant temperature gauge is an electronic bar graph gauge within the EVIC that receives battery current on the IPC electronic circuit board through the fused ignition switch output (run-start) circuit whenever the ignition switch is in the ON or START positions. The IPC is programmed to move the bar graph back to the low end of the scale after the ignition switch is turned to the Off position. The IPC circuitry controls the gauge bar graph position, and provides the following features:

- Engine Temperature Message - Each time the IPC receives an electronic engine temperature message from the BCM indicating the temperature is between the low end of normal [about 104 °F (40 °C)], and the high end of normal [about 248° F (120 °C)], the gauge is moved to the actual relative temperature position on the gauge scale.
- Engine Temperature Low Message - Each time the IPC receives an electronic engine temperature message from the PCM via the BCM over the CAN data bus, indicating the temperature is low [at or below about 104 °F (40 °C), the gauge is held at the lower end of the gauge scale. The gauge remains below the low end of the gauge scale until the IPC receives a message indicating that the temperature is above the low end of normal, or until the ignition switch is turned to the OFF position, whichever occurs first.
- Engine Temperature High or Critical Message - Each time the IPC receives an electronic engine temperature message from the PCM via the BCM over the CAN data bus, indicating the temperature is high [at or above about 248° F (120° C)], the gauge is moved to the high end of the gauge scale, the engine temperature indicator is illuminated and a single chime tone is sounded. The gauge needle remains at the high end of the scale, and the engine temperature indicator remains illuminated until the IPC receives a message indicating that the temperature is below about 248° F (120° C), 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 messages from the PCM.
- Communication Error - If the IPC fails to receive an engine temperature message, it will hold the gauge 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 IPC will move the gauge 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 IPC. If the IPC 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 IPC circuit board based upon programming and electronic messages received from the BCM over the CAN data bus. The BCM receives a hard-wired input from the fuel level sending unit the fuel tank, and then transmits the fuel level information to the IPC over the CAN data bus.

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

- Fuel Level Message - The BCM 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 rises and decreases as the fuel level falls causing changes in the fuel level sense input voltage. The BCM then sends the appropriate electronic fuel level messages to the IPC. The IPC programming applies an algorithm to calculate the proper fuel gauge position based upon the fuel level message 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 BCM.
- Less Than 11 Percent Tank Full Message - Each time the fuel level message to the IPC indicates the fuel tank is about 11 percent full or less for 10 consecutive seconds and the vehicle speed is zero, or for 60 consecutive seconds and the vehicle speed is greater than zero, the gauge needle is moved to about the one-sixteenth 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 message indicates that the fuel tank is greater than about 14 percent full for 10 consecutive seconds and the vehicle speed is zero, or for 60 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 messages from the BCM.
- Less Than Empty Stop Message - Each time the IPC receives a fuel level message indicating the fuel level in the fuel tank is less than the E (or Empty) for five consecutive seconds, the gauge 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 BCM is a short circuit.
- More Than Full Stop Message - Each time the IPC receives a fuel level message indicating the fuel level in the fuel tank is more than the F (or Full) for five consecutive seconds, the gauge 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 BCM is an open circuit.

The BCM continually monitors the fuel tank sending unit to determine the level of fuel in the fuel tank. The BCM then sends the proper fuel level messages to other electronic modules in the vehicle over the CAN data bus. The fuel gauge is only 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 IPC circuit board based upon programming and electronic messages received from the BCM. The BCM provides the vehicle speed information across the CAN-B, and CAN-C data buses for use other modules within the vehicle.

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

- Vehicle Speed Message - Each time the IPC receives an electronic 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 IPC will receive a new message and reposition the gauge pointer accordingly. 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 IPC fails to receive a 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 vehicle speed sensor to determine the vehicle road speed. The PCM then sends the proper vehicle speed messages to the BCM over the CAN data bus. The speedometer can only be 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 IPC circuit board based upon programming and electronic messages received from the BCM over the CAN data bus. The BCM provides the vehicle speed information across the CAN-B, and CAN-C data buses for use other modules within the vehicle.

The tachometer is a stepper motor design gauge that receives battery current on the IPC electronic circuit board through the fused ignition switch output (run-start) circuit whenever the ignition switch is in the ON or START positions. The IPC 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 IPC circuitry controls the gauge needle position and provides the following features:

- Engine Speed Message - Each time the IPC receives an electronic engine speed message from the BCM it will calculate the correct engine speed reading and position the gauge needle at that relative speed position on the gauge scale. The IPC will receive a new message and reposition the gauge pointer accordingly. 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 IPC fails to receive a 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 IPC via BCM over the CAN-B and CAN-C data buses. The tachometer can only be serviced as a unit with the instrument cluster.