Principles of Operation

PRINCIPLES OF OPERATION

The instrument cluster gauges are not installed separately. The instrument cluster illumination lamps, warning indicator lamps, transmission range selector, and the instrument cluster lens and mask are the only parts that may be installed separately.

Speedometer/Odometer
The instrument cluster receives vehicle speed information from the powertrain control module (PCM) over the communication network. On vehicles equipped with gasoline engines, the PCM receives its signal from the output shaft speed sensor (OSS). On vehicles equipped with diesel engines, the PCM receives its signal from the vehicle speed sensor (VSS).

The SELECT/RESET button has 3 functions. First, pressing the SELECT/RESET button toggles between the odometer and trip odometer settings. When the trip odometer is displayed, pressing and holding the SELECT/RESET button resets the trip odometer. There are 2 trip odometers available. Pressing the SELECT/RESET button while in trip odometer toggles between trip odometer A and trip odometer B. Lastly, the instrument cluster self-test is entered by pressing and holding the SELECT/RESET button down with the ignition switch in the OFF position, then turning the ignition switch to RUN.

The instrument cluster receives odometer rolling count status from the PCM and stores the mileage in non-volatile memory (NVM). When the instrument cluster fails to receive the odometer rolling count status for more than 5 seconds, the odometer display shows dashes.

Tachometer
The instrument cluster receives tachometer information from the PCM over the communication network.

Fuel Gauge and Low Fuel Warning Indicator

NOTE: It is critical to follow the pinpoint test diagnostic methods to make sure the correct mode is being used during diagnostics.

The instrument cluster receives the fuel level signal from the fuel level sensor, part of the fuel pump module. The fuel level sensor measures variable resistance in the fuel tank depending on the current fuel level. When the fuel level is low, the resistance in the unit is low (15 ohms ± 2 ohms). When the fuel level is high, the resistance in the unit is high (160 ohms ± 4 ohms).

The instrument cluster uses 4 different operating modes to calculate the fuel level:
- anti-slosh (default mode)
- key OFF fueling
- key ON fueling
- recovery

After a fuel fill up, the time for the fuel gauge to move from empty (E) to full (F) ranges from 2 seconds to 55 minutes depending on which operating mode the fuel gauge is in.

The default fuel gauge mode is called the anti-slosh mode. To prevent fuel gauge changes from fuel slosh (gauge instability due to changes in fuel sender readings caused by fuel moving around in the tank), the fuel gauge takes approximately 55 minutes to go from full (F) to empty (E).

The key OFF fueling mode (2 seconds to read empty [E] to full [F]) requires 3 conditions be met:
- The key must be in the OFF position when refueling the vehicle.
- At least 15 percent of the vehicle's fuel capacity must be added to the fuel tank.
- The instrument cluster must receive a valid key ON fuel sender reading within 1 second of the key being put into the RUN position. The key ON sample readings are considered valid if the fuel sender reading is between 15 ohms ± 2 ohms and 160 ohms ± 4 ohms. If these conditions are not met, the fuel gauge stays in the anti-slosh mode, which results in a slow to read full (F) event.

The key ON fueling mode (approximately 90 seconds to read empty [E] to full [F]) requires 3 conditions be met:
- The transmission is in park (P).
- The key is in the RUN position.
- At least 15 percent of the vehicle's fuel capacity must be added to the fuel tank.

In key ON fueling mode, a 30 second timer activates after the transmission is put into the park (P) position. When the 30 second time has elapsed and at least 15 percent of the vehicle's fuel capacity has been added, the fuel gauge response time is 90 seconds to read from empty (E) to full (F). When the transmission is shifted out of park (P), the fuel gauge strategy reverts to the anti-slosh mode. This mode prevents slow to read full events from happening if the customer refuels the vehicle with the key in the RUN position.

Recovery mode is incorporated into the instrument cluster strategy to recover from a missing fuel level message during a refueling event. Missing fuel level messages result from intermittent opens in the fuel sender or its circuits. Recovery mode (empty [E] to full [F] approximately 20 minutes) is initiated when the following 2 conditions are met:
- The instrument cluster is in the anti-slosh (default) mode.
- The actual fuel level in the tank is greater than what is being displayed by the fuel gauge.

When the fuel gauge reads approximately 1/16th tank, the instrument cluster illuminates the low fuel warning indicator.

Battery Voltage Gauge and Charging System Warning Indicator
The instrument cluster measures system voltage and indicates whether the electrical system is operating at normal voltages. When the system voltage is too high, or too low, the PCM sends a message over the communication network to the instrument cluster to illuminate the charging system warning indicator.

Oil Pressure Gauge
The instrument cluster sends a signal voltage to the normally open oil pressure switch. When oil pressure is detected, the switch closes, grounding the circuit and causing the oil pressure gauge to display normal oil pressure.

Engine Coolant Temperature Gauge
The instrument cluster receives information on the engine coolant temperature from the PCM over the communication network. When the engine coolant temperature is within normal operating range, the gauge needle is in the normal range.

Safety Belt Warning Indicator
The driver safety belt switch is hardwired to the instrument cluster. When the safety belt is engaged, the driver safety belt switch grounds the circuit, causing the indicator to turn off. When the safety belt is unbuckled, the ground is removed and the instrument cluster illuminates the safety belt warning indicator.

Brake Warning Indicator
The brake warning indicator receives its signals from:
- the parking brake switch provides a ground when the parking brake is engaged.

- NOTE: The brake fluid level switch is part of the master cylinder and is not serviced separately.

the brake fluid level switch provides a ground when the brake fluid level is low or an open circuit if the brake fluid level switch is disconnected.

- the anti-lock brake system (ABS) module when the ABS module detects a base brake system concern.

Anti-Lock Brake System (ABS) Warning Indicator
The instrument cluster receives status information from the ABS module through a hardwired circuit from the ABS module. During normal operation, the ABS module supplies a ground to the ABS warning LED circuit, shutting the LED off. If the ABS module detects a fault, or if the ABS module is disconnected, ground is removed from the circuit, causing the ABS warning indicator to illuminate.

Air Bag Warning Indicator
The air bag warning indicator circuit is grounded by the restraint control module (RCM), through a hardwired circuit, when the RCM detects a fault in the air bag system. In addition, the RCM connector contains a shorting bar that grounds the circuit when the connector is disconnected. Failure of the air bag warning indicator to prove out once the ignition switch is turned to the RUN position indicates a fault in the air bag system.

Malfunction Indicator Lamp (MIL)
When there is a fault in the engine control system, the PCM sends a message over the communication network to the instrument cluster, to illuminate the MIL.

Check Fuel Cap Warning Indicator
When the PCM detects leaks in the evaporative emissions (EVAP) system that could be the result of a loose fuel filler cap, the PCM sends a message over the communication network to the instrument cluster, illuminating the check fuel cap warning indicator.

High Beam Indicator
The high beam indicator illuminates when the multifunction switch is in the high beam position and sends a voltage signal to the instrument cluster.

Right and Left Turn Indicator
The right and left turn indicators illuminate when the multifunction switch is in either turn signal position (or the hazard lamps position) and sends a voltage signal to the instrument cluster.

Wait to Start Indicator (diesel only)
The PCM provides the ground for the wait to start indicator. The glow plugs and the wait to start indicator operate at the same time. The indicator illuminates until the PCM has provided time for the glow plugs to heat the combustion chamber. The PCM then sends a message over the communication network to the instrument cluster to turn off the indicator.

Water-in-Fuel Indicator (diesel only)
The PCM receives a ground signal when water is sensed in the fuel. The PCM sends a message over the communication network to the instrument cluster, to illuminate the water-in-fuel indicator.

Check Gauge Warning Indicator
The check gauge warning indicator illuminates when a low oil pressure or an engine over temperature condition exists.

Electronic Throttle Control (ETC) Indicator
The PCM monitors the ETC system and provides the instrument cluster with the ETC status over the communication network. When a system concern is detected, the PCM provides the instrument cluster with a signal commanding the instrument cluster to turn the ETC indicator on.

AdvanceTrac(R) with Roll Stability Control (RSC) Indicator
The AdvanceTrac(R) with RSC indicator flashes when the vehicle RSC is in active mode or is being controlled by the ABS module. The instrument cluster receives the AdvanceTrac� with RSC signal from the ABS module through the communication network. The instrument cluster monitors the signal and when the ABS module detects a RSC concern, the instrument cluster illuminates the AdvanceTrac(R) with RSC indicator.