Principles of Operation

PRINCIPLES OF OPERATION

When installing a new instrument cluster, it is necessary to upload the module configuration information to the scan tool. Following installation of the instrument cluster, download the module configuration information from the scan tool into the new instrument cluster. Refer to Information Bus (Module Communications Network).

The following items are configurable:
- Speedometer calibration
- Brake system (base, anti-lock brake system (ABS), ABS/traction control [TC])
- Door ajar
- Shift indicator lamp
- Daytime running lamps (DRL)
- Door ajar warning chime
- Overspeed warning chime
- Back-up warning chime
- Key in warning chime
- Security system

The instrument cluster receives the information over the controller area network (CAN) circuits. The instrument cluster carries out a display prove-out to verify that the warning/indicator lamps and monitored systems are operating correctly. When the ignition switch is turned to the ON position, the charging system warning indicator, the low oil pressure warning indicator, and the malfunction indicator lamp (MIL) illuminate until the engine is started and operating normally. The safety belt warning indicator proves out for 65 seconds or until the safety belt is fastened.

Each time the ignition switch is turned from the OFF to the ON positions, the following instrument cluster warning indicators prove out for 3 seconds:
- ABS warning indicator
- Air bag warning indicator (6 seconds)
- BRAKE warning indicator
- Fail safe cooling warning indicator
- Low fuel warning indicator
- Traction control indicator
- Anti-theft indicator
- Check fuel cap warning indicator
- Wrench warning indicator
- Tire pressure monitoring system (TPMS) warning indicator

Instrument Cluster Gauges

Tachometer
The instrument cluster receives the tachometer data from the powertrain control module (PCM) over the communication network and commands the tachometer pointer between 0 and 7,000 rpm (4.0L engines), or between 0 and 8,000 rpm (4.6L engines) according to the data.

Speedometer
The instrument cluster receives the vehicle speed information from the PCM over the communication network and displays it on the speedometer gauge. If the instrument cluster receives no vehicle speed signal after 1 second, the speedometer defaults to 0.

Odometer
The instrument cluster receives an odometer message from the PCM and stores the mileage in memory. When the instrument cluster fails to receive the odometer message for more than 2 seconds, the odometer displays dashes.

Fuel Gauge
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:
- Key OFF fueling
- Anti-slosh (default mode)
- 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 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 throughout the entire refueling of the vehicle.
- At least 15% 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 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 empty (E) to full (F).

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) (automatic transmissions), or the parking brake applied (manual transmissions).
- The key is in the RUN position.
- At least 15% 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 (automatic transmissions) or when the parking brake is applied (manual transmissions). When the 30 second time has elapsed and at least 15% 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) or the parking brake is released, the fuel gauge strategy reverts to the anti-slosh mode. The key ON fueling 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 missing fuel level inputs during a refueling event. Missing fuel level input 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.

Engine Coolant Temperature Gauge
The PCM receives the engine coolant temperature status through hardwired circuitry to the engine coolant temperature (ECT) sensor. The instrument cluster receives the engine coolant temperature data from the PCM over the communication network. The instrument cluster monitors the engine coolant temperature data received from the PCM and commands the engine coolant temperature gauge pointer.

Voltage Gauge
The voltage gauge displays the system battery voltage as measured at the instrument cluster run input circuit.

Oil Pressure Gauge
The smart junction box (SJB) is hardwired to the oil pressure switch. The oil pressure switch unit consists of a diaphragm and contact points, which are normally open. When there is low (under 41 kPa [6 psi]) or no oil pressure, the oil pressure switch remains open, removing the ground to the SJB. When sufficient oil pressure exists, the oil pressure switch closes providing a ground signal to the SJB. The SJB monitors the oil pressure ground signal and sends a message to the instrument cluster to operate the oil pressure gauge according to the engine oil pressure.

Boost Gauge (GT 500 Only)
The boost gauge measures the amount of engine boost provided by the supercharger in pounds per square inch (PSI). The instrument cluster receives the boost gauge data from the powertrain control module (PCM) over the high speed controller area network (CAN) communication bus lines.

Indicators

Low Fuel Warning Indicator
The low fuel warning indicator is controlled by the instrument cluster and warns the driver when the fuel level is 1/16 of a tank or lower.

Check Fuel Cap Warning Indicator
The PCM monitors pressure in the fuel evaporative system and detects massive or critical losses of pressure. When a critical loss of pressure in the fuel evaporative system is detected, the PCM provides a message over the communication network and the instrument cluster illuminates the check fuel cap warning indicator.

BRAKE Warning Indicator
The brake warning indicator alerts the driver if any of the following brake system conditions are present: the parking brake is set, the brake fluid level is low, the ABS module detects a base brake system failure, there is a loss of communication between the instrument cluster and the SJB, or there is a loss of communication between the instrument cluster and the ABS module.

Safety Belt Warning Indicator
The safety belt warning indicator informs the driver that his/her safety belt and/or the front passengers safety belt is unbuckled. The first 65 seconds after the ignition switch transitions from OFF or ACC to RUN or START, the safety belt warning indicator and the associated chime are used as a reminder to the driver that the front row safety belts are not buckled. In this first 65 seconds the indicator illuminates when the driver and/or front passenger safety belt is unbuckled (with a person in the seat) and turns off whenever the safety belt(s) in the occupied front row seat(s) is buckled. The indicator illuminates again if a safety belt is unbuckled after both are buckled and the 65 seconds has not yet expired. After 65 seconds, the indicator turns off regardless of the front row safety belts status.

Anti-Lock Brake System (ABS) Warning Indicator
The ABS warning indicator informs the driver of a malfunction in the ABS system. Inputs are provided by the ABS module over the communication network.

Malfunction Indicator Lamp (MIL)
The MIL is illuminated when a DTC is detected by the PCM. The instrument cluster receives the MIL data from the PCM through the communication network.

Wrench Warning Indicator
The PCM monitors the electronic throttle control (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 illuminate the wrench indicator or display a message if equipped with a message center.

High Beam Indicator
When the high beams are turned on, the SJB sends a signal to the instrument cluster through the communication network to illuminate the high beam indicator.

Turn Indicators
The SJB sends a message to the instrument cluster over the communication network when the multifunction switch is in the RH and LH turn signal position. When the multifunction switch is in the RH or LH turn signal position, the instrument cluster flashes the RH or LH turn indicators.

Air Bag Warning Indicator
The air bag warning indicator is used to provide a status of the supplemental restraint system. The instrument cluster receives a message from the restraint control module (RCM) over the hard wired circuits. If an air bag system concern is detected, a DTC is logged and the RCM sends a message to the instrument cluster to illuminate the air bag warning indicator.

Speed Control Indicator
The instrument cluster receives the speed control data from the PCM through the communication network. When the speed control is engaged, the PCM provides a signal to the instrument cluster to illuminate the speed control indicator.

Charging System Warning Indicator
The PCM constantly monitors the generator regulator output. When the PCM detects a continuous high or low output signal, or when the ignition switch is ON and the engine is OFF, the PCM sends a message over the communication network to the instrument cluster to illuminate the charging system warning indicator. When the ignition switch is in the ON position, with the engine running, and the PCM determines that the set point for the regulator has been met, the PCM sends a message to the instrument cluster to turn off the charging system warning indicator.

Failsafe Cooling Warning Indicator
The failsafe cooling warning indicator informs the driver the engine coolant is overheating due to loss of engine coolant fluid or other cause, and the PCM is taking on limp home strategy. The other purpose is to inform the driver the engine cannot be cooled enough with the limp home strategy and the engine is about to be shut down by the PCM. The failsafe cooling information is sent from the PCM to the instrument cluster to illuminate the failsafe cooling warning indicator.

Overdrive Off (O/D OFF) Indicator
The instrument cluster receives the overdrive off signal from the PCM through the communication network. When the transmission overdrive is selected off, the overdrive off switch provides a ground signal to the PCM. The PCM, upon receipt of the overdrive off ground signal, provides an overdrive off signal to the instrument cluster and the instrument cluster illuminates the overdrive off indicator.

Daytime Running Lamp (DRL) Indicator
When the DRL is on, the SJB sends a message over the communication network, to the instrument cluster, illuminating the DRL indicator.

Low Oil Pressure Warning Indicator
The SJB is hardwired to the oil pressure switch. The oil pressure switch unit consists of a diaphragm and contact points, which are normally open. When there is low (under 41 kPa [6 psi]) or no oil pressure, the oil pressure switch remains open, removing the ground to the SJB. When sufficient oil pressure exists, the oil pressure switch closes, providing a ground signal to the SJB. The SJB monitors the oil pressure ground signal and sends a message to the instrument cluster to turn the indicator on or off according to the engine oil pressure.

Door/Trunk Ajar Warning Indicator
The door ajar indicator informs the driver that one or more doors, or the decklid is open while the ignition switch is in the RUN position. When a door or decklid is ajar, the SJB sends a message to the instrument cluster to illuminate the door ajar indicator.

Traction Control Indicator
The traction control indicator flashes when the vehicle traction control is in active mode or is being controlled by the ABS module. The instrument cluster receives the traction control signal from the ABS module through the communication network. The instrument cluster monitors the traction control signal, and when the ABS module detects a traction control concern, the instrument cluster illuminates the traction control indicator.

Anti-Theft Indicator
The anti-theft indicator is used to deter potential thefts of the vehicle by providing a conspicuous indicator that flashes every 2 seconds with the ignition off when the passive anti-theft system (PATS) is armed. The instrument cluster receives the anti-theft status from the PCM over the high speed CAN communication bus lines.

Shift Indicator (GT 500 Only)
The shift indicator is used to inform the driver of shift points that provide the highest fuel economy. The PCM uses engine throttle position, engine load and engine rpm information to determine what the optimum shift point is to provide the greatest fuel economy.

Performance Shift Warning Indicator (GT 500 Only)
The performance shift warning indicator shares the SVT logo on the tachometer. The performance shift indicator is configurable on or off and uses engine rpm to determine when to illuminate. The SVT logo is normally backlight in red when the performance indicator is configured off. When the performance shift warning indicator is configured on, the SVT logo red backlighting is turned off. When a preset engine rpm is reached, the SVT logo illuminates orange to alert the driver of the selected shift point. The performance shift warning indicator can be configured on or off through the message center. Refer to Driver/Vehicle Information Display, Message Center Configuration.

Tire Pressure Monitoring System (TPMS) Warning Indicator
The tire pressure warning indicator alerts the driver that one or more of the tires on the vehicle has low tire pressure or is flat. The tire pressure monitoring system (TPMS) system consists of a tire pressure sensor and a transmitter located on each tire. The SJB receives the data from each tire and transmits the status over the medium speed CAN communication bus lines to the instrument cluster to indicate whether the low tire pressure warning indicator telltale should be illuminated, flashed, or turned off.