Principles of Operation

PRINCIPLES OF OPERATION

When installing a new instrument cluster, it is necessary to upload the module configuration information to the diagnostic tool. Following installation of the instrument cluster, download the module configuration information from the diagnostic tool into the new instrument cluster.
The following items are configurable:
- gulf coast countries (GCC) destination
- traction control
- oil life threshold
- oil minder off
- powertrain control module (PCM) oil life used
- engine idle hour meter
- back up aid
- air suspension

The message center instrument cluster is a configurable, hybrid electronic cluster (HEC) that contains a microprocessor, gauges, indicator lamps, and internal circuitry. The instrument cluster uses hardwired circuitry, the standard corporate protocol (SCP), and the controller area network (CAN) to transmit and receive data from other modules.It is very important to understand:
- where the input originates.
- all the information necessary in order for a feature to operate.
- which module(s) receive(s) the input or command message.
- whether the module which received the input controls the output of the feature, or whether it outputs a message over the SCP or the CAN circuits to another module.
- which module controls the output of the feature.

The instrument cluster carries out a display prove-out to verify that the warning/indicator lamps and monitored systems are operating correctly. The safety belt warning indicator illuminates for 65 seconds ± 1 second or until the safety belt is fastened. 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. 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:
- air bag (6 seconds on, 2 seconds off)
- ABS
- BRAKE
- traction control

Gauges

Fuel Gauge
The instrument cluster receives the fuel level signal from the fuel level sensor, which is part of the fuel pump module. The fuel level sensor changes resistance as the fuel level changes in the fuel tank. When the fuel level is dry (empty), the resistance is low (15 ohms ± 2 ohms). When the fuel level is full, the resistance is high (160 ohms ± 4 ohms). The instrument cluster has 4 operating modes, 2 of which are most commonly used. It is critical to follow the pinpoint test diagnostic methods which identify the correct mode is being used during diagnostics. The default mode is called the slosh mode. In this mode the instrument cluster fuel gauge pointer takes approximately 55 minutes to go from full (F) to empty (E), or from empty (E) to full (F). The other mode is called the fast acquire mode. The fast acquire mode operates when 2 valid fuel sender readings (1 key OFF, 1 key ON) show a 15 percent or greater change in the fuel tank level. In this mode the instrument cluster fuel gauge pointer takes approximately 2 seconds to go from full (F) to empty (E), or from empty (E) to full (F). To get the fuel gauge into fast acquire mode the following conditions must be met:
- Twenty seconds after the ignition switch is turned to the OFF position, the instrument cluster takes a key OFF reading of the fuel sender, and stores this value in memory.
- When the ignition switch is turned to the RUN position, the instrument cluster takes another reading of the fuel sender. This reading is called the key ON sample.

The instrument cluster determines if the key OFF and key ON readings are good. If the 2 readings differ by 15 percent or more of the fuel capacity then the fuel gauge goes into the fast acquire mode.

Engine Coolant Temperature Gauge
The PCM receives the engine coolant temperature status through hardwired circuitry from the cylinder head temperature sensor. The instrument cluster receives the engine coolant temperature data from the PCM over the CAN. The instrument cluster monitors the engine coolant temperature data received from the PCM and commands the engine coolant temperature gauge pointer.

Tachometer
The tachometer is electrically operated and indicates the engine speed in revolutions per minute (rpm). The tachometer range is 0 to 7,000 rpm. The PCM uses the crankshaft position sensor to measure the engine rpm and sends the data to the instrument cluster, over the CAN, to command the tachometer gauge. If the rpm information sent to the instrument cluster is invalid or missing, the instrument cluster defaults the tachometer to 0 rpm.

Speedometer
The instrument cluster receives the vehicle speed sensor (VSS) signal from the PCM over the CAN. The instrument cluster monitors the VSS input from the PCM and commands the speedometer with a corresponding movement of the pointer.

Indicators

Charging System Warning Indicator
The instrument cluster receives the charging system status from the PCM over the communication network. Charging system data is monitored by the instrument cluster and when the charging system voltage is low, illuminates the charging system warning indicator.

BRAKE Warning Indicator
The parking brake switch and the brake fluid level switch (part of the master cylinder) are hardwired to the instrument cluster. The BRAKE warning indicator uses 3 inputs. The first input is provided by the parking brake switch, and when applied, provides a ground signal to the instrument cluster, illuminating the BRAKE warning indicator. The second input is controlled by the brake fluid level switch. When the brake fluid level is low, the brake fluid level switch closes and provides a ground to the instrument cluster to illuminate the BRAKE warning indicator. The third input uses the base brake system. If a base brake system concern occurs, the anti-lock brake system (ABS) module provides a brake signal to the instrument cluster over the CAN, to illuminate the BRAKE warning indicator. If a loss of communication from the ABS module to the instrument cluster occurs, the BRAKE warning indicator illuminates.

Anti-lock Brake System (ABS) Warning Indicator
The ABS warning indicator is used to indicate an ABS concern or deactivation of the ABS. The instrument cluster, upon receipt of the ABS message from the ABS module over the CAN, turns on the ABS warning indicator.

Malfunction Indicator Lamp (MIL)
The MIL informs the driver of a malfunction in the powertrain that affects the vehicle emissions system. The MIL is illuminated when a fault condition is detected by the PCM and a diagnostic trouble code (DTC) has been set. The instrument cluster receives the MIL data from the PCM over the CAN.

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 CAN. If an air bag system concern is detected, a diagnostic trouble code (DTC) is logged and the RCM sends a message to the instrument cluster to illuminate the air bag warning indicator.

Safety Belt Warning Indicator
The safety belt switches are hardwired to the RCM and the RCM monitors the safety belt switch position. The RCM communicates the safety belt information to the LCM over the SCP which is then relayed to the instrument cluster over the SCP network to turn on or off the safety belt warning indicator according to the safety belt switch position.

Low Oil Pressure Warning Indicator
The instrument cluster 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 or no oil pressure, the oil pressure switch remains open, removing the ground to the instrument cluster. When sufficient oil pressure exists, the oil pressure switch closes, providing a ground signal to the instrument cluster to turn the indicator on or off according to the engine oil pressure.

Turn Signal Indicators
When the multifunction switch is in the LH turn signal position or the RH turn signal position, voltage is sent from the multifunction switch to the instrument cluster through hardwired circuitry. The instrument cluster flashes on and off the LH or RH turn signal indicators.

High Beam Indicator
When the high beams are turned on, the lighting control module (LCM) sends a signal to the instrument cluster over the SCP communication network to illuminate the high beam indicator.

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

Traction Control Indicator
The traction control indicator informs the driver that a traction control event is taking place, by flashing the traction control indicator during the event. The traction control indicator illuminates constantly when a malfunction is detected in the traction control system, or if the traction control system is disabled by the operator. The traction control is controlled by the ABS module over the CAN.

Engine Idle Hour Meter (Limousine)
The instrument cluster receives the digital transmission range (TR) sensor status message from the PCM over the high speed CAN, and if the engine speed is greater than 400 rpm, it records the amount of time the engine runs with the transmission in PARK or NEUTRAL.