Principles of Operation
PRINCIPLES OF OPERATIONNOTE: When installing a new instrument cluster, it is necessary to upload the module configuration to the scan tool. Following installation of the instrument cluster, download the module configuration from the scan tool into the new instrument cluster. Refer to Information Bus (Module Communications Network) to carry out programmable module installation (PMI). Programming and Relearning
The instrument cluster gauges are not installed separately from the instrument cluster. 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.
The instrument cluster is a hybrid electronic cluster (HEC) that uses a microprocessor to control the gauge and indicator functions. The instrument cluster receives its inputs from modules and components through hardwired circuitry and the high speed controller area network (HS-CAN) bus. The instrument cluster uses each input to control an output through the gauges and indicators.
Instrument Cluster Gateway Function
The instrument cluster acts as a gateway module by receiving information in one format and transmitting it to other modules using another format. For example, the instrument cluster receives the vehicle speed data from the PCM over the high speed controller area network (HS-CAN), converts the data into a MS-CAN message and sends (gateways) the message to other network modules such as the vehicle security module. This enables network communication between modules that do not communicate using the same network (HS-CAN or the MS-CAN).
Instrument Cluster Messages
NOTE: Whenever a message is suspected as missing and confirmed by a missing message DTC (U-code), it is important to look for other symptoms that may also be present in the instrument cluster and throughout the vehicle. Once a DTC is set in the instrument cluster it may be helpful to review the complete message list available Information Bus (Module Communications Network) to see what other modules also rely on the same message and run the self-test for those modules. If the message is missing from other modules, the same DTC may also be set in those modules. Confirmation of missing messages common to multiple modules may indicate that the originating module is the source of the concern or the communication network may be experiencing some problems.
The instrument cluster uses input messages from other modules to control some of the gauges and indicators over the communication networks. If a required message is missing or invalid for less than 5 seconds, the gauge or indicator that requires the message remains at the last commanded state based upon the last known good message. For example, if the engine rpm data is missing for less than 5 seconds and the engine was running at 1,000 rpm, the tachometer remains at 1,000 rpm until the next valid message is received. If the message remains missing or invalid for greater than 5 seconds, the instrument cluster sets a U-code DTC and the output becomes a default action for the indicator or gauge. Each indicator or gauge utilizes a different default strategy depending on the nature of the indication. In the example above, the tachometer defaults to 0 rpm. If the messaged input to the cluster returns at any time, the normal function of the gauge or indicator resumes.
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 CAN circuits to another module.
- which module controls the output of the feature.
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: On gasoline-equipped vehicles, the fuel pump module may also be called the fuel tank unit and on diesel-equipped vehicles, the fuel level sender may also be called the fuel level sensor or fuel gauge sensor.
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 empty (E) to full (F).
The key OFF fueling mode (2 seconds to read empty)
- 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 key ON fueling mode (approximately 90 seconds to read empty
- The transmission is in PARK (P).
- 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. 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), 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 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
- 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 of a 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 unbuckled, the driver safety belt switch grounds the circuit and the instrument cluster illuminates the safety belt warning indicator. When the safety belt is engaged, the ground is removed, causing the lamp to turn off.
Brake Warning Indicator
The brake warning indicator receives its signals from the parking brake switch and brake fluid level switch as follows:
- the parking brake switch provides a ground when the parking brake is engaged.
- the brake fluid level switch provides a ground when the brake fluid level is low, an open circuit is detected or if the brake fluid level switch is disconnected.
Anti-Lock Brake System (ABS) Warning Indicator
On vehicles equipped with traction control/stability assist, the instrument cluster receives the ABS status from the ABS module over the communication network. When the ABS concern is present, the ABS module sends a message to the instrument cluster to turn on the ABS warning indicator.
On vehicles not equipped with traction control/stability assist, the instrument cluster receives status information from the ABS module through hardwired circuitry. 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 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 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 instrument cluster receives the wait to start status from the PCM over the communication network. 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.
Engine Over Temperature Warning Indicator
The PCM receives the engine coolant temperature status through hardwired circuitry from the ECT sensor (6.0L diesel engine), and from the cylinder head temperature (CHT) sensor (4.6L, 5.4L and 6.8L engines). The instrument cluster receives the engine coolant temperature data from the PCM over the high speed CAN. The instrument cluster monitors the engine coolant temperature data received from the PCM and when the engine coolant temperature is high, the engine over temperature warning indicator illuminates.
Wrench Warning Indicator
The PCM monitors the electronic throttle control system and provides the instrument cluster with the electronic throttle control 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 wrench warning indicator on.
Traction Control/Stability Assist Indicator
The traction control/stability assist indicator flashes when the vehicle traction control or stability assist system is in active mode or is being controlled by the anti-lock brake system (ABS) module. The instrument cluster receives the traction control/stability assist signal from the ABS module through the communication network. The instrument cluster monitors the traction control/stability assist signal and, when the ABS module detects a concern, the instrument cluster illuminates the traction control/stability assist indicator.
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.
Speed Control Indicator
The instrument cluster receives the speed control data from the PCM over the high speed CAN. When the speed control is engaged, the PCM provides a signal to the instrument cluster to illuminate the speed control indicator.
O/D OFF Indicator (If Equipped)
The instrument cluster receives the overdrive off signal from the PCM over the high speed CAN. The overdrive off switch is hardwired to the PCM. When the transmission overdrive is turned 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 message to the instrument cluster to turn on the O/D OFF indicator.
Tow Haul Indicator (If Equipped)
The instrument cluster receives the tow haul signal from the PCM over the high speed CAN. The tow haul switch is hardwired to the PCM. When the tow haul is selected, the tow haul switch provides a ground signal to the PCM. The PCM, upon receipt of the tow haul ground signal, provides a tow haul message to the instrument cluster to turn on the tow haul indicator.