Principles of Operation

PRINCIPLES OF OPERATION

The base and message center instrument clusters are configurable, electronic clusters that contain a microprocessor, gauges, indicator lamps, and internal circuitry. The instrument cluster uses the controller area network (CAN) to transmit and receive data from other modules.

The instrument cluster has many items that can be configured to be enabled or disabled. When installing a new instrument cluster, it is necessary to upload the module configuration information to the scan tool. Following the installation of the new instrument cluster, the module configuration must be downloaded from the scan tool into the new instrument cluster. Refer to Information Bus (Module Communications Network).

The following items in the instrument cluster are configurable:
- Engineering test mode (ETM) enabled
- English/metric
- Overspeed chime enabled
- Traction control (TC) present
- Anti-lock brake system (ABS) present
- Electronic automatic temperature control (EATC) present
- Manual transaxle
- Integrated key transmitter (IKT) feature
- Lamp outage enabled (message center instrument cluster only)
- Easy exit enabled (message center instrument cluster only)
- Reverse mirror enabled (message center instrument cluster only)
- White backlighting
- 25-step backlighting
- Failsafe cooling enabled
- Speed tolerance
- Default language

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.
- does the module which received the input control the output of the feature, or does it output a message over the communication network 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 70 seconds or until the safety belt is fastened. When the ignition switch is turned to the ON position, the charging system warning indicator, the malfunction indicator lamp (MIL) and the low oil pressure warning indicator 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:
- ABS warning indicator
- Air bag warning indicator (6 seconds)
- BRAKE warning indicator
- Low fuel warning indicator (if equipped)
- Traction assist indicator
- Passive anti-theft system (PATS) warning indicator
- Check fuel cap warning indicator
- Powertrain malfunction (wrench) warning indicator

Gauges

Integrated Circuit Display
The integrated circuit display is a vacuum fluorescent display that contains the odometer, trip odometer, and compass display on base clusters and the message center display on message center clusters. The compass module is hardwired to the instrument cluster. The odometer information is transmitted from the powertrain control module (PCM) over the communication network to the instrument cluster. The instrument cluster displays the appropriate message(s) upon receipt of the compass heading and odometer data received.

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

Odometer
The odometer and trip odometer are viewed through the message center display on message center clusters or in the integrated circuit display on base clusters. The odometer is tamper resistant and accumulates and registers up to 1 million kilometers in metric mode or 1 million miles in English mode, based upon rolling count data sent from the PCM over the communication network. The trip odometer is resettable and accumulates and registers up to 1,000 kilometers or 1,000 miles.

Fuel Gauge

NOTE:
- The fuel pump module may also be called the fuel tank unit.
- The remote fuel level sender may also be called the fuel level sensor.

On front wheel drive (FWD) vehicles, 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 high (180 ohms ± 4 ohms). When the fuel level is high, the resistance in the unit is low (10 ohms ± 2 ohms).

On all wheel drive (AWD) vehicles, the fuel tank is a saddle tank design with 2 variable resistance senders, driven by floats, that provide resistances related to fuel height, in each side, to the cluster through hardwired inputs. The fuel level is read from each fuel sender through a 2-wire input. The fuel senders provide variable resistance between 180 ohms ± 4 ohms (empty tank) and 10 ohms ± 2 ohms (full tank). If the fuel level is low, the resistance in the fuel level sensor is high, causing the gauge to indicate empty (E). When the fuel level is high, the resistance in the fuel level sensor is low, and the gauge indicates full (F).

As fuel is consumed from the fuel pump module side of the fuel tank (the side with the fuel filler hose inlet), fuel is transferred from the secondary fuel level sender side of the tank (the side opposite the fuel filler hose inlet) to the fuel pump module side of the tank. The fuel pump module is connected to the secondary fuel level sender by a crossover line and transfers fuel when the fuel pump module is running.

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 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 [E] to full [F]) requires 3 conditions be met:
- The key must be in the OFF position during 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 10 ohms ± 2 ohms and 180 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 transaxle is in PARK (P) (automatic transaxle), or the parking brake is applied (manual transaxle).
- 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 transaxle is put into the PARK (P) position (automatic transaxle) or when the parking brake is applied (manual transaxle). 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 transaxle 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 a missing fuel level input during a refueling event. Missing fuel level inputs 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 temperature gauge indication with a corresponding movement of the pointer.

Tachometer
The PCM uses the crankshaft position sensor to measure the engine rpm and sends the data to the instrument cluster, over the communication network, to command the tachometer gauge.

Indicators

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

BRAKE Warning Indicator

NOTE: When the anti-lock brake system (ABS) module detects an electronic brake distribution (EBD) fault, the ABS module sends a message to the instrument cluster. Whenever the instrument cluster receives an EBD message from the ABS module, the instrument cluster illuminates both the brake warning indicator and the ABS warning indicator simultaneously.

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 smart junction box (SJB), or there is a loss of communication between the instrument cluster and the ABS module. If the brake system experiences an EBD failure, both the BRAKE warning indicator and the ABS warning indicator illuminate.

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. Refer to Antilock Brakes/Traction Control Systems. If the brake system experiences an EBD failure, both the BRAKE warning indicator and the ABS warning indicator illuminate.

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 DTC is detected by the PCM. The instrument cluster receives the MIL data from the PCM over the communication network.

Air Bag Warning Indicator
The air bag warning indicator is used to provide a status of the supplemental restraint system (SRS). The instrument cluster receives a message from the restraints control module (RCM) over the communication network. 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.

Safety Belt Warning Indicator
The safety belt warning indicator informs the driver that his or her safety belt and/or the front passenger's safety belt is unbuckled. During the first 70 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. During this first 70 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 70 seconds has not yet expired.

Low Fuel Warning Indicator (If Equipped)
The low fuel warning indicator is equipped on non-message center clusters. The low fuel warning indicator is controlled by the instrument cluster and uses hardwired fuel level data from the fuel pump gauge sender. When the fuel level drops below approximately 1/8 of a tank, the instrument cluster illuminates the low fuel warning indicator.

Low Oil Pressure Warning Indicator
The SJB is hardwired to the oil pressure switch. The oil pressure switch 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 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 Ajar 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 Assist Indicator
The traction assist indicator informs the driver that a traction assist event is taking place, by flashing the traction assist indicator during the event. The traction assist indicator illuminates constantly when a malfunction is detected in the traction assist system, or if the traction assist system is disabled by the operator. The traction assist indicator is controlled by the PCM over the communication network.

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

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

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

Wrench Warning Indicator
The PCM, the transmission control module (TCM) and the four wheel drive (4WD) control module (if equipped) monitor the powertrain system and provide the instrument cluster with the operating status over the communication network. When a system concern is detected, the PCM, the TCM or the 4WD control module provide the instrument cluster with a signal commanding the instrument cluster to illuminate the wrench warning indicator.

Check Fuel Cap Warning Indicator
The PCM monitors pressure in the fuel evaporative system and detects 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.

Passive Anti-Theft System (PATS) Warning Indicator
The PATS transceiver is hardwired to the instrument cluster. When the key is placed into the ignition lock cylinder, and turned to the ON or START position, the PATS transceiver reads the electronic code stored in the ignition key, and transmits this code to the instrument cluster. If the electronic code is correct, the instrument cluster transmits the key status over the communication network to the PCM to enable the starter relay, the fuel pump, and the fuel injectors. If a theft is detected, the instrument cluster flashes the PATS warning indicator or turns the PATS warning indicator steady.

O/D OFF Indicator (Late Build Fusion, Milan and MKZ Only)
The TCM monitors the overdrive (O/D) off switch status. When the O/D function is selected off, the TCM sends a message to the instrument cluster over the communication network to turn on the O/D OFF indicator.