Principles of Operation

PRINCIPLES OF OPERATION

The instrument cluster is a hybrid electronic instrument cluster (HEC). The instrument cluster and the smart junction box (SJB) use a combination of hardwired circuitry, the standard corporate protocol (SCP), and the controller area network (CAN) communication circuits to transmit and receive information. 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 communication network to another module.
- which module controls the output of the feature.

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). The following items are configurable:
- Safety belt minder
- Tire pressure monitoring system (TPMS) configuration
- Overspeed warning
- Enhanced door ajar warning display
- Overhead display
- Speedometer bias
- Default language
- Oil life
- Oil life status and warning

Each time the ignition switch is turned from the OFF to the ON position, the charging system indicator, the low oil pressure indicator and the malfunction indicator lamp (MIL) prove out and remain on until the engine is started and operating normally. The safety belt warning indicator proves out for 65 seconds, or turns off when the safety belt is buckled. The air bag indicator proves out for approximately 6-8 seconds while the following instrument cluster indicators and warning indicators prove out for approximately 3 seconds:
- ABS warning indicator
- Low tire pressure warning indicator
- Lamp out (base cluster only)
- Door ajar (base cluster only)
- Low fuel
- BRAKE system
- Traction control
- Check fuel cap
- Transaxle malfunction
- Low washer fluid level (base cluster only)
- Failsafe cooling warning indicator (base cluster only)
- Electric steering malfunction (base cluster only)

Instrument Cluster Gauges

Engine Coolant Temperature Gauge
The temperature gauge displays the engine coolant temperature (ECT), or the cylinder head temperature (CHT), received from the powertrain control module (PCM) over the communication network. The temperature gauge also indicates when failsafe cooling is active. It is a "flat response" gauge providing an indication of whether the engine is cold, normal, overheated, or in failsafe cooling mode. The input temperature and corresponding output gauge command are both filtered to smooth out the pointer movement.

Fuel Gauge

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 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 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 [E] to full [F]) requires 3 conditions be met:
- The transaxle 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 transaxle 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 transaxle 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 missing fuel level input after 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.

Speedometer
The instrument cluster receives the vehicle speed sensor (VSS) signal from the anti-lock brake system (ABS) module, over the communication network, and monitors the VSS input and commands the speedometer pointer.

Tachometer
The tachometer gauge displays the engine revolution speed accurately and responsively. The input to the instrument cluster is a communication message from the PCM. The tachometer gauge feature operates only when the ignition switch is in the RUN or START positions.

Instrument Cluster Indicators

Low Tire Pressure Warning Indicator
The low 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 TPMS consists of a tire pressure sensor and a transmitter located on each tire. The smart junction box (SJB) receives the data from each tire and transmits the data over the communication network to the instrument cluster to indicate whether the low tire pressure warning indicator telltale should be illuminated, flashed, or turned off.

Check Fuel Cap Indicator
The check fuel cap indicator is used to indicate significant leaks in the fuel tank evaporative system due to a loose fuel cap. Fuel tank pressure is monitored by the PCM. If a leak is detected, it signals a fault to the instrument cluster over the communication network. Once the PCM has detected a loose fuel cap and the check fuel cap indicator is illuminated, the check fuel cap indicator remains illuminated until the fuel cap is secured and the vehicle has been running for several minutes. Refer to Computers and Control Systems.

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

Air Bag Warning Indicator
The supplemental restraint system is monitored and controlled by the restraints control module (RCM). The status of the supplemental system is sent from the RCM to the instrument cluster through hardwired circuitry. The air bag warning indicator is illuminated if the RCM sends a ground signal to the instrument cluster.

ABS Warning Indicator
The ABS is monitored by the ABS module, which sends the status signal to the instrument cluster over the communication network. The instrument cluster uses this input to determine whether or not there is a fault with the ABS and illuminates the ABS warning indicator according to the input.

BRAKE Warning Indicator
The brake warning indicator supports 3 separate functions: base brake system failure, low brake fluid level, and engagement of the parking brake. These functions are controlled by the parking brake control switch, the brake fluid level switch and the brake system itself. The brake fluid level switch and the parking brake control switch are hardwired directly to the SJB. The status of both the brake fluid level and parking brake switches are sent from the SJB to the instrument cluster over circuits 1309 (RD/YE) and 1305 (DB). The base brake system status is monitored by the ABS module and sent to the instrument cluster over the communication network.

Charging System Warning Indicator
The charging system controls are accomplished through the PCM, which monitors the output of the generator through hardwired circuitry. The status of the charging system is then relayed from the PCM to the instrument cluster over the communication network.

Door Ajar Warning (Base Cluster Only)
The door ajar warning indicator feature informs the driver that any of the 4 doors or liftgate is open or not completely closed. The door ajar warning indicator information is delivered from the SJB to the instrument cluster 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 over the communication network.

Low Fuel Level Warning Indicator
The low fuel level warning indicator illuminates when the fuel level reaches a predetermined level of approximately 1/8 tank. The instrument cluster receives the fuel level information directly from the fuel sender.

Safety Belt Warning Indicator
The instrument cluster receives the safety belt warning status from the RCM over hardwired circuitry. The safety belt switch is hardwired to the RCM. When the safety belt is fastened, the safety belt switch opens and removes the ground to the RCM and turns off the indicator. When the safety belt is unfastened, the safety belt switch closes and grounds the circuit to the RCM and the indicator illuminates.

Low Oil Pressure Warning Indicator
The oil pressure switch is hardwired to the SJB. 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 sends a message to the instrument cluster over the communication network. The instrument cluster monitors the oil pressure ground signal and commands the low oil pressure warning indicator on or off according to engine oil pressure.

Check Transmission Warning Indicator
When the transaxle is malfunctioning the PCM sends the instrument cluster a message over the communication network to illuminate the indicator.

Speed Control Indicator
The speed control status is sent by the speed control activator to the instrument cluster over the communication network. The speed control indicator illuminates when the speed control is set.

High Beam Indicator
The instrument cluster provides a ground for the high beam indicator. When the high beams are turned on, the multifunction switch provides a voltage signal to the instrument cluster through hardwired circuitry and illuminates the high beam indicator.

LH and RH Turn Signal Indicators
The instrument cluster provides a ground for the RH and LH turn indicators. When the multifunction switch is in the RH or LH TURN position, voltage is supplied to the instrument cluster through hardwired circuitry and the RH or LH turn indicators flash on and off.

Lamp Out Indicator (Base Cluster Only)
The lamp out information is delivered from the SJB to the instrument cluster over the communication network. The purpose of this indicator is to inform the driver that 1 or more of the exterior lamps are inoperative.

Low Washer Fluid Warning Indicator (Base Cluster Only)
The SJB is hardwired to the low washer fluid switch. The low washer fluid switch closes and provides a ground to the SJB when the washer fluid is low. The SJB sends the instrument cluster a message over the communication network. When the washer fluid is below the low level, the low washer fluid switch closes and supplies the ground to the SJB and the low washer fluid warning indicator illuminates. When the washer fluid is above the low level, the low washer fluid switch opens and removes the ground to the SJB and the low washer fluid warning indicator turns off.

Failsafe Cooling Warning Indicator (Base Cluster Only)
The failsafe cooling warning indicator informs the driver the engine 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 indicator information is delivered from the PCM to the instrument cluster over the communication network.