Instrument Cluster

INSTRUMENT CLUSTER
The instrument cluster used in the Jeep Wrangler contains six gauges and eleven warning lamps. The gauges are positioned with information received by the cluster over the CCD bus from the PCM. Some of the lamps are hardwired and some are controlled by the cluster using CCD bus information. The vehicle chime function is contained on the cluster circuit board as well as the timer for the rear window defogger. There is a self test available for the cluster that will actuate all the gauges and place them at their calibration points. The test will not run if the cluster sees engine RPM or vehicle speed. This test will light all CCD controlled lamps for verification of lamp operation. It also forces the odometer vacuum fluorescent display (VFD) to count up from zero through nine. The self test routine can be entered by pushing and holding the trip reset button while rotating the ignition key from the "OFF" to the "ON" position.

The 1999 TJ cluster provides bus bias and the engine controller provides termination. If either of these components are disconnected, the bus will not be operational. Starting in 1998, the cluster also provides termination as a backup to the engine controller.

The cluster will be serviced as an assembly. There will be limited parts available, bulbs and sockets, the front lens, the trip odometer stem cover and the rear cover assembly. No internal parts of the cluster will be serviced.

Engine Temp Critical - when gauge reaches the high end of the red zone.
Oil Pressure Low - below 6 psi and above 300 RPM.
Volt Gauge Low - when engine controller sets the "charge fail" DTC.
Volt Gauge High - when engine controller sets the "voltage high" DTC.

Normal Operation: At key ON, the cluster will light the low fuel, seat belt, check gauges, airbag and/or smart key immobilizer and upshift lamps (if equipped). As the key is turned farther towards the start position, the ABS (if equipped) and brake warning lamp will illuminate. The vacuum fluorescent (VF) display will indicate the last selected mode, odometer or trip. If there is a bus failure and the cluster cannot receive distance pulses from the PCM, the cluster will display the last mileage stored until the ignition is turned OFF. If the cluster is receiving bus messages but is unable to display odometer information because of an internal failure, the odometer will display dashes. VF dimming is handled by the potentiometer that controls instrumentation illumination. The odometer will remain in the last mode selected, trip or vehicle mileage after each key cycle.

Rear Window Defogger
The timing circuit for the rear window defogger is contained in the cluster. The operation is as follows:
With ignition ON, the first push of the defogger button will start a 10 minute timer. After 10 minutes have elapsed, the defogger will be turned OFF. If the button is pushed a second time during the same ignition cycle, the timer will turn the defogger on for 5 minutes. Every consecutive push will operate the defogger for 5 minutes. When the defogger is ON, it can be turned OFF with a second push of the defogger button.

Chime
The chime function is a 1000 Hz tone contained with in the cluster. The cluster will not generate more than one chime per condition in the same ignition cycle. If a problem occurs that requires a second chime while the first one is currently being generated, the second chime request will be ignored. The chime will sound for the following conditions:

Seat Belt Warning - 6 seconds after key on
Key In Ignition Warning - door open with key in ignition
Engine Temp High - when gauge enters red zone

Lamps (Hardwired)
The following lamps are hardwired in the cluster and are not part of the self-test.

Full Time 4WD (export only)
Part Time 4WD Full Time 4WD (export only)
Part Time 4WD
Brake WARNING (red)
ABS (amber)
High Beam
Left Turn Signal
Right Turn Signal
Master Illumination (export only)

Lamps (CCD)
The following lamps are controlled by the cluster via CCD messages. They are actuated during the self-test procedure.

Low Fuel Warning Airbag
Seat Belt
Upshift (if equipped)
Check Engine
Check Gauges
Smart Key Immobilizer (if equipped)

DIAGNOSTICS
Gauges
The instrument cluster will not store any DTCs. Because the engine controller gathers all the gauge information and sends it to the cluster via the bus, it is the PCM's responsibility to monitor these inputs and store DTC's for them, For this reason the first item to be checked regarding a gauge problem (except oil pressure) should be the PCM for any DTCs relating to the gauge in question.

There are DTCs associated with all the gauges except for the oil pressure gauge. When diagnosing gauges, the input that is used for the gauge message (fuel level sender for example) must be valid. Because of OBD II requirements, most of the information used for monitoring the OBD II system happens to be the same information used by the PCM to formulate the gauge bus messages. OBD II requirements state that the fuel level sender must be checked for rationality. This includes determining if the sending unit voltage is too high or too low or if the voltage hasn't changed over time. If the PCM has determined that the sender information isn't valid, it will set a diagnostic trouble code. The presence or absence of the fuel level sending code in the PCM is an important factor to determine whether a fuel gauge problem is in the sending unit or the cluster.

This same situation is used in all cluster diagnostics related to gauge operation with the exception of the oil pressure gauge. OBD II requirements do not include oil pressure monitoring. Therefore, oil pressure diagnostics would dictate that a mechanical oil pressure gauge be attached to the engine for absolute verification of oil pressure readings.

Hardwired Lamps
The cluster contains several hardwired lamps described earlier. These lamps are set up in two configurations. Either the lamp is supplied power by the cluster and the ground is supplied by the circuit being monitored or the lamp is supplied by the ground in the cluster and power comes from a module or other device. Refer to the schematic for the specific details on the lamp in question. Verification of the bulb filament may be required in all cases of an inoperative lamp. This will require removal of the cluster and the bulb in question.

CCD Controlled Lamps
The cluster contains several CCD controlled lamps as described earlier. These lamps are part of the diagnostic self-test. When entering the self-test mode, operation of these lamps can be observed. If the bulb fails to operate during the self-test and the bulb filament is good, the cluster assembly will need to be replaced.