Mechanical Instrument Cluster

MECHANICAL INSTRUMENT CLUSTER (MIC)
The Ram Van uses a standard MIC in all of it's US vehicles. The cluster has 5 gauges and 15 indicator lamps. The gauges are positioned with information received over the CCD bus. Some of the indicator lamps are hardwired and the cluster using CCD bus information controls some. The MIC is hardwired to the CTM to provide the warning lamp announcement chimes.

There is a self test available for the cluster that will actuate all the gauges to their calibration points. The self test will not run if the cluster sees engine RPM or vehicle speed. The test will light all CCD controlled lamps for verification of lamp operation. It also forces the odometer liquid crystal display (LCD) to perform a segment check. The self test routine can be entered by pressing and holding the trip reset button while rotating the ignition key from the OFF position to the ON position. When the work "check" appears release the button and the test will continue.

The cluster will provide bus bias termination and the engine controller provides a second termination. If the cluster is disconnected, the bus will not be biased.

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

Normal Operation
At key ON, the cluster will light the low fuel, seat belt, check gauges, and airbag. As the key is turned farther towards the start position, the check engine, ABS (if equipped) and brake warning lamp will illuminate. The liquid crystal display (LCD) will indicate the mileage stored inside the cluster. If there is a bus failure and the cluster cannot receive distance pulses from the engine controller, 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 display will be blank. Dimming is handled by the potentiometer that controls instrumentation illumination.

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

- High Beam
- Left Turn Signal
- Right Turn Signal
- Brake (comes ON during self-test)
- Low Wash (comes during self-test)
- Seat Belt (comes ON during self-test)

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

- ABS lamps
- Airbag
- Check Engine
- Check Gauges
- Cruise Control Lamp
- Security
- Trans Temp
- O/D OFF
- Low Fuel Warning - Internally controlled by the cluster, not CCD

NOTE: THE TURN SIGNALS, HIGH BEAM INDICATOR, SEAT BELT WARNING LAMP, LOW WASHER WARNING LAMP AND BRAKE WARNING LAMP ARE HARDWIRED TO THE CLUSTER.

DIAGNOSTICS
Gauges
The instrument cluster will not store any DTC's. Because the engine controller PCM gathers all the gauge information and sends it to the cluster via the bus, it is the controller'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 engine controller for any DTC's relating to the gauge in question. There are DTC's associated with all the gauges except for the oil pressure gauge. When diagnosing gauges, the input that is used for 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 controller to formulate the gauge bus messages. OBD II requirement 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 send 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. The 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 diagnostic would dictate that a mechanical oil pressure gauge be attached to the engine for absolute verification of oil pressure readings.

Hard Wired Lamps
The cluster contains several hard wired lamps described earlier. The lamps are set up in two configurations. Either the cluster supplies power and ground is supplied by the circuit being monitored or the lamp is supplied ground by 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 cases of an inoperative lamp. This will require removal of the cluster and bulb in question.

NOTE: THE BRAKE, TRANS TEMP, CHECK GAUGES, SEAT BELTS AND AIRBAG WARNING LAMPS ARE LED'S, ALL OTHER ARE BULBS. IF ANY LED'S ARE DEFECTIVE,THE INSTRUMENT CLUSTER MUST BE REPLACED.

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.

NOTE: A FLASHING SEAT BELT LAMP INDICATES THAT THE AIRBAG WARNING LAMP IS NOT OPERATING PROPERLY.