Mechanical Instrument Cluster (MIC)

Mechanical Instrument Cluster (MIC)
The Ram Truck MIC is available in 2 different versions, low line and high line. The low line cluster has 2 gauges, the highline 4 gauges with twelve warning lamps. The gauges are positioned with information received by the cluster over the CCD bus from the PCM. Some of the warning lamps are hardwired and the cluster using the 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 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 liquid crystal display (LCD) to perform a segment check. 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. When the work "check" appears release the knob and the test will continue.

The cluster will provide bus bias and 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 pans 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.

Normal Operation
At key on, the cluster will light the low fuel, seat beat, 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:

- Full Time 4WD
- Seat Belt
- ABS (amber)
- High Beam
- Left Turn Signal
- Right Turn Signal
- Security (if equipped)
- Low Wash
- Wait to Start
- O/D Off (if equipped)

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

- ABS lamp
- Brake Warning
- Low Fuel Warning - Internally Controlled by the Cluster not CCD
- Airbag
- Uptight (if equipped)
- Check Engine
- Check Gauges
- Cruise Control Lamp
- Security
- Trans Temp
- O/D Off (if equipped)
- Water in Fuel
- Maintenance Required

NOTE: The seat belt and low washer switch and brake warning lamp are hardwired to the cluster. The cluster then decides if the lamp should be illuminated.
Diagnostics

Gauges
The instrument cluster will not store any DTCs. 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 DTCs 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 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 controller to formulate the gauge bus messages. OBD II Requirements State that he 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 diagnostics 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. These 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 the bulb in question.

NOTE: All red warning lamps except the wait to start lamp are light emitting diodes (LED). LED's are not replaceable, if 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.