Part 3 of 3

COMPASS MINI-TRIP COMPUTER (CMTC)
This system, located in the overhead console, displays information on outside temperature, compass direction and trip information.

Compass/Temperature Display
This display provides one of eight compass readings to indicate the direction the vehicle is facing and the outside temperature. Pressing the US/M button for more than 10 seconds will toggle to the Compass/Compass in Degree Display. This display provides one of eight compass readings to indicate the direction that the vehicle is facing and provides the compass direction in degrees (0 to 359 °). North is 0 °, East is 90 °, South is 180 ° and West is 270 °.

Trip Odometer (ODO)
Shows the distance traveled in miles or km since the last reset.

Average Fuel Economy (AVE ECO)
Shows the average fuel economy in MPG (miles per gallon) or L/100km since the last reset.

Instantaneous Fuel Economy
Shows the instantaneous fuel economy in MPG (miles per gallon) or L/100km.

Distance to Empty (DTE)
Shows the estimated distance that can be traveled with the fuel remaining in the tank. This is calculated using the MPG multiplied by the Fuel Tank Level.

Elapsed Time (ET)
Shows the accumulated ignition ON time whenever the CMTC is powered up until a reset takes place.

Step Button
Press this button to cycle through all the mini- trip computer displays.

US/M Button
Press this button to convert all vehicle displays from US to Metric and vice versa.

To Reset the Display
Press the Step and US/M buttons simultaneously for at least two seconds and all resettable conditions will be reset. This will occur only if a resettable function (AVG ECO, ECO, ET) is currently being displayed.

Compass Calibration
This is a Fast Auto-Cal compass that manually enters the calibration mode when the US/M and Step buttons are pressed for more than 6 seconds in the Compass/Temperature screen. The "CAL" will illuminate to indicate the compass is in calibration mode. Drive the vehicle around in all four compass directions, such as driving around a street block several times or driving in 2-3 circles with a slow to medium speed. When the calibration process is completed, the "CAL" will go OFF and the compass will function normally. The calibration should take place in an area that is leveled and minimum of 50 feet away from metal objects, power lines, buildings and large steel structures.

If the "CAL" message remains in the display, either there is excessive magnetism near the compass, or the unit is faulty. If the wrong direction is still indicated in the compass display, the area selected for calibration may be too close to a strong magnetic field. If the compass cannot be calibrated, further diagnosis is necessary.

Compass Variance
Compass Variance is the difference between Magnetic North and Geographic North. In some areas of the country, the difference between Magnetic and Geographic North is great enough to cause the compass to give false readings. If this occurs, the compass variance must be set.

To Set the Variance
Turn the ignition ON and set display to Comp./Temp. Simultaneously press both the US/M and STEP button for 0.1 to 2 seconds. The VAR. indicator will light up and the current zone number will be displayed. Press STEP button to select the proper variance zone as shown on the map. After 5 seconds of inactivity the displayed zone will be automatically set, and normal operation will resume.

MECHANICAL INSTRUMENT CLUSTER (MIC)
The highline MIC is only available for gas vehicles. The gauges are positioned with information received by the cluster over the CCD bus from the PCM. The MIC is hardwired to the CTM providing 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 indicators for verification of indicator operation. It also forces the odometer Vacuum Fluorescent Display (VFD) 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 word "check" appears release the knob and the test will continue.

The Powertrain Control Module diagnostic trouble codes (P-Codes) are displayed in the cluster odometer. A diagnostic trouble code display request will be initiated by the JTEC after 3 successive ignition cycles from "OFF" to "RUN" position. The cluster will display the received four digit P-Code for 4 seconds, then display 6 dashes and another P-Code. At the end when all the P-Codes are done the cluster will display "DONE" on the odometer.

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 service 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.

Normal Operations
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 (VFD) 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. Also, if there is a CCD bus failure, "no bus" will be displayed on the odometer 20 seconds after the vehicle is started.

Indicators (Hardwired)
The following indicators are hardwired in the
cluster and are not part of the self-test.
Full Time 4WD
Seat Belt
Brake Warning
High Beam
Left Turn Signal
Right Turn Signal
Low Wash Fluid Level
Wait to Start

Indicators (CCD)
The cluster via CCD messages controls the following indicators. They are actuated during the
self-test procedure.
ABS (amber)
Low Fuel Warning - Internally Controlled by the
Cluster not CCD
Airbag
Upshift (if equipped)
Check Engine
Check Gauges
Cruise Control Lamp
Trans Temp
O/D OFF (if equipped)
Water in Fuel
Maintenance Required (5.9 Heavy Duty only)

NOTE: THE SEAT BELT AND LOW WASHER FLUID SWITCH ARE HARDWIRED TO THE CLUSTER. THE CLUSTER THEN DECIDES IF THE INDICATOR 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 time 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 message. 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 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 Indicators
The cluster contains several hard wired indicators described earlier. These indicators are set up in two configurations. Either the cluster supplies power and ground is supplied by the circuit being monitored or the indicator 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 indicator 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 INDICATORS EXCEPT THE WAIT TO START INDICATOR ARE LIGHT EMITTING DIODES (LED). LED'S ARE NOT REPLACEABLE, IF DEFECTIVE THE INSTRUMENT CLUSTER MUST BE REPLACED.

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

NOTE: THE SEAT BELT INDICATOR FLASHES WHEN THE AIRBAG WARNING INDICATOR IS NOT OPERATING PROPERLY.

VEHICLE COMMUNICATION
The Chrysler Collision Detection multiplex system (CCD bus) consists of a twisted pair of wires. These wires run from one module to another. They receive and deliver coded information between the modules. The information is coded to identify the message as well as the importance of the message. When there are multiple messages trying to access the CCD bus at one time, the code determines the message that has the higher priority, and is then allowed to access the bus first.

The two wires of the twisted pair that make up the CCD multiplex system are called "bus +" (bus plus) and "bus -" (bus minus) respectively. Each wire has a measurable voltage level of roughly 2.5 Volts. In order to maintain the 2.5 Volts on each line and provide a means of transportation for the coded messages, there is a voltage divider network located in the module that supplies bus bias or voltage. Along with the module that supplies bias, some modules provide termination. Bias is the voltage necessary to make the bus operational. At least one point of termination is necessary, some systems use more than one. Some modules are capable of biasing and terminating the bus by themselves. Termination in the circuitry (a 120 ohm resistor placed across the bus) is required to complete the voltage divider network circuit and also provide some electromagnetic protection for the bus. Without termination, voltage on the bus goes to approximately 5 Volts on one wire and 0 Volts on the other wire. In the 2001 Ram Truck, the instrument cluster supplies bus bias and termination and the PCM supplies and additional point of termination.

NOTE: COMMUNICATION OVER THE BUS IS ESSENTIAL TO THE PROPER OPERATION OF THE VEHICLES ON-BOARD DIAGNOSTIC SYSTEMS AND THE DRB III. PROBLEMS WITH THE OPERATION OF THE BUS OR THE DRB III MUST BE CORRECTED BEFORE PROCEEDING WITH DIAGNOSTIC TESTING. IF THERE IS A PROBLEM, REFER TO THE VEHICLE COMMUNICATIONS.

Bus Failure Messages
Short to Battery - Either or both of the bus wires are shorted to a battery potential, or a specific ground circuit may be open.

Short to 5 Volts - Either or both of the bus wires are shorted to a 5-Volt potential.

Short to Ground - Either or both of the bus wires are shorted to ground.

Bus (+) & Bus (-) Shorted Together - The two bus wires are shorted together.

No Termination - The bus system has lost connection with all of its terminators. The Instrument Cluster (MIC) and the Powertrain Control Module (PCM) supply termination for the 2001 Ram Trucks.

Bus Bias Level Too Low - Either or both of the bus wire potentials are significantly below their normal 2.5 Volts.

Bus Bias Level Too High - Either or both of the bus wire potentials are significantly above their normal 2.5 Volts.

No Bus Bias - The bus system has lost connection with all modules that provide bias. The Instrument Cluster (MIC) provides the CCD bus bias for the 2001 Ram Trucks.

Bus (+) Open - The bus (+) wire has lost connection with termination and/or bias.

Bus (-) Open - The bus (-) wire has lost connection with termination and/or bias.

Not Receiving Bus Messages Correctly - The DRB cannot communicate over the bus and does not know why.