Part 1 of 2

SYSTEM DESCRIPTION AND FUNCTIONAL OPERATION
The body system on the 2000 Jeep Cherokee consists of five modules that communicate over the CCD bus (Chrysler Collision Detection multiplex system). There are two additional modules, the Powertrain Control Module (PCM) and the Transmission Control Module (TCM) that are not part of the body system, but do utilize the CCD bus for communication. The TCM also utilizes the bus for diagnostics. The PCM sends and receives messages on the CCD bus; however, diagnostics are performed through the Serial Communication Interface or SCI, the same as last year. All of the information about the functioning of all the systems is organized, controlled and communicated by the CCD bus.

Through the CCD bus, information about the operation of vehicle components and circuits is relayed quickly to the appropriate module(s). All modules receive all the information transmitted on the bus although a module may not require all information to perform its function. Each module will only respond to messages "addressed" to it through a binary coding process. This method of data transmission significantly reduces the complexity of the wiring in the vehicle and the size of wiring harnesses.

When replacing a blown fuse, it is important to use only a fuse having the correct amperage rating. The use of a fuse with a rating other than indicated may result in a dangerous electrical system overload. If a properly rated fuse continues to blow, it indicates a problem in the circuit that must be corrected.

When replacing any bulbs, do not touch the new bulb with your fingers. Oil contamination will severely shorten bulb life. If the new bulb comes in contact with an oily surface, clean the bulb with rubbing alcohol.

AIRBAG SYSTEM
A dual front airbag system is a standard equipment safety feature on this model. The airbag system is designed to provide increased driver and passenger protection if the vehicle is involved in a front-end collision. A DRBIII (R) scan tool is required for diagnosis of the airbag system. The system is the most effective when used in conjunction with the seat belt system. The airbag system consists of the Airbag Control Module (ACM), Mechanical Instrument Cluster (MIC), driver and hybrid passenger airbag module, clock spring, data link connector and the Chrysler Collision Detection multiplex system (CCD bus). There are no external impact sensors in this system.

The ACM is an electronic module that monitors the airbag system for proper operation, stores Diagnostic Trouble Codes (DTCs), controls the airbag warning lamp, and contains an energy storage capacitor. This capacitor stores enough electrical energy to deploy the airbags for up to one second following a battery disconnect or failure during an impact. The purpose of the capacitor is to provide airbag system protection in a severe secondary impact if the initial impact has damaged or disconnected the battery, but was not severe enough to deploy the airbag.

The ACM is mounted on the center tunnel floor pan of the vehicle, behind the parking brake mechanism. The ACM provides DTCs to the technician through the DRBIII (R) via the CCD bus. Some circuits are tested continuously; others are checked only under certain circumstances. The Mechanical Instrument Cluster (MIC) turns the warning lamp on or off based on CCD bus messages from the ACM. The ACM cannot be repaired and must be replaced if it is damaged or faulty.

THE AIRBAG SYSTEM IS A SENSITIVE, COMPLEX ELECTROMECHANICAL UNIT. BEFORE ATTEMPTING TO DIAGNOSE OR SERVICE ANY AIRBAG SYSTEM OR RELATED STEERING WHEEL, STEERING COLUMN OR INSTRUMENT PANEL COMPONENTS, YOU MUST FIRST DISCONNECT AND ISOLATE THE BATTERY NEGATIVE (GROUND) CABLE. WAIT TWO MINUTES FOR THE SYSTEM CAPACITOR TO DISCHARGE BEFORE FURTHER SYSTEM SERVICE. THIS IS THE ONLY SURE WAY TO DISABLE THE AIRBAG SYSTEM. FAILURE TO DO THIS COULD RESULT IN ACCIDENTAL AIRBAG DEPLOYMENT AND POSSIBLE PERSONAL INJURY.

NEVER STRIKE OR KICK THE AIRBAG CONTROL MODULE BECAUSE IT CAN DAMAGE THE IMPACT SENSOR OR AFFECT ITS CALIBRATION. IF AN AIRBAG CONTROL MODULE IS ACCIDENTALLY DROPPED DURING SERVICE, THE MODULE MUST BE SCRAPPED AND REPLACED WITH A NEW UNIT.

The deceleration or g-force resulting from the impact of a front-end collision causes the safing sensor inside the ACM to close. As soon as the ACM internal accelerometer and the safing sensor are closed an electrical charge is sent to the airbag module. This causes the inflator to be actuated, thus deploying the airbags. The total time from the closure of the sensors to deployment and deflation of the airbags is 1/10 of one second.

The AIRBAG warning lamp is the only point at which "symptoms" of a system malfunction can be observed by the customer. Whenever the ignition key is turned to "run" or "start" position, the MIC performs a lamp check by turning the AIRBAG warning lamp ON for six to eight seconds. If after that the lamp turns OFF, it means that the ACM has checked the system and found it to be free of discernible malfunctions. If the lamp remains ON, there could be an active fault in the system or the MIC lamp circuit may be defective. If the lamp comes ON and stays ON for a period longer than six to eight seconds and then goes OFF, there is usually an intermittent problem in the system. The MIC monitors the airbag warning lamp for an open or defective lamp driver circuit. This information is sent to the ACM via a CCD bus message. The CCD bus messages listed below can be monitored using DRBIII (R) and selecting "passive restraints," "AIRBAG," "MONITOR DISPLAY," and "WARNING LAMP STATUS."

ACM LAMP REQUEST (ON or OFF)
MIC BULB STATE (OK or failed)
MIC DRIVER STATE (OK or failed)

Perform the WARNING LAMP CIRCUIT OPEN procedure in this book to find the cause of any customer complaint regarding the AIRBAG warning lamp, such as:
- Warning lamp does not illuminate
- Warning lamp stays illuminated with no active DTCs


NOTE: THE AIRBAG WARNING LAMP WILL BE ILLUMINATED IF THE INSTRUMENT CLUSTER LOSES CCD BUS COMMUNICATION WITH THE AIRBAG MODULE OR PCM. THE CCD BUS SYSTEM MUST BE REPAIRED FIRST.

Service and general information labels about the airbag system can be found on the driver's sun visor, and in the engine compartment.

To ensure that the airbag will be ready to deploy in a collision, have the system serviced by an authorized dealer.

IMPORTANT NOTE: IF THE POWERTRAIN CONTROL MODULE HAS BEEN CHANGED AND THE CORRECT VIN AND MILEAGE HAVE NOT BEEN PROGRAMMED, A DTC WILL BE SET IN THE AIRBAG MODULE. IN ADDITION, IF THE VEHICLE IS EQUIPPED WITH A SENTRY KEY IMMOBILIZER MODULE (SKIM). SECRET KEY DATA MUST BE UPDATED TO ENABLE STARTING.

FOR AIRBAG SYSTEM:
ACTION:
1. Enter correct VIN and Mileage in PCM.
2. Erase codes in Airbag module.

Driver Airbag Module (DAB)
The Driver Airbag Module (DAB) protective trim cover is the most visible part of the driver side airbag system. The module is mounted directly to the steering wheel. The protective trim cover is fitted to the front of the airbag module and forms a decorative cover in the center of the steering wheel. Upon airbag deployment, this cover will split at a predetermined breakout line. Located under the airbag module trim cover are the born switch, the airbag cushion and the airbag cushion supporting components. The airbag module includes a housing to which the cushion and inflator are attached and sealed. The airbag module cannot be repaired and must be replaced if deployed or is damaged or defective in any way. The inflator assembly is mounted to the back of the airbag module. When supplied with the proper electrical signal, the inflator seals the hole in the airbag cushion so it can discharge the gas it produces directly into the cushion.

THE AIRBAG MODULE INFLATOR ASSEMBLY CONTAINS SODIUM AZIDE AND POTASSIUM NITRATE. THESE MATERIALS ARE POISONOUS AND EXTREMELY FLAMMABLE. CONTACT WITH ACID, WATER OR HEAVY METALS MAY PRODUCE HARMFUL OR IRRITATING GASES (SODIUM HYDROXIDE IS FORMED IN THE PRESENCE OF MOISTURE) OR COMBUSTIBLE COMPOUNDS. IN ADDITION, THE PASSENGER AIRBAG MODULE CONTAINS ARGON GAS PRESSURIZED TO OVER 2500 PSI. DO NOT ATTEMPT TO DISMANTLE AN AIRBAG MODULE OR TAMPER WITH ITS INFLATOR. DO NOT PUNCTURE, INCINERATE OR BRING INTO CONTACT WITH ELECTRICITY. DO NOT STORE AT TEMPERATURES EXCEEDING 93 °C (200 °F).

The DAB is connected to the ACM through a mechanical device called a clock spring. The clockspring allows the DAB to be hardwired through the steering wheel to the ACM. A yellow quick disconnect connector is located under the steering column at the lower edge of the knee blocker panel. This connector when disconnected will disable both the DAB and PAB modules.

THE AIRBAG SYSTEM IS A SENSITIVE, COMPLEX ELECTROMECHANICAL UNIT. BEFORE ATTEMPTING TO DIAGNOSE OR SERVICE ANY AIRBAG SYSTEM OR RELATED STEERING, STEERING COLUMN OR INSTRUMENT PANEL COMPONENTS, YOU MUST FIRST DISCONNECT AND ISOLATE THE BATTERY NEGATIVE (GROUND) CABLE. WAIT TWO MINUTES FOR THE SYSTEM CAPACITOR TO DISCHARGE BEFORE FURTHER SYSTEM SERVICE. THIS IS THE ONLY SURE WAY TO DISABLE THE AIRBAG SYSTEM. FAILURE TO DO THIS COULD RESULT IN ACCIDENTAL DEPLOYMENT AND POSSIBLE PERSONAL INJURY. WHEN A STEERING COLUMN HAS AN AIRBAG MODULE ATTACHED, NEVER PLACE THE COLUMN ON THE FLOOR OR ON ANY OTHER SURFACE WITH THE STEERING WHEEL OR AIRBAG MODULE FACE DOWN.

Passenger Airbag Module (PAB)
The airbag door on the instrument panel above the glove box is the most visible part of the passenger side airbag system. Under the airbag door are the airbag cushion and its supporting components. The airbag module includes a housing to which the cushion, inflator and canister of compressed gas are attached and sealed. The airbag module cannot be repaired and must be replaced if deployed or damaged. The inflator seals the hole in the airbag cushion so it can discharge the gas it produces directly into the cushion when supplied with the proper electrical signal. The airbag door is secured to the airbag module and the instrument panel base, and has predetermined breakout lines concealed beneath its decorative cover. Upon airbag deployment, the airbag door will split at the breakout lines and the door will pivot out of the way. The airbag door is serviced as a unit with the airbag module. If an airbag module assembly is defective and non-deployed, refer to the Chrysler Corporation current parts return list in the Warranty Policies and Procedures for the proper handling procedures.

THE AIRBAG MODULE INFLATOR ASSEMBLY CONTAINS SODIUM AZIDE AND POTASSIUM NITRATE. THESE MATERIALS ARE POISONOUS AND EXTREMELY FLAMMABLE. CONTACT WITH ACID, WATER OR HEAVY METALS MAY PRODUCE HARMFUL AND IRRITATING GASES (SODIUM HYDROXIDE IS FORMED IN THE PRESENCE OF MOISTURE) OR COMBUSTIBLE COMPOUNDS, IN ADDITION, THE PASSENGER AIRBAG MODULE CONTAINS ARGON GAS PRESSURIZED TO OVER 2500 PSI. DO NOT ATTEMPT TO DISMANTLE AN AIRBAG MODULE OR TAMPER WITH ITS INFLATOR. DO NOT PUNCTURE, INCINERATE OR BRING INTO CONTACT WITH ELECTRICITY DO NOT STORE AT TEMPERATURES EXCEEDING 93 °C (200 °F).

A yellow quick disconnect connector is located under the steering column at the lower edge of the knee blocker panel. This connector when disconnected will disable both the DAB and PAB module.

THE AIRBAG SYSTEM IS A SENSITIVE, COMPLEX ELECTROMECHANICAL UNIT. BEFORE ATTEMPTING TO DIAGNOSE OR SERVICE ANY AIRBAG SYSTEM OR RELATED STEERING WHEEL, STEERING COLUMN OR INSTRUMENT PANEL COMPONENTS, YOU MUST FIRST DISCONNECT AND ISOLATE THE BATTERY NEGATIVE (GROUND) CABLE. WAIT TWO MINUTES FOR THE SYSTEM CAPACITOR TO DISCHARGE BEFORE FURTHER SYSTEM SERVICE. THIS IS THE ONLY SURE WAY TO DISABLE THE AIRBAG SYSTEM. FAILURE TO DO THIS COULD RESULT IN ACCIDENTAL AIRBAG DEPLOYMENT AND POSSIBLE PERSONAL INJURY.

REPLACE AIRBAG SYSTEM COMPONENTS ONLY WITH PARTS SPECIFIED IN THE CHRYSLER MOPAR PARTS CATALOG. SUBSTITUTE PARTS MAY APPEAR INTERCHANGEABLE, BUT INTERNAL DIFFERENCES MAY RESULT IN INFERIOR OCCUPANT PROTECTION. THE FASTENERS, SCREWS AND BOLTS ORIGINALLY USED FOR THE AIRBAG SYSTEM COMPONENTS HAVE SPECIAL COATINGS AND ARE SPECIFICALLY DESIGNED FOR THE AIRBAG SYSTEM. THEY MUST NEVER BE REPLACED WITH ANY SUBSTITUTES. ANYTIME A NEW FASTENER IS NEEDED, REPLACE IT WITH THE CORRECT FASTENERS PROVIDED IN THE SERVICE PACKAGE OR SPECIFIED IN THE CHRYSLER MOPAR PARTS CATALOG.

Airbag Diagnostic Trouble Codes
Airbag diagnostic trouble codes consist of active and stored codes. If more than one code exists, diagnostic priority should be given to the active code(s).

Each diagnostic trouble code is diagnosed by following a specific testing procedure. The diagnostic test procedures contain step-by-step instructions for determining the cause of the trouble codes. It is not necessary to perform all of the tests in this book to diagnose an individual code.

Active diagnostic trouble codes for the airbag system are not permanent and will change the moment the reason for the code is corrected. In certain test procedures, diagnostic trouble codes are used as a diagnostic tool.

Active Codes
An active trouble code indicates an ongoing malfunction. This means that the defect is currently there every time the airbag control module checks that circuit/function. It is impossible to erase an active code; active codes automatically erase by themselves when the reason for the code has been corrected.

With the exception of the warning lamp trouble codes or malfunctions, when a malfunction is detected the AIRBAG lamp remains lit for a minimum of 12 seconds or as long as the malfunction is present.

Stored Codes
Airbag codes are automatically stored in the ACM's memory after 1 minute of occurance or when the ignition is turned OFF. The exception is the "Loss of Ignition Run Only" code which is an active code only.

A "stored" code indicates there was an active code present at some time. However, the code currently may not be present as an active code although another active code could be.

When a trouble occurs, the AIRBAG warning lamp illuminates for 12 seconds minimum (even if the problem existed for less than 12 seconds). The code is stored, along with the time in minutes it was active, and the number of times the ignition has been cycled since the problem was last detected.

The minimum time shown for any code will be one minute, even if the code was actually present for less than one minute. Thus, the time shown for a code that was present for two minutes 13 seconds, for example, would be three minutes.

If a malfunction is detected, a diagnostic trouble code is stored and will remain stored as long as the malfunction exists. When and if the malfunction ceases to exist, an ignition cycle count will be initiated for that code. If the ignition cycle count reaches 100 without a recurrence of that same malfunction, that diagnostic trouble code is erased and that ignition cycle counter is reset to zero. If the malfunction recurs before the count reaches 100, then the ignition cycle counter will be reset and the diagnostic trouble code will continue to be a stored code.

If a malfunction is not active while performing a diagnostic text procedure, the active code diagnostic test will not locate the source of the problem. In this case, the stored code can indicate an area to inspect.

If no obvious problems are found, erase stored codes. With the ignition "ON," wiggle the wire harness and connectors, then rotate the steering wheel from stop to stop. Recheck for codes periodically as you work through the system. This procedure may uncover a malfunction that is difficult to locate,

Airbag Trouble Codes
The airbag control module may report any of the following diagnostic trouble codes.

For the following active or stored codes, replace the Airbag Control Module (ACM):
- AECM Accelerometer
- Internal Diagnostic 1
- Internal Diagnostic 2
- AECM Output Driver
- AECM Stored Energy Logic
- AECM Stored Energy Driver
- AECM Stored Energy Passenger
- Internal Diagnostic 3
- Internal Diagnostic 4
- Safing Sensor Shorted

For these codes, refer to the appropriate diagnostic procedure:
- Driver Squib Circuit Open
- Driver Squib Circuit Shorted
- Loss of Ignition Run Only
- Loss of Ignition Run/Start
- No Cluster CCD Bus Message
- No CCD Communication
- Passenger Squib Circuit Open
- Passenger Squib Circuit Shorted
- Either Squib Term Shorted to Battery
- Either Squib Term Shorted to Ground
- Warning Lamp Circuit Open/Shorted

COMPASS/MINI-TRIP COMPUTER
The Compass/Mini-Trip Computer (CMTC) is in the overhead console. It displays the following information:
- Compass direction
- Current outside temperature
- Elapsed Time (ET)
- Distance To Empty (DTE)
- Average Fuel Economy (AVE ECO)
- Instantaneous Fuel Economy (ECO)
- Trip Odometer (ODO)

All of the information required by the CMTC except the ambient temperature and compass direction is transmitted over the CCD bus.

The CMTC can perform an independent self-test. This can be accomplished by using either the DRB or pressing both US/M and STEP buttons and then turning the ignition key on. All segments of the CMTC should light while the CMTC checks its internal function. If there are internal failures, the CMTC will display "FAIL." If there is a problem with the CCD communication, the CMTC will display "CCD." Refer to the "Compass/Mini-Trip" for further diagnosis.

Setting The Compass
The compass/mini-trip module is self-calibrated and requires no adjustment. The word CAL will be displayed to indicate that the compass is in the fast calibrating mode. CAL will turn off after the vehicle has gone in three complete circles without stopping, in an area free of magnetic disturbance.

If the module displays the temperature while the compass is blank, or displays a false reading, the vehicle must be demagnetized.

If the compass still goes blank after the vehicle is demagnetized, the compass/mini-trip module must be replaced.




Setting The Compass Variance
Variance is the difference between magnetic north and geographic north. To determine the variance for the area you are in, refer to the zone map. The number shown for your area is the variance number for your area.

1. Set the compass/mini-trip console to compass/ temperature mode.
2. Press and hold down both the US/METRIC button and the STEP button for 5 seconds.
3. The VAR light will come on and the last variance setting will be displayed.
4. Enter the correct variance number by pressing the US/M button.
5. Press the STEP button to set the zone number and resume normal operation.

NOTE: DO NOT ATTACH ANY MAGNETIC DEVICE SUCH AS A MAGNETIC CB ANTENNA TO THE VEHICLE. THIS CAN CAUSE THE COMPASS TO GIVE FALSE READINGS.