Part 1 of 2
IDENTIFICATION OF SYSTEMThe vehicle systems that are part of the "body" system are:
- Airbag system
- Chimes
- Compass/mini-trip
- Door ajar
- Exterior lighting
- Interior lighting
- Manual A/C
- Mechanical Instrument Cluster (MIC)
- Power door locks
- Power Top
- Remote Keyless Entry (RKE)
- Sentry key immobilizer system
- Vehicle communication
- Vehicle Theft Security System (VTSS)
- Wipers
Vehicles equipped with the premium body control module can be identified by the presence of the remote keyless entry system (RKE), vehicle theft security system (VTSS) or headlamp time delay. Vehicles with the base body control module do not have these systems. A body control module that does not have these systems but does have power door locks is called a "base" on JX.
SYSTEM DESCRIPTION AND FUNCTIONAL OPERATION
A/C switch status/evaporator temperature status
When the ignition is in the "run" position, the Body Control Module (BCM) monitors the evaporator temperature and the status of the A/C switch. Based on this information, the BCM sends a CCD message to the Powertrain Control Module (PCM) indicating the A/C switch status and the evaporator temperature status.
AIRBAG SYSTEM
The airbag system is designed to proved increased driver and passenger protection if the vehicle is involved in a front-end collision. The system is most effective when used in conjunction with the seat belt system. Currently, Daimler Chrysler Corporation uses two types of airbag control modules. The AECM is an electronically triggered system that used only its own internal electronic sensor to trigger the airbags. The JX Body used only the AECM system.
Whenever the ignition key is turned to the "run" or "start" position, the Airbag Control Module (ACM) performs a lamp check by turning the AIRBAG warning lamp ON. The lamp stays lit for six to eight seconds, then goes OFF. If the lamp remains OFF, it means that the ACM has checked the system and found it to be free of discernible malfunctions. The airbag system is monitored by the ACM.
The ACM monitors critical input and output circuits within the airbag system, making sure they are operating correctly. Some circuits are tested continuously; others are checked only under certain circumstances. The ACM provides diagnostic information about the airbag system to the technician through the DRB III(R) via the CCD bus.
The deceleration or g-force resulting from the impact of a front-end collision causes the electronic sensor inside of the ACM to be triggered. This causes the inflators to be actuated, thus deploying the airbags. The total time between determining to deploy and deflation of the airbag is 1/10th of a second.
The AIRBAG warning lamp is the only point at which "symptoms" of a system malfunction can be observed by the customer.
Use the test procedures in this book to find the cause of any customer complaint regarding the AIRBAG warning lamp, such as:
- Warning lamp does not come ON at all
- Warning lamp stays ON
BODY CONTROL MODULE
The Body Control Module (BCM) supplies vehicle occupants with visual and audible information and controls various vehicle functions. To provide and receive information, the module is interfaced to the vehicle's serial bus communications network (the Chrysler Collision Detection bus, or CCD bus). This network consists of the Powertrain Control Module (PCM), the Transmission Control Module (TCM), the Electro/Mechanical Instrument Cluster (MIC), the Compass/Mini-Trip Module, the Airbag Control Module (ACM), the Sentry Key Immobilized System (SKIM) and the Antilock Brake Module (CAB). The BCM is operational when battery power is supplied to the module. Ignition switch power is needed for ignition switch functions.
The body control module provides the following features:
- A/C switch status/evaporator temperature status
- Automatic door locks Chimes
- Courtesy lamps
- BCM diagnostic support
- Door lock inhibit
- Headlamp time delay
- Illuminated entry
- Instrument panel dimming
- Manual A/C (mode door control)
- Mechanical instrument cluster support
- Power door locks (with/without remote keyless entry)
- Vehicle theft security system (VTSS)
- Windshield wiper/washer
- Power top inhibit
COMPASS/MINI-TRIP COMPUTER
The Compass/Mini-Trip Computer (CMTC) system is located on the right hand side of the instrument cluster. The CMTC is an electronic control module with a Vacuum Fluorescent Display (VFD) and two function switches. The CMTC is capable of displaying compass, temperature and trip computer information. Actuation of the STEP switch will cause the CMTC to change mode of operation while actuation of the US/M switch will toggle between English and Metric units. A reset of the trip computer is accomplished by pressing the STEP and US/M switches simultaneously.
The CMTC is active only when the ignition is ON. Upon ignition the CMTC will turn ON all of the segments in the display for one second, then revert to the last function screen that was displayed prior to the last ignition cycle. The functions that are available via actuation of the STEP switch are as follows:
- Compass and ambient temperature
- Average trip fuel economy (AVE ECO)
- Estimated Range (RANGE)
- Present fuel economy (ECO)
- Trip odometer (ODO)
- Elapsed ignition ON time (ET)
- Blank screen (OFF)
MANUAL A/C (HVAC)
The Body Control Module controls the mode door position by receiving different voltage levels from the HVAC control over the HVAC mode sense circuit. Included in this signal is the input for the rear window defogger. In this system, the body control module has no control of the blower motor or the passenger compartment temperature.
Mode Door Operation
The DRB trouble codes that indicate a stall failure or a feedback signal failure work together to show what is wrong with the HVAC system.
The stall trouble codes mean that the Body Control Module cannot force an actuator to the end of the Mode Door travel. Internal problems in the body control module will set other short-related trouble codes. Having only stall trouble codes indicates that there is a problem with an open or short circuit in the wiring, a bad actuator, a bad Mode Door or connecting linkage. It is important that the operation of the Mode Door be checked if an actuator is removed. This can be checked by rotating the door shaft to confirm that the door will stop at both ends of travel. The actuator itself has no stops. It must have the Mode Door stop travel to pass the stall test.
A feedback signal failure can occur on the Mode Door. The Body Control Module monitors the feedback signal to check the position of the actuator. The Body Control Module not only checks the level of the signal but also how much voltage changes.
A feedback failure can occur if there is a short or open circuit in the wiring, a bad Body Control Module, a bad Mode Door or connector linkage. The easiest way to diagnose this is to use the DRB to actuate the mode door. Note the feedback voltage of the actuator should smoothly change as the actuator is moved. A sudden change in the feedback voltage to a 5.0-volt or a 0.0-volt level indicates the actuator is bad. A fixed feedback voltage that is less than 5.0-volts or greater than 0.0 volts without a stall failure, or a short failure indicates that the actuator, the Mode Door, or a connecting mechanical linkage is jammed preventing movement. A feedback signal voltage that stays on 5.0 volts or 0.0 volts indicates a wiring or Body Control Module problem.
The feedback failure trouble code can also occur from a lack of actuator travel. This can be checked by confirming that the feedback signal smoothly changes when the actuator is moved with the DRB III(R). If the signal is ok and the door travel is not correct, the actuator must be removed and the mode door mechanically checked for proper operation. Typical problems that prevent door movement include screws dropped in the A/C unit or warped doors. Replace any part that is found defective.
Anytime the voltage to the BCM is interrupted for less than 2 minutes or voltage drops below approximately 10.0 volts (battery disconnected, etc.), it may be necessary to recalibrate the mode door. This can be done by using the DRB, or removing the IOD (MI) fuse for 10 seconds, reinstall it and then start the engine.
MECHANICAL INSTRUMENT CLUSTER
The Body Control Module sends the angular position of four gauges, the status of seven indicator lamps and the status and dimming of the PRNDL indicator (VF display). It also sends information of the dimming of cruise and low fuel lamps to the mechanical instrument cluster (MIC) over the CCD bus when the ignition is in the "OFF" (unlock), "run" or "start" positions. The PRNDL indicator works when the ignition is in the "OFF" , "run" or "start" positions; all other MIC features work only when the ignition is in the "run" position. On transition of the ignition from the "OFF" to the "run" position, a bulb check is performed. This consists of activating all CCD-controlled indicator lamps and all PRNDL segments for approximately two to four seconds. The PRNDL bulb check is aborted if the gear selector is moved from the PARK position, or if the tachometer exceeds 450 rpm. The ABS warning lamp is hard wired to the cluster. However, if communication is lost to the ABS module, the MIC will turn ON the warning lamp.
A new diagnostic feature has been added to the cluster software. If the cluster loses bus communication specifically with the Powertrain Control Module for more than 20 seconds, the MIL lamp will turn ON and the "No Bus" message will be shown in the VF display. If communications are reestablished, then both the MIL lamp and VF display are cleared. It is important to note that no DTC's will be set.
POWER DOOR LOCK SYSTEM
When the BCM receives an input for a lock/ unlock request (door lock switch, RKE or door key cylinder switch (w/VTSS only), it will ground the appropriate relay for a specified amount of time. For this vehicle all door lock relays are located inside the Body Control Module and are not serviced separately. The door lock switches provide a variable voltage (multiplexed (MUX) circuit) to the BCM and the BCM will respond to that command. If the conditions for door lock inhibit exist (key in ignition and left front door open), the BCM will not respond to a lock command.
Other power door lock features:
Automatic Door Locks - This feature can be enable/disabled by using either the DRB III(R) or customer key cycle method. When enabled, all the doors will lock when the vehicle reaches a speed greater than 15 MPH, all doors are closed and an increase of TPS signal is received by the PCM. If a door is opened and the vehicle slows to below 15 MPH, the door locks will operate again once all doors are closed and the vehicle speed accelerates above 15 MPH.
RKE (Remote Keyless Entry) - The body control module receives and decodes messages from the remote keyless entry transmitter. The remote keyless entry module is built into the BCM (premium) and is not serviced separately The antenna for the RKE is located in the I/P harness and connects directly to the Body Control Module. When the lock button is pressed all doors will lock, horn will chirp (if programmed), courtesy lamps will turn OFF and VTSS (if equipped) will arm. If the lock button is pressed a second time, the headlamps will flash once as a visual response. When the unlock button is pressed once, the left front door will unlock, courtesy lamps will light (if equipped w/illuminated entry) and VTSS (if equipped) will disarm. If the unlock button is pressed a second time (within five seconds of the first), the passenger door will unlock. Panic mode is accomplished by pressing the panic button for one second. This flashes the lights and sounds the horn, but does not prevent the engine from running.
The BCM will ignore all commands from the transmitter if the vehicle speed is over 15 MPH. This allows the engine to be running during warm up on cold days and allows the RKE to be used to unlock the doors.
The RKE software can store up to four transmitter codes. Use the DRB III(R) to program transmitters.
Rolling Code - The rolling code feature changes part of the key fob (transmitter) message each time it is used. The key fob message and the receiver message increment together. Under certain conditions with a rolling code system (like pressing a button on the fob over 250 times outside of the receiver range) the receiver and transmitter can fall out of synchronization. To re-synchronize, press and hold the lock and decklid release buttons simultaneously for 5 seconds. Release the buttons and wait until the doors unlock. This may take as long as 6 minutes.
POWER TOP INHIBIT (PTI)
The power top inhibit feature on JX vehicles will prevent the operation of the power top if the vehicle speed is above 10 MPH. This is accomplished by the power top inhibit relay being controlled by the body control module. The feed circuit to the power top switch is controlled by the power top inhibit relay.
SENTRY KEY IMMOBILIZER SYSTEM (SKIS)
The SKIS is an immobilizer system designed to prevent unauthorized vehicle operation. The system consists of a Sentry Key Immobilizer Module (SKIM) and ignition key(s) called Sentry Key(s) which are equipped with a transponder chip. The SKIM communicates over the Chrysler Collision Detection (CCD) data bus network to the Powertrain Control Module (PCM), Body Control Module and/or the DRBIII(R) scan tool.
When the ignition is turned to the Run/Start position, the SKIM produces a Radio Frequency (RF) via an antenna which is located around the ignition lock cylinder. The RF powers up the transponder chip inside the Sentry Key. The transponder chip then emits a coded signal that is received by the SKIM antenna. If this coded signal is valid, the SKIM sends a "Valid Key" message to the PCM. If the first transponder signal is not valid, the SKIM will attempt four more times to receive a correct transponder signal. If a valid signal is not received, the SKIM stores a diagnostic trouble code and sends an "Invalid Key" message to the PCM. Then the PCM will only allow the engine to start for two seconds then stall.
This start and stall will be allowed up to six times, after which the PCM will disable the starter relay.
The SKIS includes three valid Sentry Keys from the factory. If the customer wishes, additional uncoded Sentry Key blanks are available. These blank keys must be cut to match a valid key, but the engine will not start unless the transponder chip inside the blank key is programmed to that particular vehicle.
The Sentry Key Immobilizer System (SKIS) can be programmed to recognize a total of eight keys.
The SKIM also sends messages to the body control module over the CCD bus to control the VTSS indicator lamp. The SKIM sends a message to the body control module to turn the lamp ON for about three seconds when the ignition is turned to the Run/Start position as a bulb test. If the indicator lamp comes ON and stays ON after the bulb test, it indicates that the SKIM has detected a system malfunction and/or that the SKIS has become inoperative. If an invalid key is detected in the ignition key cylinder with the ignition switch in the Run/ Start position, or when the SKIM has entered its customer key programming mode, the SKIM will flash the VTSS indicator lamp ON and OFF.
Sentry Key Immobilizer Trouble Codes
Typically, modules have Diagnostic Trouble Codes that are referred to as either active or stored. In the case of the Sentry Key Immobilizer Module, however, all codes are stored codes. The two various types of stored codes in the SKIM can be considered to be either current or pre-existing codes. If more than one code exists, diagnostic priority should be given to the current code(s). A current code indicates a malfunction that is active at the time of vehicle service. A pre-existing code indicates the malfunction is not currently present. If a malfunction is not detected after 80 ignition cycles, it will automatically be erased.