RAM 3500 Truck 2WD V10-8.0L VIN W HDC (2000)
Central Timer Module: Description and Operation
Part 1 of 2
For additional information on the Base CTM refer to Instrument Panel, Gauges and Warning Indicators / Audible Warning Device. See: Instrument
Panel, Gauges and Warning Indicators/Audible Warning Device
SIX-STEP TROUBLESHOOTING PROCEDURE
Diagnosis of the body system is done in six basic steps:
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Verification of complaint
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Verification of any related symptoms
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Symptom analysis
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Problem isolation
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Repair of isolated problem
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Verification of proper operation
SYSTEM DESCRIPTION AND FUNCTIONAL OPERATION
The body system on the 2000 Ram Truck consists of several modules that communicate over the CCD bus (Chrysler Collision Detection multiplex
system). There are three additional modules, two types of Powertrain Control Modules (PCM) and the Controller Anti-Lock Brake (CAB) that are
not part of the body system, but do utilize the CCD bus for communication. The CAB 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, which is described in
(CCD Bus) of this general information.
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 even though a module may not require all the information to perform it's function. It
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.
AIRBAG SYSTEM
The Airbag Control Module (ACM) is secured to a bracket on the floor panel transmission tunnel below the instrument panel inside the vehicle.
The ACM mounting bracket also serves as the instrument panel center support. The ACM contains a microprocessor, the impact sensor, and
energy storage capacitor. The microprocessor contains the airbag system logic. The ACM system logic includes On-Board Diagnostics (OBD)
capability, and communicates with the instrument cluster circuitry on the Chrysler Collision Detection (CCD) data bus to control the airbag
indicator lamp.
The microprocessor in the ACM monitors the impact sensor signal and the airbag system electrical circuits to determine the system readiness. If
the ACM detects a monitored system fault, it sends messages to the instrument cluster on the CCD data bus to turn on the airbag indicator lamp. A
pre-programmed decision algorithm in the ACM microprocessor determines when the deceleration rate signaled by the impact sensor indicates an
impact that is severe enough to require airbag system protection. When the programmed conditions are met, the ACM sends and electrical signal to
deploy the airbag system components.
Only one impact sensor is used in this airbag system. The impact sensor is an accelerometer that senses the rate of the vehicle deceleration, which
provides verification of the direction and severity of an impact. The impact sensor is calibrated for the specific vehicle, and is only serviced as a
unit with the ACM.
The ACM also contains an energy-storage capacitor. This capacitor stores enough electrical energy to deploy the airbags, for one second
following a battery disconnect or failure during and 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 airbags.
WARNING: 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.
THEN 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,
AS 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 airbag warning lamp is the only point at which the customer can observe "symptoms" of a system malfunction. Whenever the ignition key is
turned to the "run" or "start" position, the MIC performs a lamp check by turning the AIRBAG warning lamp ON for 6-8 seconds. If the lamp
remains 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 internally shorted to ground. If the lamp comes ON and stays ON for a
period longer than 6-8 seconds then goes OFF, there is usually an intermittent problem in the system.
The MIC monitors the airbag warning lamp and seat belt warning lamp during the bulb check for a defective bulb or lamp driver circuit. The MIC
tests the airbag lamp during the cluster bulb check and substitutes the seat belt lamp if the airbag lamp is defective. If the airbag lamp is defective
