RAM 2500 Truck 4WD V8-5.9L VIN Z LDC (1998)
will discontinue the fault signal as soon as it sees a "normal" G-sensor input
Vehicle Communication
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 1998 Ram Truck, the instrument cluster supplies bus bias and termination and the PCM supplies an 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. Problems with the
operation of the bus or DRB must be corrected before proceeding with diagnostic testing. If there is a problem, refer to the Vehicle
Communications section of this manual.
Wiper System
Speed Sensitive Intermittent Wipers
The Ram truck equipped with a high line CTM will utilize speed sensitive intermittent wipers. Only a high line CTM will be able to support this feature.
A base CTM (IEM) will provide for intermittent wipers without the speed sensitive feature. The low and high speeds are controlled through the wiper
stalk switch. The intermittent portion of the wiper control is handled by the CTM through the intermittent wiper relay. When the module detects a
decrease in delay time as selected by the driver, an immediate wipe of the windshield takes place and the new delay interval is
implemented. This feature is present on both the base and highline CTM.
When the vehicle is moving at speeds at or below 10 mph, the delay time ranges from 1 to 36 seconds. When the speed rises above 10 mph, the delay
times are cut in half for a range of 1/2 to 18 seconds. The speed signal is provided to the CTM from the PCM over the CCD bus.
