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 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." This network consists of the Instrument Cluster (IC) that supplies both bias and termination and the PCM that provides a second termination. Bias is the part of the voltage divider network that places both bus+ and bus- at 2.5 volts. Termination in the circuitry is required to complete the voltage divider network and it also provides some electromagnetic protection for the bus.
NOTE: Communication over the bus is essential to the proper operation of some vehicle systems, On Board Diagnostic (OBD) systems and communication with the DRB. Problems with the operation of the bus or DRB must be corrected before proceeding with diagnostic testing.
- CCD Bus Failure Messages
- Short to Battery - Either or both of the bus wires are shorted to the battery potential.
- 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 or a specific ground may be open.
- Bus (+) and Bus (-) Shorted Together - The two bus wires are shorted together.
- 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 Termination - The bus system has lost connection with all of its terminators. The Instrument Cluster (MIC) and Power Train Controller (PCM) supplies termination for the 1997 Jeep Cherokee.
- 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 1997 Jeep Cherokee.
- Not Receiving Bus Messages Correctly - The DRB cannot communicate over the bus and does not know why
Using the DRB
Refer to the DRB user's guide for instructions and assistance with reading trouble codes, erasing trouble codes, and other DRB functions.
DRBIII Error Messages and Blank Screen
Under normal operation, the DRB will display one of only two error messages:
-User-Requested WARM Boot or User-Requested COLD Boot
If the DRB should display any other error message, record the entire display and call the MDS Hotline, or call for information and assistance at 1-800-825-8737. This is a sample of such an error message display:
ver: 2.14
date: 26 Jul93
file: key~iff.cc
date: Jul 26 1993
line: 548
err: Ox1
User-Requested COLD Boot
Press MORE to switch between this display and the application screen.
Press F4 when done noting information.
DRBIII Does Not Power Up
If the LED's do not light or no sound is emitted at start up, check for loose cable connections or a bad cable. Check the vehicle battery voltage (data link 16-way connector cavity 16). Am minimum of 11 volts is required to adequately power the DRB.
If all connections are proper between the DRB and the vehicle or other devices, and the vehicle battery is fully charged, an inoperative DRB may be the result of faulty cable or vehicle wiring. Perform Vehicle Communication TEST 1A.
Display is Not Visible
Low temperatures will affect the visibility of the display. Adjust the contrast to compensate for this condition.