1996 Town and Country- 3.3 litre- I have no voltage on my CCD Data Bus. There is supposed to be approximately 2.5 volts to ground from each of the Bus (+) and Bus (-) terminals. Does anyone know which module the bus bias is in and the bus termination is in. Thanks.

 

That 2.5v is a combination of comm pulses from affected modules, so..technically speaking there is no origin, or termination.

These are my favorite....so what is wrong that leads you to check bus wires in the first place......??

 

Thanks for the reply. Are you sure about there being no source of the biasing? I ask this because the attached file "Chrysler CCD Data Bus-2d.pdf" details the source of the "Bus Bias And Termination". I believe that this is an excerpt from a Chrysler service manual (but that could be incorrect). There was a nice wiring diagram with it but I couldn't post it because of its size. My previous question was because it didn't identify the module it was in.

In answer to your question about what the problem was that caused me to check the CCD Bus, I have attached a file "Posted.20110130.pdf" which details the problems that I am having.

In short, I believe that I have a bad BCM or PCM and am trying to determine which.

Any help would be greatly appreciated.

 

Ok.....

Technically...Yes, The BCM is your "CENTRAL" point where Biasing Occurs...But what bothers me is The 11 volts on CCD.....That is shorted to voltage without a doubt.....The other side (.5) doesnt concern you until the short to voltage is rectified....

Now...unfortunately, there is no way to know for sure whether this is a short iin wiring, or a short in a module, without Isolating the buss from ALL modules and testing for short to voltage.....

While monitoring the CCD+ at DLC.... One at a time, disconnect modules, until the voltage drops ...It may be 2.5, it may be 0...just anything other than near battery voltage. once ALL modules are Unplugged..if you still have Battery voltage on the Buss...Its time to find the "BURNT AND FUZZY" wiring harness

BUSS Education 101...... All of your Driver Information data...Gauges, overhead console info, speedo Warning lamps and even Outside temp, are available as data pulses on the buss. These pulses are interpreted by the respective module or modules, and converted into "VISUAL" objects that you see while operating the car.

What is going on here is quite simple.....The President is discretely trying to whisper NATIONAL SECURITY secrets to his Chief of staff, while they are both standing in front of the PA system at a rock concert.....

The 11 volts(LOUD MUSIC) on the buss line makes it impossibe for any of the modules to "Hear" what is being "SPOKEN" on the buss.... Once the band stops playing...everything returns to normal and the information is spoken and heard.....

Since it came and went....I would more suspect a wiring issue than a faulty module......Just for giggles....Look closely at the ABS module and harness . The way the wiring is routed , very easily lends itself to Snow, Ice and road salt damage.

 

your also gonna need a better scanner then the cheap little ones that U have been using because if U did have a bus issue then more then one module would so no commutation with each other.

 

At the start this weekend I had 0.5 volts on the + and - CCD bus. I removed the BCM from the bus and the voltage went up to 2.5 volts on both the CCD + and - bus. The resistance across the CCD + and - is 120 ohms which indicates a termination. I removed all other modules from the bus one at a time with the following results:
1) With only the ABS Brake Module connected the voltage was 2.5 which indicates that this module is the bias voltage source.
2) Only the BCM and the PCM have 120 ohm resistance which indicates termination in each of these modules.
3) All readings stay the same as I added the modules back in one at a time until all but the BCM was added back in.
4) When I added the BCM back in, the bus voltage dropped to 0.5 volts.
5) On the BCM, the resistance to ground from both CCD bus terminals is 6.8K ohms.

Does it seem correct to assume that the above indicates a problem with the BCM?

 

The Thumbs down wasnt intentional....But I cant seem to get rid of it...Ok..... Youre done.....

You went way too far, but thats ok , because you ended up at the same place.
Yes, your BCM is dragging the voltage down....... BUT...Just for gigles,,,,Unplug the ambient air temp sensor in the grille.....and see if the voltage on CCD returns.....
This is where it geys Hairy.....Not true....

As I mentioned, TECHNICALLY SPEAKING...there is no ORIGIN or TERMINATION on a buss.....

Each module is its own beginning, and its own end, and BCM is the gateway for the loop. The Bias is designed so that the voltage produced by the modules does not "STACK", but rather combines all of them into a narrow band. If you were to view a Buss on a lab scope, you would have "SPIKES" that could easily reach 6 or 8 volts. If the Bias was not Limited to the 2.5V, As soon as a module spiked at the same time as another, syatem voltage would be exceeded, and the data transmitted would be worthless. it is important to note that if ABS were offline on the buss, (LEts assume a blown fuse, and not an electronic error) the remainder of the vehicle would still function. Same with CCN (CLUSTER) or TCM. They each produce there own "DATA Voltage". Consider an Orchestra playing at the same time...Each instrument makes its own sound, but the end result is One Big Sound. Now consider a cassette tape with the orchestra recorded on it...all 96 instruments on a 1/4 inch piece of magnetic strip.... The 2.5v you see on the buss...is the condensed "TAPED" version of all those modules talking at once.