PCM CCD bus relationship - JeepForum.com
 
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post #1 of 13 Old 07-20-2021, 11:11 AM Thread Starter
variable
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PCM CCD bus relationship

I feel like this has probably been answered somewhere but I'm not searching for the right thing - sorry if that's the case..

If there is some issue with the CCD bus, or if nothing is on the bus except the PCM, will it still run? Or put another way, does the PCM need anything on the CCD bus to operate properly. More to the point, if a component on the CCD bus is causing a short, or is not terminated properly (either by a bad design or a failure), will this affect the PCM in a way that would be reflected in how the engine runs?

Still tracking down idle weirdness. I'm 90% sure that everything not wiring related (including the spark plug wires) is fine. Having encountered a number of corroded wires (which I've replaced or bypassed), it would not surprise me in the least if there was more corroded wires somewhere else I haven't thought of. AFAIK, all the engine bay grounds are good and/or new.


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post #2 of 13 Old 07-20-2021, 11:39 AM
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Problems on CCD bus can confuse the PCM enough to make the engine run poorly, yes.


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post #3 of 13 Old 07-20-2021, 12:25 PM Thread Starter
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Problems on CCD bus can confuse the PCM enough to make the engine run poorly, yes.
Hmm.. that's both helpful and unfortunate - I have something I can investigate now, however, now I have something I have to investigate... lol

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post #4 of 13 Old 07-20-2021, 01:07 PM
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depends on your year. the 93-95s dont use CCD for anything powertrain related. I believe the automatic HVAC system links to the compass with CCD, and the airbag computer does as well, i believe

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post #5 of 13 Old 07-20-2021, 01:15 PM
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be specific what is the problem, what if any codes are there?

Why would suspect bus?

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #6 of 13 Old 07-20-2021, 02:54 PM Thread Starter
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Originally Posted by jtec View Post
be specific what is the problem, what if any codes are there?

Why would suspect bus?
There's a longer thread around here somewhere with a lot more details, but the long and the short of it is that the idle will jump up for no apparent reason at a stoplight or at idle - doesn't seem to care if I'm in gear or not. As often as that happens, the idle will also fluctuate quite a bit - though not always. By quite a bit, I mean dipping to what sounds and feels like it wants to stall and then up to anywhere from 900-1200 rpm.

I've literally replaced every sensor, most of them multiple times to make sure I didn't get a garbage sensor. NTK wherever possible, the common champion plugs, etc. - all brands etc. from advice from the forum. This also includes the IAC - which is currently a mopar part, though I think I have 3 or 4 extras now from various brands. The throttlebody is about as clean as it will ever be, there's no vacuum leaks, the intake manifold gasket was replaced recently (for this issue) and I've re-done most if not all of the engine bay grounds and a couple other random unrelated grounds.

As for why I suspect the bus, I have a DRB2 that I got off ebay - which is old and used and may or may not actually work properly. Every time I hook it up, it complains the CCD bus is open on +/- (I'm going off memory here, but I know it says its open and mentions + and -). However, my Snapon tool has never complained about it.

As for codes, it starts to get weird here, which is why quite frankly, everything is suspect. The old tried and true key on/off trick stopped working. The CEL works and will come on some times as a result of it running too rich, though when it comes on, it flickers. Now, I have LED's behind the gauge cluster, and I think they're probably garbage, so the flickering may be nothing. The Snapon will catch the CEL though as well as the rich condition (I don't remember the number off hand, but I think its 52?)

The other thing I noticed after reading and reading about the IAC etc., is that when the idle is doing whatever its doing, the IAC position according the Snapon seems to get stuck - except that I know it isn't because I've tested it, by which I mean I ran it without the intake on it and watched it go from idling fine to going bonkers and I can see the IAC moving, so I know its not physically stuck, its more like its not able to tell whats going on. That or I'm getting weird info on the CCD bus and I just can't tell because the Snapon doesn't have a way to communicate that to me (thats a WAG).

VIC works, the overhead display works - compass, fuel economy, etc. etc. all miraculously work.. though I'd happily give them both up for the damn thing running right.

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post #7 of 13 Old 07-20-2021, 04:46 PM
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day is over - GTG

pick up tomorrow.
Do you have access to the DLC in diagram?

Oh as for the blinking LED's - F--- LED's. But a leaking diode in alt comes to mind.
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When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #8 of 13 Old 07-20-2021, 05:28 PM Thread Starter
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Quote:
Originally Posted by jtec View Post
Do you have access to the DLC in diagram?
Yes? Its been a while, but I don't think that connector gave me access to relevant things - isn't that one for the transmission?

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Oh as for the blinking LED's - F--- LED's. But a leaking diode in alt comes to mind.
Yeah... I'm pretty sure the gauge cluster needs to be replaced (I have another), I just haven't gotten around to it and I'll probably put 'ye ole' regular bulbs in it (and everywhere else I thought I was being clever...)

I forgot to mention that the alternator is also new - went through several iterations here as well thinking I'd gotten a bad one (or two). I also considered the voltage regulation done by the PCM might be in question so I picked up a couple external voltage regulators (suggested somewhere on here as well). Someone mentioned they don't seem to last super long which is why I picked up 2. They didn't seem to change anything noticeable or easily measured so I switched back to the built in one.

Unfortunately, a lot of the things I've replaced seem to end up in sort of a variable state - if I replace the O2 sensor because of the fuel mix and its sort of sooty, but it doesn't fix anything and the fuel mixture is still to rich, I'm still going to end up needing to replace it again at some point in the not so distant future. Same with the plugs. This is problematic as they can all be both symptom and problem; if I manage to fix the issue(s), I may not know it right away as the 02 sensor and/or plugs might be all sooty again causing the same or similar problems that I'm already having. Chicken/egg?

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post #9 of 13 Old 07-21-2021, 07:12 AM
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What I would do, my thoughts-
Use the correct bulbs!! -
Deal with rich issue later.
>> I think that will correct no CEL.
>> Allow other lights to work - ABS, security. Any known issues with them?

your buss issue
My 2₵ - one of the modules is 'off line'.
AT the connector I showed I would check for voltage on D1 and D2 ( #3 and #4) in diagram. Yes or NO?
Then checking then continuity to PCM 26 and 46.
FOllowing with a check of continuity to other modules.

more later - I will check back

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #10 of 13 Old 07-21-2021, 10:03 AM Thread Starter
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ugh... yeah.. bulbs. Technically they are correct.. they're just crap lol

One of the modules.. any guesses? Nothing seems offline. I know they relevant warning bulbs "work", they all come on like you'd expect when starting up. I generally try to avoid slamming on the brakes, and I'm not entirely sure I could apply enough pressure to lock up the wheels if ABS was offline, though I do have access to some dirt roads not too far away (if thats even a valid test). I haven't had any issues with ABS directly - some braking related annoyances, but I'm fairly certain they've nothing to do with ABS.

Security.. eh, I may need to dig through my notes and/or forum posts. I was having a problem about 9 months or so ago with something I'd wired up for remote locks as the OEM infrared remote was long gone, but I resolved it - I'm pretty sure I ultimately disabled the security system, but I'll have to check (been a while since I even thought about it).

Continuity to 26 and 46 - I assume you mean to the various modules or were you being more specific?

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post #11 of 13 Old 07-21-2021, 11:02 AM
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this is deep kimchi.
The bus is the way modules communicate, share information. Your seeing the bus is open, BUT does not check/state if an individual module is missing. SO it seams with ALL modules being on bus checking bus to each one may be necessary.

There is the PCM, Security, OVERHEAD, ABS, HVAC*, module - I think that is ALL I better check.
Any of those ring a bell as to an issue?

Referance to 26 and 46 that is the PCM terminal where BUS connects to PCM. see attachment.
There will be terminals for EACH module where bus connects, all connected. Or should be.

FYI: complicated thought here - I do NOT see the bus (d1 and D2) on the underhood connector. The PCM is reporting to your DRB a bus issue. the PCM monitors the bus
(terminals 26 and 46) and sees a problem . We are looking at the bus usiing the underdash connector.


* might be ATC system only.
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When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #12 of 13 Old 07-21-2021, 11:06 AM
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Bourbon helps. anything form buffalo trace should work.

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #13 of 13 Old 07-22-2021, 11:45 AM
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Did you resolve the issue with bus communication?

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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