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Old 01-24-2012, 06:21 AM
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Nominate Replacing BCM on Grand Cherokee 2.7 CRD Ltd

Hi all,

It begins to look as though my EVIC display problems are probably down to a failing BCM. Most likely due to a component that fails when it reaches a certain temperature.

After asking my local stealership "Is there any guarantee that the diagnosis, priced at 71 ($100), would pin-point the problem?"

and commenting that if the BCM proved to be the problem

".... I would want to source a second hand one. If I were to find one, which of course would need to be exactly the same Part No. as the original, could it easily be re-programmed?"

They came up with the following (semi-literate and, in my view, 'lying') comment: -

"I could only offer a guarantee on the diagnosis if we can be a 100% after carrying out the diagnosis on your vehicle,with regards to the replacement body control module if required they are not interchangable due to they are a 1 time use only,once they are programmed to a vehicle they can not be swapped onto another vehicle."
(sic)

In other words "....if you give us the freedom to mess about fitting new expensive parts, and charge exactly what we like, we may be able to get your vehicle working properly....".

My limited knowledge of electronics suggests to me that what can be programmed can be wiped and re-programmed.

Right then, to my question: -

Has anybody had experience of fitting a second-hand/previously-used BCM to their vehicle?

I don't have a problem with the mechanics of removal and re-fitting, but would like to know: -

(a) Can a BCM be re-programmed when out of the vehicle e.g. by punching the VIN code into the programmer?

(b) If a used one is fitted without re-programming could the vehicle then be driven to a stealership for re-programming, or would damage be done to the system?

I ask these questions because there is one for sale (at a sensible price) having exactly the same Part No. as mine, but it was previously fitted to a V8 Overland.

To summarise the symptoms of my possible BCM failure: -

Fault manifests as incorrect displays on EVIC e.g.: -

" - - - AVERAGE MILES/GAL"
" - - - MILES TO EMPTY"
" - - INSTANT MILES/GAL"
"- - - - TIME ELAPSED"

Other normal displays e.g. "TRIP MILES" and "MILES TO SERVICE" are O.K.
Warnings e.g. "HOOD OPEN", "DOOR OPEN" are O.K.

Symptoms accompanying above failure: -

DOOR CONTROLS
Windows lower and raise non-function. (All others, mirrors/door lock are O.K.)

STEERING WHEEL CONTROLS
Radio channel change and volume non-function. (Cruise controls O.K.)

STEERING COLUMN CONTROLS

CENTRAL. Hazard flasher O.K.
L.H.S. All light and indicator controls O.K.
R.H.S. Front and rear wipers/washers operate but intermittent wipers non-function.

INSTRUMENT PANEL
Blue 'high beam' indicator light non-function. (All other lights and gauges O.K.)

Other non-functioning items when above state exists: -

Auto seat position including 'easy exit'.
Internal lights on entry. External light flash on lock/unlock, although locking mechanism works.
(I do not know if alarm/immobiliser system is activated in these conditions).

NOTES
1) The system can be reset to normal by disconnecting and reconnecting the battery negative terminal after which all systems function normally, but only for a short while, 10 to 20 minutes, sometimes less.
2) The EVIC self-tests O.K.
3) The AZC self test yields bus errors when the above state exists, plus errors that possibly indicate broken blend doors.

Sorry to be so long winded, but I am reluctant to spend what nwould probably be over a grand ($1500) on a vehicle that would retail at only 3 to 3.5K ($4500-$5000).

Thanks to all

Tony Norton
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Old 01-24-2012, 07:00 AM
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Re: Replacing BCM on Grand Cherokee 2.7 CRD Ltd

Quote:
Originally Posted by Tony Norton View Post

Thanks to all

Tony Norton
If your username is the name as your real name I think we can understand who's thanking us. lol

That's a pretty pricy replacement for like you said a vehicle that wouldn't resell for very much. I would say do it if you plan on running it for several more years.
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Old 01-24-2012, 07:11 AM
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Re: Replacing BCM on Grand Cherokee 2.7 CRD Ltd

Tony,

Can't help with the answers however, on You tube there is a duo call Whizkid and MrFixit. Whizkid has had similar problems and was replacing his BCM and of course uploaded the work.


Last bit of correspondance suggested he hadn't fixed the problem, but he always answers emails. He may have an answer for you.
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Old 02-03-2012, 01:53 AM
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Re: Replacing BCM on Grand Cherokee 2.7 CRD Ltd

Hi There,

This sounds just like the dreaded PCI bus issue I've been dealing with for several months.
Changing parts to fix this issue is a very expensive hit and miss process, unfortunately most mechanics including the dealer may not have the experience to troubleshoot this problem.
If you can find someone with an oscilloscope to check the PCI bus you may save yourself an expensive BCM.

There are more details in this thread:

PCI Bus Issue

-J
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Old 02-03-2012, 06:18 AM
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Re: Replacing BCM on Grand Cherokee 2.7 CRD Ltd

Hi James,

You didn't say in your post on the linked thread whether or not you were experiencing all the faults that Caprice actually listed.

If so I don't think that my problems are quite the same, as I don't lose anything that is essential to driving. Gauges, lights, indicators, dash lights and warning lights all function correctly. The only things that don't work, that are highly desirable are the window controls and the high beam indicator light. The rest of non-working items all fall into the "....it would be nice if...." category.

I absolutely agree with all the adverse comments about "stealerships". In my book they are total tossers. Our local one say that, when they order a new BCM they can't programme it themselves but have to order it pre-programmed to a specific VIN number. They also reckon that they can't guarantee to find the fault after a 75 ($100+) diagnostic scan. Why the hell do they even exist. Oh yes, I forget, it's to sell overly expensive new Jeeps to local suckers!

A forlorn hope I have, as I don't think the BCM can be faulty as it will work 100% for a short period of time after either disconnecting the battery -ve or removing and replacing the IOD fuse, is that it may be related to the fact that roundabout the time that these problems manifested themselves the heater also stopped functioning properly. (Only blowing cold air.) I intend to fix this by purchasing a "JGCParts.com" kit, after first taking the 'panel cutting' steps to check that the blend doors are actually broken; and see if that improves the situation. At least, at this coldest time of the year here in U.K., I should then be comfortable driving the vehicle.

I've read that people "....check the voltages on the PCI....". I assume that this is done at the 'Diagnostic Port' which, I guess, is the one that sits next to the junction block that carries the BCM. If that is the case could somebody point me to the information on what voltages should be on what pins, and what resistance readings should I find where? I assume that voltages would be checked with power and ignition on, and resistances with power disconnected.

Advice on this would be much appreciated.

Thanks to all.
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Old 02-03-2012, 09:07 PM
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Re: Replacing BCM on Grand Cherokee 2.7 CRD Ltd

Here is some info i found on the net, not sure if its of help:

PCI Bus Diagnostics for 1999-2004 (WJ) Jeep Grand Cherokee
The PCI Bus system is a one-wire communication system. It allows the various modules (computers) on the vehicle to communicate with each other and share information. This information sharing reduces wiring complexity.
The PCI Bus wire is either yellow with a violet tracer, or white with a violet tracer, depending on year and model. The easiest place to access this wire is at the data link connector, which is the connector that the scan tool plugs into for diagnosis. On LHD North American Jeeps, the data link connector is located under the driver side of the dash, adjacent to the fuse block. It is easily visible without removing any panels.
The PCI Bus wire is in pin #2 of the data link connector. Normally I remove the connector from it's bracket and pull it down for better access. This allows me to backprobe the connector with my voltmeter. You do not want to damage the portion of the terminals which make contact with the scan tool connector.
Here are the symptoms you are probably experiencing with a PCI Bus issue:
  1. The A/C blows normal volume but the air is not cold, because the compressor will not engage, even with the 'snowflake' or 'A/C' button pressed.
  2. The instrument cluster backlighting is ON at all times (when the key is on), even with the headlamps OFF.
  3. Power windows are inoperative.
  4. The overhead console displays 'lines' instead of information.
  5. The gauges are not reading correctly.

These symptoms may come and go. Often PCI bus problems are intermittent.
The PCI Bus system operates on a 0 to 7.5 volt square wave. If you were to connect an oscilloscope to pin 2 of the data link connector, on a system with no problems, the oscilloscope would display a nice square wave. Most people do not have a $2000 scope, so I have devised an easier method. You will need a digital voltmeter to continue.
  1. Set the meter to 'DC Volts'
  2. Connect the red lead of the meter to pin 2 of the data link connector
  3. Connect the black lead of the meter to ground. Any bare metal surface under the dash will work.
  4. Turn the key to 'ON'. Or, start the engine. Sometimes the PCI Bus problem is easier to duplicate with the engine running.
  5. Observe the volt reading on the meter.

If the volt reading is zero, or very close to zero, it is possible that the PCI bus is OPEN, or SHORTED TO GROUND. A different test will be required, which is detailed later in this article.
If the volt reading is close to 12 volts, or battery voltage, the PCI Bus is shorted to voltage, and diagnosis should be fairly easy.
If the volt reading is varying between 0.5 and 2.5 volts, the fault is not present at this time. Verify this by inspecting the operation of the windows and other symptoms.
Normally what I see on problem vehicles is a reading of 4 to 6 volts. This indicates that a module (one of the vehicle computers) is pulling the bus voltage too high, causing interference and a loss of communication between modules, which leads to the symptoms you are experiencing.
If the PCI Bus voltage reading is consistently above 2.5 volts, we need to determine which module is causing the problem. There is no quick way to do this. Each module on the bus must be unplugged until the voltage returns to the 0.5 to 2.5 and fluctuating range.
Module examples are:
  1. PCM (engine computer)...engine compartment
  2. TCM (transmission computer)...engine compartment
  3. BCM (body computer)...under dash near fuse block
  4. ABS (antilock brake computer)...engine compartment
  5. Instrument cluster
  6. Airbag computer...under center console/armrest
  7. Driver door module (the window switch assembly)...remove door panel to access
  8. Passenger door module (the window switch assembly)...remove door panel to access
  9. Radio
  10. Audio amplifier...under back seat
  11. A/C control head...in dash
  12. Overhead console computer
  13. Immobilizer module...remove steering column covers to access
I begin with the interior modules, unplugging the ones that are easiest to get to. Continue to unplug modules until the bus voltage lowers to a normal level; 0.5 to 2.5 volts and fluctuating up/down randomly. Keep in mind that unplugging some modules will cause other symptoms...try to ignore those for now and focus on the voltage reading.
Once you find a suspect module, reconnect everything else and observe the bus voltage. Reconnect the suspect module and try to duplicate the symptoms. Verify that the suspect module is actually the problem several times before you spend money on a replacement part. Be sure to cycle the ignition key every once in a while during testing. The trick here is to be able to consistently verify that the bus problem is present, then verify that it is not present when the suspect module is unplugged. Try to not let the system 'fool' you.
If the bus voltage is around 12 volts, or is the same as battery voltage, and ALL modules are unplugged, then the bus wiring is shorted to voltage. This problem may not be easy to find. You will have to trace the bus wire extensively. The good news is that this scenario is very unlikely.
If the bus voltage is always near 0 volts, a different method will work.
Disconnect the vehicle battery under the hood.
Connect your meter the same way, but switch to the 'ohms' setting, to check the resistance of the bus. A bus that is shorted to ground will have a very low resistance, possibly below 10 ohms. In a situation where the bus is shorted to ground, a module could be at fault, but more likely the bus wire has rubbed through somewhere and is touching bare metal. Keep in mind that the whole frame and body of the vehicle is ground, so that makes this scenario more likely.
If the ohm reading is 'OL' meaning infinite resistance, then the bus wire is OPEN and must be traced out for continuity. However...if every module is unplugged, and the bus wiring is OK, the meter will display 'OL' for bus resistance.
Read the following information, which is from Chrysler:

Measuring PCI voltage is the first place to go if no communication is possible with any modules. This tells what type of failure has occurred and this dictates the next step. If communication is possible with only one module, an open in the bus is likely.PCI bus vehicle are very easy to diagnose bus problems on. Since each module has a termination resistor of a standard value a measurement of bus resistance (with the battery disconnected) gives a very good idea of the condition of the bus. For example: Termination resistance 350 to 750 ohms would be a normal bus. 0 ohms would indicated a shorted bus OL would indicate an open bus 3300 ohms would be one dominant module only 10800 ohms would be one non-dominant module only
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Old 02-06-2012, 08:06 AM
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Re: Replacing BCM on Grand Cherokee 2.7 CRD Ltd

Hi Frank,

thanks for your very informative reply.

I think I'm going to need to get my hands on a 'scope to do this job properly. I did try doing it with a Digital Voltmeter (DVM) but am reliably informaed by an electronic engineer customer of mine that DVMs average their readings over seconds so the readings can only be indicative, rather than definitive.

I managed to do the voltage checks as suggested by disconnecting a few of the control modules: - BCM, both door modules, EVIC and PCM.

I have been unable, however, to find the AZC Control Module which is particularly annoying because I have a feeling, as the AZC system is malfunctioning, it may be this module that is causing the problem. It is the only sub-system that doesn't work properly immediately after a system reset.

The only information I have found in the manual is "Left Side of HVAC Housing" with helpful comment "N/S" meaning "not shown".

I'm particularly looking for the AZC Module C2 white connector (12 way) that carries the PCI bus on Pin 8, so that I can disconnect it and check the PCI bus voltage with it disconnected.

Can you point me to it?

Cheers

Tony N
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Old 02-06-2012, 05:01 PM
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Re: Replacing BCM on Grand Cherokee 2.7 CRD Ltd

The AZC module should be part of the AC control panel. Did you check behind it for the connector?
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Old 02-10-2012, 03:02 AM
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Re: Replacing BCM on Grand Cherokee 2.7 CRD Ltd

You can isolate the AZC at the Diagnostic Junction Port, there you can isolate and probe most of the other PCI modules as well.
Not sure if yours is the same but in the US JGC the DJP is located under the dashboard to the left of the steering column. The DJP has a shorting plug attached to it.
Once you get to the DJP you can isolate a particular module by covering the shorting plug pin so it does not contact the particular module.

Attached is a diagram of the PCI circuit and DJP for a 2001 JGC hopefully it will give you an idea how the DJP is wired.

By the way, in my particular case, when I checked the signals with the shorting block removed from the DJP all looked good even using the oscilloscope. Turns out some of this modules only fail when they are loaded with other modules, which can be as low as 500 ohms with all the modules plugged in.

What I ended up doing was to build a little jumper block that would allow me to selectively start adding one module at a time.

In my case I found the PCM to be the problem, without any other module the peak voltage was around 6V, but it would drop as soon as I added another module, with all the modules plugged in the voltage was marginal at around 4V.

Hope this helps.

James
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File Type: jpg JGC_2001_PCI_bus.jpg (206.4 KB, 17 views)
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Old 02-10-2012, 01:03 PM
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Re: Replacing BCM on Grand Cherokee 2.7 CRD Ltd

Hi James,

thanks for that info. Assuming I can find the DJP, which I couldn't an hour or so ago (getting a bit dark out there), and that it does exist on the WJ 2.7 CRD RHD what will I find? My guess is, based on the orientation of the pins, a 16 way male connector with a 16 way pre-wired shorting socket connected to it.

You're obviously some way ahead of me on electronics so, if you would be so kind: -

What does the shorting connector do?
Does it short all the PCI pins (1 thru 8 and 11) together?
Which pin is the 'master' or 'source' of the PCI bus? I would have guessed Pin 1.

What is the chronology of testing each module?

Do I start with the system in its 'failed state' or do I have to reset, connect one module and run until the system fails, or doesn't?

Or should I reset and have all modules connected and then disconnect one and run to failure, in which case the one I disconnected is not the dodgy one, then re-connect that one and disconnect another until I get to a situation where the system doesn't fail, in which case the disconnected one is dodgy?

I don't have a 'scope to accurately check the voltages and a DVM gives only an approximate indication.

Sorry if I seem a bit dense on this, I was O.K. when car electrics where just switches and relays, but this software driven business is somewhat beyond me.

Cheers

Tony N

I've just done, successfully, a "multo cheapo" repair to a broken blend door. I should have taken a picture, but being in a hurry, and not wanting to jump the gun before I knew it was successful I didn't. When I've finished fiddling with this PCI problem I'll do a separate post, with pictures or drawings. Could be useful.
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Old 02-11-2012, 04:20 AM
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Re: Replacing BCM on Grand Cherokee 2.7 CRD Ltd

Hi Tony,
Sorry I forgot to mention the DJP is hard to see without removing the dashboard cover that seats between the instrument cluster and the steering column.

See picture 6 here for instructions on how to remove the cover:
http://www.wjjeeps.com/hvac_ip_remove.htm

Look for a harness terminated with a double row connector, that goes nowhere since its capped with a white-ish plastic cap.
You can also tell by the multipe yellow/violet wires which are all the PCI signals.

The DJP plastic cap has a piece of metal inside with multiple fingers that shorts all the contacts in the DJP harness.

Here's an article that shows a picture of the DJP, albeit its hart to see since the author seems to have put some sort of test rig on it.

http://www.gearsmagazine.com/view.as...3-eadd826e7991

Regarding your questions:

- What does the shorting connector do?
It connects the PCI signals from various modules together.
If you unplug the shorting block from the DJP, the modules become isolated from each other.

- Does it short all the PCI pins (1 thru 8 and 11) together?
Yes

-Which pin is the 'master' or 'source' of the PCI bus? I would have guessed Pin 1.

There is no master, every module can talk to each other at any time, although usually only when the ignition switch is on.

Every module is supposed to listen before talking, when they don't the bus crashes.

- What is the chronology of testing each module?

In addition to the article link above read this one for some further details

http://motorage.search-autoparts.com....jsp?id=668789


- Do I start with the system in its 'failed state' or do I have to reset, connect one module and run until the system fails, or doesn't?
Or should I reset and have all modules connected and then disconnect one and run to failure, in which case the one I disconnected is not the dodgy one, then re-connect that one and disconnect another until I get to a situation where the system doesn't fail, in which case the disconnected one is dodgy?

Since you do not have a scope for now I would suggest to start by isolating one module from the DJP at the time.

Be aware that some modules are hardwired to each other ( see the wiring diagram ) and are not accessible at the DJP so for a thorough check you may need to manually disconnect those modules as well.

-I don't have a 'scope to accurately check the voltages and a DVM gives only an approximate indication.

In my case a DVM was pretty much useless since the problem was a weak output level rather than a short circuit.

If you ever find someone with a scope, just take a look at the PCI signal at the OBDII connector ( pin #2 I believe ) and you will see a train of square wave pulses that should peak at around 7V, but if a module is weak you will see some significant lower peaks intermingled with the good pulses. Then you know you have a bad module for sure and then you make use of the DJP to confirm which module is the faulty one.

-Sorry if I seem a bit dense on this, I was O.K. when car electrics where just switches and relays, but this software driven business is somewhat beyond me.

Unfortunately this electronic stuff is way beyond even the typical mechanic at the dealer, that's why fixing this issue can run you into the thousands at the dealer, so it may be well worth it getting to know how this system works, but it's definitely not for the faint of heart.

Best of luck.

-James
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Old 02-12-2012, 06:55 AM
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Re: Replacing BCM on Grand Cherokee 2.7 CRD Ltd

Hi James,

most helpful, many thanks.

Luckily the DJP is very easy to find on my RHD JGC, once the largest piece of trim under the steering column has been removed, which is something I had already done in order to better access the BCM. I don't intend replacing the trim until this problem is sorted.

Removing the shorting plug from the socket explains everything. What I intend to do now is remove one pin (the fourth) from a .156" straight pin header, solder the remaining pins together plus the removed pin as a floater to plug in Pin 11. I can then, by moving the header across one step at a time, (rotating through 180 degrees after 4 steps), isolate each of the Pins 1 thru 8 in turn which, hopefully, will tell me which module is the suspect one. Unless, of course, it turns out to be one of the hardwired modules!

I thought that, rather than go along the disconnect power, isolate a pin, reconnect, then drive the vehicle until system failure (or not), I could perhaps connect my DVM between Pin 2 of the Data Link Connector and ground. As I am only getting at the moment, with the system in 'fail' mode a reading of 0.6V to 1.5V (0.6V to 2.1V in 'O.K.' mode) doing this, I would expect, when I isolate the suspect module to see the voltage reading which on a 'scope would show pulses of 7.5V, to show random readings over a higher range. As the time frame of these pulses is almost certain not to match the integration of the DVM I wouldn't expect ever to actually see 7.5V but I may see some readings a lot higher than at present.

Does this sound as though it might work?

Incidentally, with the system reset and engine running, when I connect my DVM to the Pin 2 of the Data Link Connector the system very quickly goes into the 'fail' mode. Possibly due to the load put on the PCI bus by the DVM?

If I go on much more you're going to getting fed up with me. Sorry about this, and many, many thanks for your help.

Tony N
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