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Old 11-02-2011, 06:54 AM
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Overhead computer display failure

Hi All,

hope somebody can help with this.

I'm reluctant to go to the sharks at the local Chrysler U.K. because they ripped me off last time I went there and they're bound to start talking in terms of new ECU/computer/engine/back axle and anything else they can think of to screw more money out of me.

Problem is this: - Our 2002 Grand Cherokee CRD Ltd is fitted with a few extras including the overhead computer display. Yesterday, having previously worked perfectly, this malfunctioned. I have lost the data on all of the displays that are related to fuel e.g. "Miles to empty", "Average (and "instant") consumption". The "Trip" and "Miles to Service" options still work. All [Menu] options are available.

The display I get on the setting I normally use is "---- Average Consumption", instead of a typical "26.7 Average consumption" and similar for "Instant consumption" and "Miles to empty".

I would have suspected a fuel sensor, but for the fact that the fuel gauge is still working O.K. and I have also lost, no matter what I enter using the [Menu] button, the light flash on remote lock/unlock, the door mirror resetting, the easy access driver's seat movement (and with it the seat memory setting), and the ability to set the seat position memory using the [Set], [1] and [2] buttons in the door.

Not only that, but, although the doors do lock, the lack of the usual LED illumination on locking would seem to indicate that the alarm/immobiliser is not working.

The normal electric seat and mirror position controls work O.K. so I know it's not anything as simple as a fuse blown. The symptoms are exactly the same using either of our 2 key fobs so I also know it's not a faulty key fob.

So what is causing this? Has anybody out there experienced this? Better still does anybody know an inexpensive solution --------- Please!

Thanks in advance,

Tony Norton
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Old 11-02-2011, 09:20 AM
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Re: Overhead computer display failure

Check all fuses that could be responsible, both under the hood and the dash, just in case. I would also check grounds. If there is a bad ground interrupting power it would reset those options. Another cheap fix, remove the negative battery cable from the battery for about 5 minutes. This will reset all onboard computers.

Well thats what I can think of for cheap fixes, now on to others. There is a body control module (BCM) that I believe is responsible for these functions, it might need to be replaced. The PCM is probably ok since it's more an engine management, this other stuff im pretty sure is run by the BCM.
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Old 11-03-2011, 06:32 AM
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Re: Overhead computer display failure

Hi Aaron,

you, sir, are a scholar and a gentleman, and I applaud you.

I tried the simplest, cheapest, option "...remove the negative battery cable from the battery for about 5 minutes..", and everything came back to normal.

First short trip out though, when I stopped and switched off, it went into failure mode. However, I went through the exercise again and situation normal was restored. I did think, whilst tightening up the negative clamp, that I might as well check the positive, and found that, whilst not exactly loose, it wasn't exactly tight either, so I nipped that up as well.

I'm wondering now if there was sufficient resistance at that terminal to reduce the power available to fire up a low current demand such as that required by a computer, whilst heavier loads such as lights, ignition and starter wouldn't have been affected.

Anyway, I've tried it half-a-dozen times since and everything seems O.K.

Many thanks for your help.

Best regards

Tony Norton
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Old 11-04-2011, 07:33 AM
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Re: Overhead computer display failure

Hello again All,

although the disconnect/reconnect seemed to work O.K. I guess that there is a dodgy earth connection or a component going down as soon as it gets a little warm.

The computer went off about 400yds from home this morning.

All I have to do now is find the damned thing.

Tony N
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Old 11-04-2011, 07:42 AM
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Re: Overhead computer display failure

Start by checking the grounds, there should be one screwed to the body by the battery. Make sure there isn't any corrosion on the grounds or battery leads, this will cause problems too. However, if this is the only component you are having trouble with it either has its own ground elsewhere or a component is failing. This about comes to the end of my knowledge, I haven't had to tear into any of those systems yet.
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Old 11-06-2011, 06:55 AM
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Re: Overhead computer display failure

Hi again Aaron,

If it hadn't been for your advice to check all grounds I wouldn't have found this.

I found that the ground wire, heavier black one, between the U.K. driver's door and the chassis had already been repaired some time ago. A good repair, not requiring any attention. I was using a digital ohmeter to check connection between black wire and chassis. AOK on all doors until....

....on checking the wiring to the tailgate I found a relay (see attachment) obviously an 'aftermarket' fitting used in connection with the towbar electrics. The ohmeter showed a direct connection from 12V to 0V on this relay which lasted a few seconds before going open circuit. The relay shows signs of water ingress thru the access hole to the potentiometer. I gave this pot a twiddle to clean it up, returning it to it's original position, and now, after a few miles everything seems O.K. with both the relay and the BCM.

If it goes again I shall know where to look, but meanwhile, in preparation, I intend to purchase a new relay at the enormous cost of 10 ($15) which will replace the old one, with suitable protection from water ingress.

A lot better result than $900 to $1000 dollars for a new BCM, and whilst you guys on your side of the pond are complaining about the cost of items such as this, spare a thought for those of us on this side. Anything that is priced in dollars in the USA hits the stores (particularly the stealerships) over here at the same figure in sterling, no matter what the exchange rate is!

Thanks again mate, hopefully all is now sorted.

Best Regards

Tony Norton
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Old 11-06-2011, 03:10 PM
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Re: Overhead computer display failure

Glad you found the problem! Hopefully it keeps working for you, good to know if it goes out again its only $15 to replace that relay. Good luck!
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Old 11-06-2011, 09:51 PM
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Re: Overhead computer display failure

If the EVIC panel problem returns, try to open it up and check all the solders on the circuit board. They tend to get loose over time, causing all kind of indication losses. Just re-soldering them again should help.
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Old 11-21-2011, 02:33 PM
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Re: Overhead computer display failure

@ Tony,
I have all your problems with a 2003 Grand cherokee 2.7 crd limited.(build date july 2002)
Electric windows don't work but mirrors and locks work fine. removing and reconnecting the battery lead works for a few minutes. As per your post, the overhead display loses all numbers, memory seats don't work, interior lighting, high beam indicator, but high beams work.
I looked through the wiring manuals and was thinking towards the BCM as it has an influence on all these problems. The driver door module receives an ignition status signal over the PCI bus from the Body control module. All these faults are actually caused by no signal from BCM over the Bus.( I think)
I know for a fact there is no relay fitted for the trailer. They are only scotchlocked to the tail lights but I'll have a look at the wiring. MAy I ask, what prompted you to look at the tailgate wiring. I have tried to look at this fault logically, but maybe that is where I am going wrong.
When I press the memory seat recall, the overhead display says "memory seat disabled, seatbelt fastened" This made me think that the drivers door module is talking to the memory seat module and the overhead display. Again seatbelt status is transmitted over the PCi bus by the BCM
I did have the broken ground wire in the door, but at this time none of the switches in the door worked.
I have also read that a difference of 2 volts between the signals can cause a fault, so this would make sense in your case.
Sorry for all the questions on my first post, but the Jeep has already been in with the dealer and no further forward. They say they need it for a longer time for more fault finding, so I'm very interested in your findings
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Old 11-22-2011, 11:35 AM
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Re: Overhead computer display failure

Hi Farmer,

all the symptoms you describe are, as you say, probably down to the BCM, but whilst mine was transient (the low resistance on the relay went to open circuit after a few seconds), yours appears to be permanent if the reset only lasts for a few minutes.

The general concensus was that dodgy BCM readings are quite often down to poor earth connections. Hence the advice to check the wires most likely to be affected by normal use. i.e. those between (a) the driver's door and the chassis, followed by (b) the passenger door, (c) the rear doors and finally the tailgate.

As I said, in a previous post, I found that the main earth wire to the driver's door had already been repaired. All the others were O.K. and when checking the tailgate I found the problem with the relay.

Having said that, I am not sure that I have totally cured the problem.

About a fortnight ago I fitted a new version of the relay I mentioned, and taped it up so the damp couldn't get into it. The car had been AOK since then, until......

Yesterday I wound down the driver's door window, to clear the condensation from the door mirror, but the window wouldn't go up! The BCM had gone down again, no readings etc. The discon/recon trick brought it back.

This morning, being intrigued by your comment re a 'seatbelt' warning, I tried operating the memory settings whilst I had the seatbelt secured to see if I got a message. No message, but lots of clicking, and the BCM went down again.

I now carry an easily accessible 13mm combi spanner and a piece of rag in the Jeep, just in case.

I am inclined to think that yesterday's hiccup was down to excessive damp, probably got into the door when the window was lowered, causing an electrical leakage. Mention of the PCI bus reminds me that computers and hostile environments don't mix. I spent 20 years sailing and, at the time, the best electronic equipment on the market was Brookes & Gatehouse. Their gear was all housed in hermetically sealed, nitrogen filled housings. I can't see Chrysler spending that kind of money when they can fit inferior Chinese equipment and then con customers into buying new for excessive amounts of cash. The stateside guys were quoting $900 to $1000 for a BCM, which translates into 900 to 1000 over here!

I can only suggest that, in the absence of a specific and obvious fault, you locate each of the Control Modules and give the housings and the connectors to them a liberal spray of WD40. The magic juice has been known to cure most things.

Cheers

Tony N
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Old 11-22-2011, 12:28 PM
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Re: Overhead computer display failure

I have already had the BCM module apart and all looks good. The PCB is covered in a clear silicone type lacquer to protect the pcb.
It is actually my Father's jeep, so I only look at it at weekends, but reading your post, I am now tending towards a wiring fault causing the module to lockout. All the "digital outputs" from the BCM work fine. All guages work etc, just seems to be the functions over the PCI bus.
I have actually earthered the 3 earth wires on the bcm to a bolt in the footwell, to rule out the splice between these wires and the earth bolt at the side of the handbrake. ( I can't find the splice easily, and I have a suspicion the 1999-2004 wiring diagram I have is not 100% correct).
I'll keep you posted on my findings and I'll have a look around the tailgate.
PS.I was pleasantly suprised at the price of a new seatbelt from the main dealer. 35+ VAT. I put a request on one of the breaker websites and I got a quote back of 75 for a used one, local breakers were all 40 for a used one. I also asked about the modules and they said anywhere from 50 to 500.
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Old 11-22-2011, 05:55 PM
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Re: Overhead computer display failure

Just one question Farmer. Where did you find the BCM on the 2.7 CRD?

I take it is a right hand drive one.

Cheers

Tony N
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