QuestionMy 2001 T&C LXi (3.8 L) has Speedometer and Tachometer needles jumping, and speedometer needle getting stopped on the wrong side of the post, making it impossible to know how fast I am travelling. The Tachometer jumps when the engine is cold, and the engine almost cuts out when it does this. The speedometer jumps as I put the car into gear, and jumps at each gear change. Again, mostly when the car is first started and is cold. It will lock the doors while it is in park. My mechanic has been trying to figure this out. He replaced the input and output sensors and this helped for a short time, but now the problem has returned. He said when the doors lock while the van is in park, the van thinks it is going 120 miles per hour! The van is running well otherwise. I am a single Mom on a limited budget. Any help you can give me to find a solution to this problem would be much appreciated. I can't afford to be without my van, but I can't afford to keep sinking money into it either. Thank you so much!
Sincerely,
Mary Lynn
AnswerHi Mary Lynn,
It is the sort of issue that comes up pretty regularly. In fact an ealier questioner with a van that was similar but not identical in its problem (that manifested itself in the driveability and the instrument cluster) just dropped me a note this morning. He had looked over the internet for a solution to his situation and concluded that it was a problem with the circuit board of the instrument cluster which when it suffered a poor connection to the data distribution system (called the 'bus' which shares data between the engine, transmission, and body (BCM) computers and the cluster) causes not only a cluster display problem but also a functional problem with the engine. He solved the problem by removing the cluster and finding there to be a poor connection between the plug socket and the circuit board in the form of a "cold" solder joint. The fix for that is to reheat all the solder joints at that interface with a solder gun or solder pencil so that the connections are restored firmly.
I will paste in his letter and the history, at this point:
"Hey Roland, I figured out the 98 caravan van a while back(details below) and was cleaning out my inbox. The no start condition was caused by an intermittant connection in the instrument cluster confusing the BCM. There were cold solder joints to the main connector pins inside the instrument cluster, and the two large resistors. I resoldered/reflowed teh connections and the van is fine now. The problem was fixed with only Labor!
Pass on the love,
George
Roland Finston <rfinston@hotmail.com> wrote:
Hi George,
I skimmed the 95 messages and am confused too about whether there is a single answer to this sort of problem. I suspect not. One report back that I thoght was interesting as regards the apparent false alarming and consequent 'start/die 3x behavior' was that there were internal electrical connection problems in his battery that caused electrical spikes that apparently disrupted the bcm function. Solution was to replace the battery. He found this by attaching a recording voltmeter to the system which captured the spikes. Another owner reported his similar problem was due to a poorly connected wire on the + clamp of the battery.
At this point, those are the only other ideas I have to offer.
Roland
--------------------------------------------------------------------------------
From: George <georgewahlgren@yahoo.com>
To: rfinston@hotmail.com
Subject: Found you on Experts...98 Grand Caravan
Date: Tue, 14 Nov 2006 20:42:00 -0800 (PST)
I read numerous answers you have given (found your email in an old post) and you seem very thourough. I was just taking a chance that you may have heard responce back from someone else reguarding these issues. I am an Engineer and a decent mechanic both mechanically and electrically, so feel free to give me the good stuff. ;)
At a minumum you will enjoy the reading on the link I provided, pretty crazy stuff.
I am working on electrical gremlins in a 1998 Grand Caravan with a 3.8L engine. I have found literally hundreds of problems just like mine on the internet with no definitive answer. I believe that most people figure it out and don't go back with their findings. The link below is interesting reading on the topic. It seems as though there are very systematic problems with this model, and that the dealers are just pushing BCM's on people which do not fix the problem.
http://www.topix.net/forum/autos/dodge-grand-caravan/TPC8IH1LI2S41I22D
The gages are flakey and loose power intermitently, and there are intermitent start problems that for many cases, happen associated with the gage problem. Sometimes it seems alarm related. There is a fuel shutoff three times and them the car locks down the system until a certain reset time has been passed.
My car has almost all of the symptoms noted the the link. I plan on cleaning the electrical connections to the cluster with some de-oxit D5, and then making sure my voltages are good, and that the battery cables are all healthy. Once and a while it seems someone had success with these cheap fixes. I'm really hoping that in your travels it has been traced down to one thing.
Thanks for
reading!
George"
So that might be the next thing to try: remove the cluster and with a soldering pen re-heating each of the solder joints at the interface between the circuit board and plug socket to see if that is what is causing the "gremlins".
Another quick diagnostic, although I can't be certain that it will be a true test, would be to just unplug the cluster and see if some of the driveability problems disappear (the door locks, the gear change harshness). It is not a fix, but it would lend support to the problem originating with the cluster itself if that were the case.
There is also a possibility that the misbehavior has been recognized by the self-diagnostic capability of the bus by having the system readout for stored fault codes in its memory. That is done with a diagnostic reader and there are indeed codes for problem related to the functioning of the bus that might then lead to the solution. Some autoparts stores will do a readout for free (Autozone for example) or shops will often advertise a "special" to do such a readout for $39 or thereabout. If you happen to have tried the "driving with the cluster disconnected" test, you will probably find a fault code in the memory along the lines of "communication from the cluster missing"; so to avoid that false alarm you might want to wait to do the test until after the readout was done.
If you make some progress or have another question please feel free to write back. Let me know if you get specific fault code numbers (four digits preceeded by a P) and any name that is mentioned to be associated with each.
Roland
