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Chrysler Repair/03 Chrysler T&C w/3.8 FWD Engine misses and gauges erratic


QUESTION: I replaced the trans w/ an updated 04 trans,ran well for about 2wks,then it started bucking on acceleration (Erratic engine miss and Speedo and tach going wacko.At times the engine would rev and trans won't shift from second to third.Then sometimes it would shift normally. Got codes saying possible ECM or BCM problem.we replaced both,and same thing happens(no change)a local mechanic seems to thing that it's a ground short somewhere in the wiring.Before we spend a-lot of time searching for this "short"I was wondering what your thoughts were on this problem.

ANSWER: Hi Bill,
It would be helpful to know what the present fault codes are. Turn the ignition switch: "on-off-on-off-on and leave on" doing that in 5 seconds or less elapsed time. Then watch the odometer window in the cluster to see the mileage reading to be replaced by 4-digit number(s) preceded by a P. Tell those numbers and we'll go from there. Also, please describe as accurately as you can the behavior of the speedometer and tachometer. Do they both go wrong together and then run normally together? Does the engine miss and/or the transmission go wrong together or separately, and is that also synchronized with the gauges going bad and then does everything return to normal?
Let me know as best you can the answers to these questions.

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QUESTION: Ok the code that shows is P1684,which I'm sure is from disconnecting the battery.So I start it up and the speedo is jumping to about 35MPH as I'm parked and also the shift indicator is flickering lightly and all letters  get the circle around them and then goes to one circle back and forth to full.Now the tach seems to be ok but the speedo jumps and it'll shift from 1st to 2nd and stays there,won't shift,a few misses from the engine especiall as I.m slowing and the trans is shifting back to first all the while the tach seems okay,but the Speedo and shift indicators are jumping.
By the way it.s a new battery in it.Also as the shift indicators are flashing I'm hearing a slight cracking (popping) from behind the clusteras they change back and forth.Never seem to go back to normal operation.
Thanks again for your help with this diving me crazy situation.

ANSWER: Hi Bill,
You are correct about the 1684. Do you happen to recall the codes that came up originally and led you to replace the pcm and bcm?
The transmission refusing to shift beyond 2nd gear is typically described as a limp-in mode which the tcm chooses when there is a fault that has been recognized and so to minimize further problems it disconnects the transmission control relay so at that point only 2nd gear/reverse will work. If so there would be a trans fault code stored in the tcm which you can get only by using a plug-in code reader so the shop would do well to see if that is the case. However, the self-diagnostic readout should also give you a visual P0700 were that the case.
As for the speedo and the trans gear selector issues, those could be either a problem with the instrument cluster or a problem with digital information about the speed (which comes from the pcm) or the gear selection (which comes from the transmission range sensor and then to pcm, and finally both those signals are sent digitally from the pcm to cluster. Those data arrive on a white/violet wire on pin 9 of the cluster plug, and it may be that the solder joint between the pin 9 socket and the circuit board is "cold" and needs to be reheated with a soldering pencil.
I would start with a cluster self-diagnostic test:
Press and hold the odometer reset button, then turn the ignition switch to the "accessory" position (the one counterclockwise from 'lock', then release the reset button. Then watch the odometer window to see what messages appear in it. It should finally display 'end'. Then let me know, and I can tell you the possible causes of the issues with the speedo and gear indication once we know if the cluster itself has no problems.
The popping sound from the cluster suggests that there is a loose connection or something similar with its function so let us see what you find by these tests.

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QUESTION: Hi Roland,Sorry I didn't get back to you sooner,but to give you an update,we changed out the speed sensor on the trans and that took care of the erratic speedo and trans shifted good,until it warmed up and the engine still has the miss,and we could hear the clicking from the fuse box,and the safety shut down relay was warm and clicking and the shift indicator was flashing again as the clicking was going on even after we shut the engine off.
Now I feel like an idiot because I forgot to tell you that it has an aftermarket remote starter installed when the car was new it seems,(was in with the original papers)has a 144K now.So we're thinking that is what's causing the relay problem.The miss in the engine after it warms up,is close to what would happen if a person shut  the car off and back on real fast.What do you think on this?
Thanks again,
Bill Z

Hi Bill,
It would help to know what various devices are actually clicking, beside the autoshutdown relay. That relay is powered by fuse 16 in the power box module. Usually what shuts it off is the loss of signal from either the crankshaft position sensor or the camshaft position sensor which report that the engine is no longer rotating so it shuts off the spark and fuel to prevent a fire. There is no fault code from either sensor however.
That relay might be bad for example, or the wiring of a position sensor might be flakey, but that should set a fault code I would believe. But its clicking would certainly be similar to turning off and on the ignition switch real fast. So check the fuse and wires around the socket for the relay if accessible. The relay is controlled from pin 67 of the number 2 plug at the pcm, and it does that by either grounding that pin 85 of the relay socket (rear right pin) or leaving it float.
The power from fuse 16 arrives on pin 86 of the relay socket, and also pin 87, and when the relay closes it connect pin 87 to pin 30, which then powers the spark and fuel. Try substituting another relay for the autoshutdown to see if that does anything helpful, and in not, then try to check the voltages on the 4 pins of the socket.
Once you understand that situation the other issues may be addressed.

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Roland Finston


Get a Free Fast answer to your repair question about a Chrysler/Dodge/Plymouth car, minivan, SUV, or truck. Problems with electronically controlled engines and transmissions as well as body wiring problems are my specialty. This free troubleshoot advice forum helps you diagnose faults, minimize repair costs or do-it-yourself.

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I have do-it-yourself experience (50+ years) and a library of 100 1982-2012 Chrysler factory shop manuals and 20 multi-manual Chrysler Corp. CD's.

I was voted "Top Expert" 2010-2015, here at AllExperts, and have answered 20,000+ questions.


Five decades as a 'do-it-yourselfer' on domestic and imported cars.

Yahoo Autos Group called The Chrysler Lebaron Club (co-moderator)

Advanced degrees in Physics/bruised knuckles

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"Top expert" of 2010, 2011, 2012, 2013, 2014 and 2015 here at Allexperts. Quickest "average response time" at Allexperts (currently no. 1).

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