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Repair Questions and Answers.

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 #394408  by Johncsavage3
Okay guys, my low mileage 300m seems to have developed an electrical gremlin… So here’s what’s going on..

Car runs and drives fine. Cruise works without interruption, however the gauge cluster will begin going bananas until it goes to this screen. This photo was taken at 70mph. While it does this, the ATC will switch from auto to manual and defrost. The buttons will not respond to anything. The EVIC center doesn’t display any real data (instant mpg shows 0). The engine runs and drives fine. If I disconnect the battery and let it reset, it’ll clear up for the day, but returns the next day. Sometimes the seat will randomly move while going down the road also. I’ve swapped the cluster with two other working clusters — no change. I swapped a couple of headlamp switches and ATC heads with no change. Where should I go next? BCM? I’m seeing it’s a PCI bus problem.. I just hate to lose my low mileage odometer when I swap the BCM Thanks guys.

— also to note this begins by the airbag light flickering; then the fuel gauge goes to E, then everything lights up one by one and the gauges all go to 0

1999 Chrysler 300m — 43,000 miles

Codes 1687,1684,1695Image
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 #394409  by cin993
Bad ground cable a strong possibility.

couple of the things you highlight happened to my car while back... abs light on, trac light on, occasionally no start, atc unit resets, weird cluster stuff

AFter testing my ground cable, voltage drop, I replaced my ground cable from battery to strut post, problem solved. check your grounds
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 #394410  by TrepKing95
This is textbook PCI Bus failure. The Cluster displays "no buS", the gauges all drop out, the ABS, AirBag, MIL (check engine), lights all turn on due to lost communication. P1687 is "Lost Communication with Mechanical Instrument Cluster"; P1684 does not show as a valid trouble code in Chrysler Service Info, but might have a definition if read with a DRBIII Scan tool; P1695 Indicates that the BCM messages are not being received by the PCM over the PCI bus.

Does the concern only occur at certain speeds? How easily is it reproduced?

While the condition is present, take a multimeter and measure voltage between pin 2 of the OBD2 port (second from the top left, top is the wider side of the connector) and ground. Report back with your measurement.

I noted that you mentioned that the seat will randomly move while driving; I wonder if the Memory Heated Seat and Mirror Module (MHSMM) is failing and taking down the network. Easy way to tell is to unplug the module (located under the driver seat bottom) while the fault is active and see if normal operation is restored.
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 #394411  by FIREM
Welcome the best place on the planet to get assistance with your 300M. Collectively we have more knowledge than the factory ever had with these cars.
Good advice on both responses for some things to check. Be aware there are a few other grounds I would check. Base of the console, under the rug, at the accelerator pedal there are 2 grounds.
While PCI Bus failure is a potential, eliminate ant and all grounding issues first.
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 #394413  by LUNAT1C
I will echo Bob and Mike, check all grounds before proceeding with deeper parts replacements. Battery to strut tower ground cable (the jump point), body to engine grounds (one each side of the block), and the grounds Bob mentioned that are close to the accelerator pedal.

There may also be a ground to the floor underneath the drivers seat. I haven't checked that one myself, but I did see in the factory service manual diagrams references to a ground there for a number of systems.