Odd instrument cluster behaviour

[Prostheta]

Ergh! Well, isn't it always the case that people bring problems eh?

Last week the confuser beeped whilst I was driving and dumped on the ABS, Traction Control and Handbrake lights. I noted a P1687 error on the OBDII reader which seems to correspond to "No mechanical instrument cluster bus message" (OBDII diagnostics. Trouble code definition for code P1687. Causes of error P1687). I cleared that and decided to see what would happen when I restarted the car. The error stayed clear, and then the lights reset to normal functioning a couple of minutes down the road.

So anyway, it returns and then it goes away with no rhyme and reason as to why. The P1687 code hasn't returned since I first cleared it, so I'm not even sure if they were related.

It's nice and icy this week so I had chance to check whether there is any sort of issue with the ABS and traction control; none. The handbrake light seems to behave slightly differently; when the weirdness occurs, the handbrake light only stays on and joins the ABS/TC lights when I use the handbrake.

It's strange, because clearing the OBDII doesn't touch the lights, so I don't think it's a code throwing them. Still, the lack of causation for when it occurs and randomly goes away is the strangest thing. They seem to be on more often than not at the moment, however I've sort of mentally blanked them out now.

Anybody else know of or have had this sort of fun and games?

[JonN]

I've experience similar things in a Silverado and it turned out to be a bad ground

[Prostheta]

Now that is interesting. Since I've never had to deal with a bad ground before in a car (plenty in amps and guitars though) I'm guessing that this will be a real adventure....

In a slightly-related issue, I've had the PCM memory checksum error since forever and I'm wondering if a bad ground is the source of that sort of chicanery (other than the faulty memory chips from that year)?

Either way, I'm going to need to get a plan together to locate any bad earthing. Hopefully there's some kind of logical approach to checking that....are we talking the main earthing point at the "front of house" or perhaps deep within the loom, or earthing points around the chassis?

That we have deeply-subzero temps right now and the fact this is intermittent seems to make this the most plausible explanation. Did you get any other weirdnesses in the Silverado when you had this or was it just the cluster?

[sawdust123]

I've had this problem and MANY other false codes over the last 6 months. This is pretty common on Chrysler products. My speedo will occasionally stop working for 30 minutes at a time while on long drives (but odo still works). The BCM is part of the instrument cluster. It handles, airbags, ABS, anti-lock brakes and other functions. If the signal to the BCM is bad, those functions automatically disable.

I believe the source of ALL my code problems relate to bad electrical connections in the engine. My first suspect is the grounds. There are many to clean. There are connections on both inside fenders and there are two to the engine block I believe. Some are really hard to reach, even if you are just trying to spray contact cleaner on them.

I have seen countless threads on Jeep and other Chrysler forums where people replace the BCM or PCM only to have the problems reappear.

BTW, I am an electrical engineer and I used to study signal integrity problems. These random issues have all the hallmarks of such a problem. I also know that your typical mechanic, even a factory mechanic, is not able to debug this issue. They just throw parts at the problem. If they are lucky, they will jiggle the offending connection during the repair and you end up with a few days or weeks of smooth operation after the repair.

[rob302]

wow you've been here a looong time!! quick off-topic question.. why the name "sawdust" if you are an electrical engineer? just curious

[Prostheta]

At the very least the problem is quantified. I can live with this going on until the weather thaws (-19°C/-2,2°F) before having a dig around the ground straps or whatever they are. As long as this isn't an inspection fail here, and that it won't involve me having to replace the cluster, great.

That also means I can concentrate more on the overhead console conversion and central console Android tablet install.

[wb2kki]

My cluster problems on my PT and Jeep water / corrosion in one of the connectors (leaks never found????) and a bad ign switch.

Mike
06 PT Basic

[sawdust123]

Originally Posted by rob302

wow you've been here a looong time!! quick off-topic question.. why the name "sawdust" if you are an electrical engineer? just curious

Because I like to work with wood but often the most tangible by-product of this hobby is sawdust. I'm am very good at generating it.

[Prostheta]

I'm a professional woodworker by day and guitar-maker by night. I produce the stuff at a prodigious rate.

I hate to get concerned over the problems that you experienced with your cars, @wb2kki but I've planned on doing a full cleanup in spring around the contacts and earthing points. This hasn't yet been done to the PT so I think she'll only benefit from it. Hopefully the bad ignition switch was a secondary problem, rather than one I should perhaps expect.

[wb2kki]

ign switch cured the problem for sure. And the corroded connectors were separate problems at different times. Since you got a code I would would google that code and follow that path.

Ign switch problems are common on these cars.