codes p1684, p1685, p1687 but car runs fine

moe8555 · Post by **moe8555** » Mon Dec 22, 2014 1:05 am

Hello all, long time no post (because the car has been fine)!

The other day, I was driving on the highway and noticed that the AIR BAG and CHECK ENGINE lights started flickering on and off every so often, with no rhyme or reason as far as I could perceive.

Then it completely went away for a few days and I thought to myself, OK, the car is a good 14-15 years old now so it could happen

But just yesterday, it came back and now the lights stay on nearly all the time (here and there one of them goes out for a few seconds and returns).

The key dance throws P1684, P1685, P1687. I haven't disconnected the battery lately, so no idea why P1684 shows.

I would like to point out that the car drives fine, no change in MPG, all electrical accessories work, and the cluster also works fine.

I'm thinking something is loose?

From my research, I see the following could be causes:
1) bad key(?)
2) bad ignition
3) loose connections somewhere (but where?)
4) bad ground(s)
5) MFS connector (mine isn't perfect, but it seems good enough)

Any other ideas??

moe8555 · Post by **moe8555** » Tue Dec 23, 2014 1:42 am

So this morning the gauges started acting funny, coming and going as they please.

I did a little more research and found a Mexican forum (and the help of a translation) where they wrote that it was a problem with the battery and had to discharge for 15 minutes to reset the BCM(?)

By the way, I'm assuming that all my error lights are false-positives because of the problem (I.e. Airbag) right?

Post by **occasional demons** » Tue Dec 23, 2014 5:56 am

Neons don't have a BCM. (Body Control Module)

Could be a bad ign switch, battery getting weak, a PCI bus issue, and/or a bad chipped key. Do you have another key to try?

moe8555 · Post by **moe8555** » Tue Dec 23, 2014 6:45 am

Yeah, I actually used my spare key this morning during the commute - no change.

I'll check the battery, it isn't the highest quality in the world and that solved the Mexican guy's problem.

Gnuserup · Post by **Gnuserup** » Tue Dec 23, 2014 4:01 pm

I guess there is something wrong with your clusters connection.

P1684 is common and might not matter this time

P1685 something wrong with your skim.
As you tried your sparekey, the module is left as one possible cause

P1687 no connection PCM to cluster (at least I found that on a PT Cruiser forum)

As you wrote about strange flickering of some lights first I guess it is the cluster.

Try to remove it and doublecheck it, esp. if something looks or smells burned on the plate.

Check the ground wires, maybe install another ground parallel temporarily and look if something changes.

Don't start without cluster or you get some more codes

moe8555 · Post by **moe8555** » Thu Dec 25, 2014 12:48 am

So here's another update:

P1686 has decided to join the party.

All fault lights except for low fuel and check oil now light up.

This happens within a few minutes of driving.

Upon starting the car, the first light to stay lit is AIRBAG, followed by Check Engine within 30 seconds.

This seems to be a gradual deterioration.

Does this new info help put us in the right direction?

Car still runs great.

Gnuserup · Post by **Gnuserup** » Thu Dec 25, 2014 5:03 am

Fuel is a separate sensor.

Your new issues makes me believe more what I stated before.

Get the cluster out and check it.
If you could, try a different one.

If you have access to a DRBII, connect it and look for codes, but I believe there won't be any.

moe8555 · Post by **moe8555** » Sun Jan 11, 2015 3:25 am

Just a little update, I'm still hoping for some "direction."

The problem disappeared completely for 3 full days and then came back with a vengeance.

This morning, for the first time, even my gas gauge started acting funny with the needle dropping and rising and causing the low fuel chime to sound every so often.

Do you guys think this is a bad cluster issue, or something more complicated with the PCM or wiring?

I did the cluster self test and it seemed to succeed....

Neons are too rare here so I don't have the privilege of going to the junkyard and getting another cluster. I would have to order from eBay and have no recourse for a refund if the cluster wasn't the problem.

Ramroid · Post by **Ramroid** » Sun Jan 11, 2015 4:42 am

moe8555 wrote:Just a little update, I'm still hoping for some "direction."

The problem disappeared completely for 3 full days and then came back with a vengeance.

This morning, for the first time, even my gas gauge started acting funny with the needle dropping and rising and causing the low fuel chime to sound every so often.

Do you guys think this is a bad cluster issue, or something more complicated with the PCM or wiring?

I did the cluster self test and it seemed to succeed....

Neons are too rare here so I don't have the privilege of going to the junkyard and getting another cluster. I would have to order from eBay and have no recourse for a refund if the cluster wasn't the problem.

Mine did the same thing, 02 SXT auto. Same issue you're having. I used an OBDI II computer dad has for his mechanic to clear the codes, and they havent come back. No issues as far as gauges. I'm not 100% why clearing the codes worked, it may have just been a hiccup in the PCM coding that caused the issue. Try to clear the codes and see if it helps, if not, swap out the cluster and see if that helps. I have 2 spare clusters you're welcome to. 00 se and 02 sxt clusters if you need them

moe8555 · Post by **moe8555** » Sun Jan 25, 2015 1:47 am

Just a final update on the matter for the sake of future searchers:
Believe it or not, but Ramroid's solution of clearing the codes did the trick!

So far so good. I guess we've found a bug in the PCM! Now just to find out what causes it to crop up, but I'd rather the problem not return again

So in short: always start with the small stuff before jumping in and taking things apart needlessly!