Intermittent Speedometer Funtion - 1995 ZJ

[winstarman]

I just acquired my father's 1995 ZJ which is in excellent condition except for the speedometer. For some reason it will occasionally just "not work".

Here are some background details...

- Prior to me getting it the Vehicle Speed Sensor and cluster gauge were replaced by a mechanic in an effort to correct the problem- to no avail.
- When it works it's 100% accurate... when it doesn't it just sits on zero - no bouncing or craziness.
- There's no obvious rhyme or reason to it - you can be driving and it works, come to a stop and then when you start it doesn't work... then you go for a ways (few seconds to a few minutes) and it will just "wake up" and work fine and then perhaps cut out five minutes later.
- No Check-Engine lights
- Continues to shift just fine even though the speedo doesn't work.
- The odometer stops working whenever the speedo does and works when the speedo does.

I've searched the site but found nothing that I see as a smoking gun for my situation. This is my third jeep but I've never messed with a speedo problem. ANy help from the ZJ gurus would be appreciated.

Thanks in advance!
Richard

[fixer5000]

id say at this point you need to trace the wiring for the speed sensor. its gotta be intermittant somewhere along the circuit

[insane_drummer]

I'm in the same boat. I replaced my speedo sensor in the tcase, as well as the wiring plug for the speedo unit. Some days it will work just fine, others, it just sits at zero.

I have not messed with the cluster at all.

[winstarman]

More of the same continuing.... cruise works fine even when speedo doesn't.

If the problem was between the VSS and the PCM, I would be seeing other symptoms (i.e. CEL, shifting issues, etc), correct?

Given that the cluster and VSS have been changed out, I'm thinking perhaps it's an issue with the wiring between the PCM and the speedo, perhaps in the harness plug at the cluster?

I just wish it would either work fine or just stop altogether, at least that way it would be easier to troubleshoot.

[comanche freak]

I have the same problem. it appears to be the speedo guage itself. Others have said they fixed it by swapping clusters, one memebr said he fixed it by swapping the printed circuit board from the back of the guages, that way he kept his odometer reading. Ill have mine swapped in another month or so, im still rebuilding the rest of the jeep.
I seems to be the only logical answer when you consider that the odometer and cruise still work.

I justy noticed you said your odometer doen NOT work under these conditions, so it may just be a problem with the speed osensor, but i suppose it could still be the guage cluster that is the problem. On mine, the odometer continues to work normally.

[winstarman]

Yeah - the odo definitely does NOT work when the speedo fails.

The question is - if it's the VSS, shouldn't I see other symptoms? (others have made references to poor shifting or CEL with a failing VSS - or failing wiring from the VSS to the PCM for that matter.)

Any ideas? Can anyone explain how the VSS really works?

Here's another question - the PCM uses the VSS data to provide the overhead console's at-this-instant MPG data, correct? If that's the case and it's the VSS failing then I wonder if that will fail when the speedo fails? Hmm... guess I'll have to look at that.

Any further insight would be appreciated.
R-

[DaveG55]

For whatever this is worth....
I had the same issue on my '99 Neon. It turned out to be bad solder joints where the cluster plugs into the printed circuit board. A few mnutes reflowing solder fixed the problem.
It might be worth pulling the pc board off your cluster and going over everything with a good magnifying glass.

[winstarman]

I did confirm that when the speedo fails to function the MPG display on the overhead continues to function normally.

Are you talking about the PCB inside the gauge cluster, that's attached to the ODO?

[insane_drummer]

Reference from Chiltons:

[insane_drummer]

Ok, so I started digging last night...







All the soldering joints on the back of the speedometer gauge are perfect. Have people had problems with the flexible circuit board on the back of the cluster?

[comanche freak]

i did hear one guy say thats how he fixed it, just by swapping the circuit boards, he also indicated no visible damage to the board. I was thinking yours could be the connector issue because of the odometer not working sometimes.
Im eager to hear how this turns out as i will be diving into the same problem soon.

[winstarman]

Do you know if the PCB from the speedo can be swapped, leaving the odo as-is?

I've started to notice that it happens more when cooler outside, so it's starting to seem more like a cold solder joint. Sometimes getting up to a certain speed will cause it to come on, which also leads me to believe that it might be a weak connection and as speed increases the voltage in the circuit overcomes the internal resistance of the weak connection, causing the speedo to come alive.

Any thoughts? Advice?

[insane_drummer]

I just bought a part-out speedometer on ebay. As soon as it shows up I will be swapping the circuit board to see if that fixes the problem. All it takes to get the circuit board off is to pry the three white prongs away and pull up. It has some pins that actually connect the board to the speedometer.

Yes, you will be able to keep your current mileage if this works.

[winstarman]

Can you send me a URL for the part you purchased? I'm interested to see if that will resolve the issue.

[insane_drummer]

Quick call to the dealer and here's the info you wanted:

P/N: 4637888

The part is discontinued but you may be able to get it from a dealer in NY. Phone number is 1 (eight hundred) 456-6727

I will say though, it has a sticker price of $274 - you can buy a LOT of junk yard clusters for that price...

[DaveG55]

The circuit board may look perfect and still have bad connections / solder joints. If it were mine I'd get out a pencil soldering iron and start reflowing the solder joints. I'd pay particular attention to the connections where wiring harnesses plug in and be very careful around any IC's. You don't want to overheat those pins. That speedometerboard doesn't look that big so it shouldn't take too long and it might save you a dollars.

[insane_drummer]

There is a multitude of problems that could be wrong with the circuit board including capicitors, etc, not just solder joints. My joints are all filled very well, hence why im replacing my board.

[DaveG55]

Originally Posted by insane_drummer

There is a multitude of problems that could be wrong with the circuit board including capicitors, etc, not just solder joints. My joints are all filled very well, hence why im replacing my board.

Yes, there certainly are a multitude of parts. Caps, diodes, resistors, transistors, ic chips, etc. And yet the symptoms being described are intermittant and that best describes a cold/bad solder joint. If the electronic componants go bad they usually are bad and very seldom are intermittantly bad. Also it is entirely possible for a solder joint to be cold/bad and look perfectly fine - even using a magnifying glass.

All I'm suggesting is that the OP take 10 or 15 minutes and try something that could save him a bit of cash. It's free and if his board is bad, there's nothing to lose. If it doesn't fix it, buy a new one.

Buying a used board is a crap shoot at best, hope yours makes it intact and works well for you.

[insane_drummer]

swapped out circuit board and the problems are gone.



All you do is pry the little plastic holder arms apart and pull the board off. Swap, reinstall, you're good to go.

As stated before, obviously this is a gamble, but it worked for me.

[comanche freak]

great, thats what i was planning to do. I have a spare cluster ready to go.
thanks for reporting on the results