Let my 92 SC400 sit for a little too long, so had to jump start it. I noticed after doing this that the speedometer is not accurate. Up until about 25MPH it seems accurate, but after that it gets wonky. I can be doing 70MPH according to my Waze app, but the speedometer shows around 50MPH. Anyone have any information on what this could be? Everything else is working fine, so maybe this was unrelated to the jump start?

 

Unrelated. I’ve seen a few issues in 16 years related to jump starting, but if anything the issue was that your cluster completely discharged. The caps hold voltage and feed a micro-voltage to the cluster. Several issues can result from taking the cluster off the battery power. This is basically the same issue that has happened. Another example of these types of issues are taking the battery out long enough for the ecu to reset, then you find your car won’t run properly. The ecu memory cleared it’s cache and now it is trying to read from a bad MAF sensor that is sending it signals incorrectly. Many people have found they have a bad MAF by changing their battery. These electrical gremlins are common place with old vehicles. It’s one reason why i tell people to keep 12v applied when swapping batteries. No need in finding out your 20 year old SC is running off an ECU cache the hard way.

 

Random example of a simple issue of removing the cluster from battery power....... backlights all or mostly work and always come on. Removing the cluster and putting it back in ten mins later to find most of the backlight doesn’t work now. Cluster capacitors feed just enough voltage to the bulbs to vibrate the filament and keep it alive. If the filament goes cold, it will not restart when you turn the key on. Old filament is hard to start burning because it has high resistance. Turning the key on and smacking the dash above the cluster a few times jars the filament, creating vibrations (kinetic energy) and it usually comes back on. It’s action and reaction, balanced by the effects of age. The only way logic can be used with these cars, is by understanding the effects of time thoroughly and applying that to your diagnosis. .......hence why I Usually give the correct answer, but the hell with explaining it. Lol. If i tell someone the right answer and they tell me I’m wrong.......ok. . I told someone to look in the ice blue thread and read it to understand their issue and they spent two weeks posting his “revelations” about what he found out........which were posted in the thread 15 years ago that i pointed him to. I’ll sleep at night either way. Lol. So the point is your car has a combination of age, dependency on electrical continuity, and results of losing it’s “pulse” for a while while the battery was dead. You’ll have to fix the issue now rather than it hiding from you as long as it had power applied.

These are complicated cars for their time. They come with complicated problems.

 

Oh and super short answer on fixing...... pull the speedo motor off the cluster and replace the caps. There’s three on most models. They are tiny and soldered in, will have their ratings written on the side. If that doesn’t do it replace every cap in the speedo, but this is the first and most likely issue.

 

Hi O.L.T im not sure if ur active on this forum anymore more or not but ive been seeing ur diys for these clusters and climate controls everywhere and they have helped me alot thanks. Im not sure why more people are opting to get their ecus and clusters fixed professionally when all the info they need is widely available here. Thanks to your led strip tutorial i was able to fix the back lighting on my sc300s cluster. Well sort of the RGB strip white setting was more of a blue so I am waiting on a better led strip to be delivered. I was also able to recover some 92 led needles that still worked from the junkyard however they are flickering and from what I can understand this is a issue with the actual capacitor on the board. In another post u shared a picture of ur notes with the capacitor types for the cluster that need to replaced but im not exactly sure what to order from digikey. There are a ton of options like the tolerance etc if u can help me out with this it would be great I dont want to mess anything up.

 

No specs are Important other than the ones listed. the ecu takes 105 degree caps, everything else is whatever.