STORMINORM

1993 SC400, 95K miles, starts, idles, drives and shifts perfectly. Standard sized 225/55-16 tires, no CEL's (check engine light comes on, then goes off at starting, as it should).

Speedo consistantly reads 10-15 mph lower than actual speed. Dash cluster appears to be working just fine, nice and bright, smooth activation on speedo & tach, etc.

I'm told that if the CEL is not lit (in OBD I) there "should be no codes stored". Also informed that there are specific codes for VSS1 in dash (CODE 42) and VSS2 on transmission (Code 61).

Local dealer wants $120 to hook up to OBD I scanner: I can buy a OBD 2 & OBD I compliant scanner (with OBD I adaptor plugs for Toyota/LEXUS, Ford, etc.) for $199, but what is it going to tell me if there are "no codes stored" if no CEL?

Any help would be much appreciated: dealer service personnel had never heard of this happening.

Thanks in advance for your kind consideration!

p.s. Is there an accurate RPM to mph chart (presuming 4th gear as on the freeway) available? That would certainly help me avoid a repetition of Friday's "I clocked you at 71 mph, plus or minus 2" when my speedo was registering between 55 & 60!

SC400slide

iTrader: (11)

Could be a weak speedo motor, but with such low miles, I doubt it. Sounds more like the speed sensor in the tranny.

estomax

iTrader: (2)

if you look here, you can calculate all that
http://xse.com/leres/ss/calculator.html

you can put in your tire diameter and gear ratio, which for sc400 in 4th gear is .705 (lextreme) and 3.912 (google) rear end

should be at exactly 2000 rpm at 60

is the speedo off 10-15mph at 30mph and the same amount at 60mph? or is it a function of speed? if you have a smartphone you should use the GPS function on it to get your real speed and compare to the speedo. If you don't have a smart phone.. you should get one

Five0sc

I'm having similar prob. 177k on 92 sc. speedo reads low(10-15mph) noticed it comes up after driving a while. Search suggests VSS not sure which one, apparently there is two. My needle lights are out but have been for years. Needle still work just hard to see. Let me know if you find fix

STORMINORM

GPS / Smartphone speedo app shows 10 mph LOW at an indicated 20 mph, almost an actual 84-85 mph @ an indicated 70+!

Odometer seem to be spot on as it is still about 180 miles between our homes. Gas mileage still in mid 20's, depending upon how much is local vs. sustained freeway speeds so that kinda' rules out a tranny or differential swap (of which I have no knowledge nor any reason to suspect).

SC400slide: What is a weak speedo motor? Is there a part (# please!) that actually drives the needle?

Thanks!

p.s. Bought a COSTCO Magellan unit with free map updates forever, some AAA features (including a warranty extension from 1 yr to 2 yrs!) for $89.95 delivered to my home, so the exposure to additional speeding tickets due to being "unaware" is back to normal, whatever THAT entails!

Five0sc

Hey Storminorm, just had a buddy(owns a tran.s shop) hook up and scan my SC & drive it to check VSS, it checked out good. I/We are having same issue I believe. Indicates about 10-15 mph less than actual speed. Mine was 12mph off at 45 it seems progressive with speed (i.e. faster more incorrect) If VSS was failing, from what I've read, seem to give readings all over the place,high,low, inconsistant or just die. This is a ground problem in the gauge most likely. I've read where some have just cleaned & tightened screws in gauge cluster, some even made jumper wire to make a better connection. I just pulled mine I'll replace bulbs that are out & look in to retro to LED's (there's a lot of bulbs,I count 33 on cluster) Needles are pretty dead too so I'll see about fixing and/or retro to '96 needles maybe. have to do a search on here when time permits, Gotta watch your Q's on here lot of flaming.....does that make them flamers? Hummm... Hey I don't judge! To each his own Flame on! HAHA. Keep you up dated.

TaninAuto

Where does your needle rest at stop? On the zero line? Above it? Slightly below it?

I've seen low mileage needle motor failures.

Five0sc

I pulled cluster and replaced the 8 back lighting bulbs & replaced with Leds. Worked but not 100% satisfied, seeing some dim & brighter areas. (It's the leds I bought) ordered new types & color will see when i get them. BTW, they were "polarized" leds so had to plug cluster in to see if they were installed correct, had to flip the ones not lit.

On to the speedo..well, it was 10-15 mph slow. Did my bulb swap, cleaned & greased contact for screws on back and tightened now my speedo barely moves test drove around block up to 50mph (I guess) & it read maybe 20mph so... I don't know maybe speedo motor is toast? on the plus my Tach needle came back to life, I swapped it with speedo needle. My needle is resting pretty low it seems. I remember the Tach & speedo being pretty even but now my speedo is lower down at about the odometer first display, almost. Any help will be mucho appreciated.

Smokeygsi

I would say, if the Odometer is reading correctly then the cluster is getting the correct speed signal. That only really leaves the speedo motor and would be my guess

Five0sc

Well...fixed it. It was the speedo motor.Went to Pick a part and pulled a motor and needles from a 93 ES300 cluster, they looked the same, turns out they are. I also pulled a cluster from a 9/94 GS I found there. Same parts on that too, it was $36 bucks & $16 for the speedo-motor I pulled from ES. So in case you didn't know these other cars use the same parts. Speedo-motor part # 257695-025 same as my 92 SC400. I'm sure thats a Toyota number for these vehicles. Replacing isn't that hard, be careful not to bend the needle "stop" (that's why my needle sat low). The cluster has to be taken all the way apart & there's 2 phillips screws holding motor on the back of gauge face. Their a little tricky to get at due to circut board in the way, one more so. Make sure you pull needle off first. I still need a Tach needle & could use temp(tip is out) but for now I'm good. I'll check Ecology soon for es or sc/gs parts. If you do get a used motor make sure to clean the 2 spikes on the back, corrosion is definately on them after 20yr.s and those supply power to needle illumination & possibly ground for gauge itself. I used lithium grease after scraping them clean. Good luck.

STORMINORM

Thanks to all! Especially the p/n info which can be pretty hard to chase down.

pishta

Carefully on the speedo and tach needle swap. I can confirm 100% that the needle polarity, voltage to lights and even counterweight are different. Look at the numbers on the counterweight. I lost lights on my needles so I took voltage off pins I got 11 volts on speedo and 5 on tach. I used 3v led on tach and 12v led on speedo and they worked for about 2 weeks then both went dark and then speedo needle fell off as the plastic socket broke as it was brittle. Now the needle base doesn't even turn. I'll have to take it apart again and replace speedo needle again with a good base. I'm going to weight it properly so it just barely balances toward the needle side because if you don't the needles swing up when you shut the cat down. I'm getting very good at pulling that stupid gauge. Can do it in about 5 minutes now. Use a shorty and remove the smoked bezel with all cables still connected