Hey All,

As the title says, I have a CEL problem with my SC400, a very interesting CEL problem. I'll try to explain the exact issue and a little history about the car as best as I can.

• 1992 SC400 with about 107K original miles. I am the 4th owner, the previous 3 owners were all seniors and the car has an extensive laundry list of work that was performed on it.
• No issues with start up. Cold, warm, hot it starts up just fine every time.
• No check engine light during idle, additionally, no rough idle issues.
• No issues with power, or acceleration. Car has plenty of power and torque and has no issues shifting through gears.
• The gas tank had about 2-3gal of old gas in it (~2 yers old). I filled it up on 7/27 with fresh 91 and dropped a bottle of Lucasoil octane booster into the tank right before fill up.
• As I accelerate past 4000 RPM the CEL will slowly light up brighter as the RPMs get higher. Then when I come to a stop, or slow down, the CEL will dim until it is completely off.

Looking for some insight as too what this problem could be. As many of my CA residents may know I can't smog a car with a CEL. I want to try to get this problem sorted myself before I throw in the towel and take it to a shop.

Little recent history of the car. ​​​​​​
My SC400 has been sitting for about 3 years or so, with some intermittent startups here and there, due to some starting issues that I was experiencing in the past. I had the car sit because I didn't have the money to fix those problems that I thought were major. I tryied swapping alternator, fuses, and relays, but the problem simply turned out to be caused by a faulty battery. I replaced the battery about 2 years ago with a new one and all those previous issues went away (go figure!). I let the car sit, under PNO status, because I didn't have funds to fix some of the interior issues (door panels), and other stuff the car needed. While it sat in my garage, I left the car on a battery tender as to not have the same starting problems as before. Now I have the funds to get it road worthy (smog, tires, service, etc.) and I've run into the issue described above.

I'm not an expert about cars so any help, advice, or direction is greatly appreciated! I am willing to learn and get my hands dirty to try to fix these problems before taking it to the experts!

 

Read the CEL codes through the OBD1 Port on the left hand side near the footwear. You will be able to narrow down the problem with the code.

If you don't have a OBD1 reader simply use a bent paperclip as a hotwire and insert the ends of the clip in terminals TE1 and El. Stick it in then go for a drive or just rev it in P.

Use the link provided to find out your issue. Do some thorough research and come back if you can't figure out the problem.

https://us.lexusownersclub.com/forum...ode-retrieval/

 

Does this happen when you rev the engine car not moving or only when you drive?

 

There is no CEL stored. The CEL does not come on until 4000RPM, then it goes away.

 

This happens only under load after 4000RPM. Nothing happens when reving the engine while in park or neutral to 4000+ RPM. When the car hits the rev limiter (shifts gears) the CEL immediately goes away and then will come back once it hits 4000RPM, rinse and repeat.

 

Try driving it with the the paperclip in the port, try jamming it in, not too hard. Drive at 4k until the light shows up and record the code it gives?

Try cruising in Low, or Second gear with the shifter. If you aren't able to do that, turn off Overdrive (OD) and get the the last gearing and cruise at 4k.

This sounds like a sensor or frequency input problem from my little experience.

 

I'll try this when I get home. Fortunately, I have reproductions of the Lexus SC400 shop repair manuals so I'll be able to cross-reference the code it spits out, if it spits one out. Unfortunately, the shop manuals don't give examples/instances of this problem I'm running into lol.

 

I'm not sure if you saw but I've edited my last post to help with getting a better code reading at 4k rpms. I saw you said the code disappeared when shifting. Its involving the gear shifter & OD. If you didn't see it just refresh the page/thread. Cheers.

 

Update: It looks like the problem went away on it's own. After much test driving the certain CEL never came back. I think the ECU had to "relearn" everything since the car had been sitting for so long. I was able to get the car smogged without issue.

 

Hi I too have a 92 SC400. The 92's are the most problematic. Intermittent electrical problems can be the worst. My first approach would be to check all fuses and relays.
On my car the climate control unit stopped working entirely. Previous owner started to take apart the console and dash when it was just a fuse for the cig lighter all along. Go figure.
I once had startup problems with mine. Everyone and their Brother told me it was the timing sensor. After changing out the TS it turned out to be a cracked 12 volt plug going to one of the ignition coils.
Checking the codes is not a bad idea but with lights getting brighter with acceleration, sounds like a short or bad connection some where.
I do know SC's get a little glitchy on hot days after they warm up too.
Check ever bulb and feature, CD player, Power Seats, Power Antenna etc. If one thing is not working right on these cars, it can cause a world of **** else where.
The SC400 is like a high maintenance wife. After market parts and doing things on the cheap, that car will get very very *****y.
They call for a 750 cycle battery too. I would not advise anything less.
Let us know how you make out with this, we can use all the info on these cars. Paul.

 

Usually a CEL that comes on while driving but doesn't store the code right away is a misfire happening while driving (it blinks though, wont stay solid), but it should get bad enough at some point to store the code (and then stay solid).
I think you have an ecu going faulty, happens alot especially on the older models like 92-94 and when they are sitting. add moisture and heat etc.. depending on weather and they can act up pretty bad.
If that is the issue it usually gets worse the warmer the car and ecu get, hope that helps point you in the right direction.