Hello,

Thank you to all that may read this and help. I think my '92 SC300 is heading towards the dustbin as issues have been piling up this year but were all things that needed to be replaced anyhow. I have about 117K on it but its reliability is coming into question these days and I'm thinking about selling it for what I can. In any event, the car wouldn't start back in the spring, specifically the engine wouldn't stay on. The shop changed some module or sensor in the engine and it was fine up until 2 weeks ago when I couldn't get the engine to stay on. Revving the engine in park and quickly moving into drive seemed to do the trick but is probably not good for the car. However, if my foot was not on the gas constantly, it would stall so highways were best. I drove it to the shop earlier this week and it started right up. I'm not sure if it's the same problem from the spring or something else but I'm curious whether anyone has had similar issues and if they have any advice. Thanks!

 

Without more information, it is going to be hard to help much, sorry. The list of things that come to mind are: ecu issues, maf, vacuum line off, fuel pump ecu, distributor/cap/rotor. I would start with easy stuff, check that all vacuum lines are on and you don't have something loose on intake after the maf. Those can be checked in 5 min. Also check that maf, IAC valve, tps are all still connected completely. Those are also very easy. It starts getting harder from there. Has the 12v mod been done on fuel pump ecu? Has the main ecu been rebuilt? Check some of this and come back here and give us any other symptoms you can find.

 

Awesome. Thank you for your response. I feel like an oaf that I do not know what most of those things are and the car is at the mechanic's right now. An ECU was swapped out in the spring, not cheap, but I believe they took apart the fuel pump and everything else checked out at that point. I know that's not too helpful and I look like a Luddite.

 

No prob, gotta start somewhere. If it's at a shop make sure you come back and let us know what was found.

 

Thanks! It looks like you have the same car just about.

I believe it was the power train control module that was replaced in June. The car was also stalling unless the foot was on the gas pedal. I hope it's not something else.

 

The tittle says you have a check engine light (CEL), but I don't see that you specified what code is being thrown? If you haven't checked codes, you should be doing that before any guesswork troubleshooting.

PCM (powertrain control module) is the more technically correct term for the main computer (i.e., ECU, "computer," and other variants), as it covers the engine and transmission, in many cases. It also avoids confusion with other computers throughout the vehicle referred to as ECU's, such as the fuel pump ECU or mirror/seat computer.

 

Hey, I'm not sure what the code is. The main check engine light lit up on my dashboard. No idea what it's specifying.

 

As the others have suggested, you have to check it and see what code(s) the PCM (aka engine ECU) is alerting you to. Since your SC300 is a 1992 model year it has OBD1 engine diagnostics which has to be read manually without a conventional OBD2 code scanner.

It is easy to get the ECU to tell you what codes are being thrown. Go to the OBD1 engine diagnostic port on the lower dash on the driver's side just above the footwell. It will be round and gray. Open the plastic cap. Note on the cap's underside there is a label which tells you how to identify each pin. Use a paperclip and bend it into a a shape that can be inserted into TE1 and E1.

Have a notepad and pen ready.

Put the key into the ignition and turn it to ACC and then ON but *DO NOT START THE CAR*

Insert the paperclip ends into OBD1 port pins TE1 and E1. The CEL light will now begin to flash in a series of sequences. You will need to note how many flashes are in the first series before there is a slight pause and then how many flashes appear in the next series following it. If there are multiple CEL codes then after all of that there will be a longer pause and then a new series of flashes followed by another slight pause and then another series of flashes.

Each flash series adds up to a number before each little pause and then a second series of flashes adding up to a number.

Just for example: the sequence "Flash, flash... (short pause)... flash, flash, flash, flash" would mean 2 and then 4... or "CEL code 24".

After you wait long enough the sequences repeat all over again as long as you have the paper clip inserted into pins TE1 and E1.

If on the other hand you had two CEL codes then you would see something like this (again, a hypothetical example): "flash, flash... (short pause)... flash, flash, flash, flash........ (longer pause)......... flash... (short pause)... flash, flash, flash, flash" which would translate to CEL codes 24 and 14.

The code retrieval function only works as long as you have the paperclip inserted into those pins. You should keep it inserted until you're sure you're starting to see the very first code sequences all over again from the beginning before removing it. If you have to remove it mid-sequence for any reason (such as to write down the flashed numbers) then there is no harm done. Just re-insert the paperclip with the ignition key set to ON (but don't start the car) and you'll start from the beginning again.

Here is a key for the most common Lexus/Toyota CEL codes for OBD1 vehicles:

https://www.clublexus.com/forums/es-...ml#post3124723

 

Super helpful. Thank you. I mentioned this to the mechanic and they said it wasn't working so they're testing everything manually.

 

The check engine light isn't working? They should be starting with diagnosing that problem.

Was the mechanic unaware of reading the trouble codes and/or confirming the CEL lights up at Key ON, or did they just not mention to you that it wasn't working? One of the two scenarios, in addition to the first question, would have me looking for a new mechanic.

 

Ha yea. Well they're diagnosing it for free because they replaced the PCM this spring and it's under warranty. The check engine light is working but they said the trouble codes were not working, thus doing everything manually. Does that make sense and is it possible this could happen?

 

It does not make sense actually. If the physical bulb that illuminates the "Check Engine" symbol in the instrument cluster is burned out then that needs to be replaced with a new OEM bulb from Lexus (they last a LONG time).

If on the other hand the bulb is fine but the ECU, despite being repaired, does not register any trouble codes when you put it into the diagnostic mode I have described in my last post then that means there is still probably some issue with that ECU.

For it to be working properly it should be able to show you if there are zero CEL codes (when you attempt to check and it just blinks rapidly until you stop the diagnostic process) or if one or more error codes are active.

Unless they just do not know how to do the OBD1 code retrieval procedure or got my or other instructions for it wrong or unless the light bulb behind the "Check Engine" symbol is out or unless (very unlikely) there is a broken or cut wire between the OBD1 port and ECU.... then that means there may still be some issue with the ECU.

 

Okay thanks. So if the PCM is working properly, the codes will work properly then? If they are not lit up, then the PCM is not working properly, the very product under warranty and therefore that would be replaced free of charge, if I understand you correctly.

 

Like I said, looking for a new mechanic would be a high priority for me. Those are things that are easily referenced, and any competent mechanic knows it's an OBDI generation vehicle and where to go from there for diagnostics.

 

Ok thanks. Good points.