Bhughes33

Bought a repo RX300 on Saturday, which came with only 1 non fob key, so its just a shell with a cn1 chip inside. The battery was weak and it took jumping it, as well as a good while of cranking to get it started but did get it to start 3 times before buying it (for pretty dang cheap). It took a lot of cranks each time but I thought I had another idea of why. After getting it home I now see the security light never stops flashing and I can't get it started again.

So, I've

1) Charged the battery completely and it seems to be a perfectly good battery.
2) Disconnected the battery for a good long while to reset the ecu.
3) Tried leaving the key in the ignition for a while.
4) Used cheap scan tool to check for codes, there were none.

I then started to inspect the transponder ring, amplifier, and ecu areas. Someone else has been in here before so I'm guessing this was a known previous problem. Ecu bracket was missing a bolt, Amplifier plug was unclipped from it's bracket.

I ordered a used amplifier that should be here later in the week and I'm set to check continuity from amplifier to ecu after work today.

I can't currently find a replacement ring for the RX, will one from an IS300 work at least for testing?
Is there a specified resistance of the ring antenna or just continuity matter?
Is this possibly just a bad ecu since I'm not seeing any codes/CEL for bad ring/amplifier?

I've also ordered an eeprom reader with the plan to virginize this ecu and see if I can reprogram the key and get it to work, or at least use it for learning while a replacement ecu arrives and I virginize that one.

whats everyones thoughts? Bad ecu?

salimshah

Some times thing don't come across properly when a problem is described along with a possible solution. The problem description then keeps reinforcing the possible solution.

I am going to try my best to share my thoughts and if it sounds like "repeat statements" please ignore my post.

Imobilizer issue will allow unlimited cranking [battery/starter may give up] but the engine will crank but will not fire. The immobilizer essentially kills the spark to spark plug [this how engines are shut off for years and years]. Conclusive evidence is no spark while the engine can crank. I test this by pulling out the most convenient spark coil + spark plug and lay it own the engine block. Note lack of spark can be due to other reason too.

ECU error codes are essentially for emission reasons and they do share other conditions as well. First gen from the era when OBDII was mandated, so it is pretty basic. At that time Toyota/Lexus had their in-house checking method/ports/computers.

RX ECU are pretty robust. I would worry most about the 'unknown' fixes/attempts_to_fix by previous owner/mechanics. I would look for hacks/markings etc to get a sense of what was messed with.

Yes, having a set of master keys is a must.

Salim

Bhughes33

I forgot to mention, I did confirm no spark on cylinder 4 and 6 using, using multiple coil packs and plugs. there is def no spark. I'm glad to hear the RX ecus are not a known problem, I believe in some my of research I came across a model that had a common issue of ecu causing a similar problem.

I've been getting this feeling that I need to just swap in a different battery and try. Just because the current one spins the motor over well doesn't necessarily mean the ecu is happy with the voltage it's seeing. The battery in my truck is basically the same size and post orientation so I'll swap it in after work and maybe I'll get lucky.

The vehicle is needed for my SO ASAP so I'm more interested in getting it running right now with just the current key, as I know for a fact it will. (Drove it home 25 miles no problem after a lengthy test drive). This will give me time to get a spare ecu, virginize it, and new keys cut for it.

If the battery swap fails I'll move on to the ring and amplifier and not focus so much on the ecu for the time being.

Bhughes33

Swapped in a known good battery and still no luck.

checked 12v and ground at the amplifier as well as continuity from the amplifier to the ecu. All checked good.

I checked resistance on the ring/coil/antenna and got 1.4 ohms. No idea if that’s right or not because I can’t find what it’s supposed to be. But 1.4 doesn’t seem right to me.

salimshah

See if you can get hold of workshop manual.

Salim

maxSteel

All the manual says is for the transponder key coil check if there is continuity between terminals 1 & 2

Bhughes33

I found a thread for an IS300 where they mentioned the key coil ring was supposed to be 1 ohm. I’m going to assume the RX and IS coils are very similar (they look very similar at least. ) and say that I’m good. But I went ahead and ordered an IS 300 coil for testing purposes.

salimshah

imho it is a passive coil [wire loops]. Open/short would be clear fail. Variation in ohmage should not be a cause of concern. If it was an active sensor then this variation would certainly be a cause of concern.

Salim

Bhughes33

*TEMP FIXED*

I was left without parts to try so I was just kind of screwing around. I removed the antenna coil and then separated it from the clear light housing and then plugged the antenna back in. Put the key in, and still blinking light. But then I grabbed the antenna and moved it closer to the key and boom, light goes out and it starts up instantly on the first try!

after a bunch of trial and error I’ve determined that it just will not work in the stock location. It needs to be spaced out another 1/8 to 1/4 inch then it works perfectly. So I’m not positive if this is due to the amplifier or the antenna but I have a replacement amplifier coming in tomorrow to try and then an is300 antenna coming this weekend if the amplifier doesn’t fix it.

but the car is drivable now and I’m not regretting spending the money buying it.

hopefully if someone is in a similar situation in the future they will come across this thread like I did the dozens I found and it gives them something else to try.

I will update once I’ve determined the exact faulty part and have it 100% fixed.

SDee

I'm gonna tell you here. Since I acquired a hand me down in Dec 2020. 2002 rx300. Start with valve cover gaskets plugs and coil packs. Do not drive it if it's flashing check engine. I went round n round getting this taken care of before finally getting someone that knew how to work on this thing. OEM coil packs only. Unless you want to do it again. And. Again. Mine is still idling rough and im quite irritated. But. I've been following this forum now 3 years and was able to diagnose my issues on this forum. A godsend. I've just gotten a trans overhaul and still having trouble. Hoping it gets straightened out. Just trying to help here. Using my experience the last 3 years. It's been wild lol and sorry for the late post of you've got it taken care of and I've not seen it. May have jumped the gun.