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2002 Lexus is300 Air con & water temp..multiplex issue?(GTE swapped)

4.2K views 10 replies 4 participants last post by  Malljz  
#1 ·
I have a 1.5jz running a standalone ECU for the engine and i opted to keep the stock ECU to retain my factory features(such as Coolant temp on the cluster, Air conditioning etc)

The car runs and drives amazing, just need to get these 2 last things sorted out......

So i have wired up both the A/C stuff and Engine coolant temp sensor, even went out of my way to weld a bung to the JZ water-neck to hide it and make it look nice... but the cluster isn't moving and the air conditioning isn't working.

I can lock the Air conditioning compressor by jumping the relay and the AC blows cold(so i know my wiring is good, i also put a can of R134 in the system to get the system at least started, i also checked all my wiring with a multimeter so i know its good). It seems as though the stock ECU (specifically the multiplex, BEANS language) is NOT communicating with the cluster(in this case the coolant temp) or the air conditioning controls...

Is there any wiring that i'm missing for the multiplex to work?



As of right now my E3 and E4 connectors are plugged into the stock ECU(completely untouched), my A/C Clutch lock sensor(E34 on plug E7) is wired into the ECU, and engine coolant temp is wired (to C24 on plug E5, one wire for the temp sensor is ground and one side goes to the ECU, correct?) & my airbags controller/unit is gone(not sure if this messes with the multiplex?)

Everything else on my cluster works(tach signal, speedo & even fuel gauge so im confident the cluster is plugged in all the way)


i dont know why it's not working, any help would be greatly appreciated.
I'm assuming something with the multiplex is messed up since neither the engine coolant temp works or the AC wants to work on its own...

Do i need to wire in any crankshaft or cam shaft sensors to the stock ECU to alert the Stock ECU that the engine is running? i can't find any information on this

(attached is the diagram i'm referencing in case anyone needs to reference what i'm referring too)
 

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#3 ·
I seen that, but was hoping i could avoid buying that if i really didn’t need to. I spent a significant amount of time moving my stock ECU behind the dash & keep all my wires intact with intentions of just keeping the stock ecu. But i’m not opposed to buying this since it’s a cheap simple fix!

This unit replaces the stock ECU right?


Will the factory Automatic climate control work with this? have you ran this unit?
 
#4 ·
I have not used it. I misread your initial post. You shouldn’t need the all4swap since you retained the stock ecu. I read it as you deleted the stock ecu, apologies. Since you moved the stock ecu to inside the car, I’d start with the wiring. Did you have it all working, and then when you moved the stock ecu inside, it stopped? Do you have pics of the stock ecu and its plugs - it’ll need them all to be plugged up I think.
 
#5 ·
Everything is wired up correctly & even if i did accidentally wire something wrong, at least 1 of the 2 multiplex things should work(either the coolant gauge or the air conditioning) . I read that when the multiplex isn't working properly those 2 specifically stop working so i’m confident my issue is with the multiplex(maybe the ecu needs an rpm signal or something to allow those functions to work?.. I don’t know)

i didn’t cut any wires to move the ecu inside the car. The stock ECU even triggers the fuel pump relay when i turn the key on, so i know its working as it should. There’s just something with the multiplex that’s either not connected or i’m overlooking. I wish there was more info online about this but NO one has made an article about it. Crazy how these swaps have been done for 20years+ and there’s no info on how to get it working.

I’m going to look into 1uz/3uz is300 swaps and see what people have done to retain their AC , maybe there’s some crumbs of info about the multiplex i can find there :(

rip
 
#8 ·
I’m running completely separate sensors for the coolant temperature. I’m running the OEM coolant sensor from the is300’s original 2jz-ge vvti, i even bought a 2nd OEM ECT(coolant temp) sensor with matching part numbers to check and see if maybe my old sensor was bad. I even boiled a cup of water & dipped the sensor into the water to see if the resistance across the sensor matched the OEM toyota/lexus number which is did. So i’ve verified the sensor works, the wiring is correct & connect per the wiring diagram i attached above in my previous post.


I am aware that splicing will cause issues(due to the fact that the stock is300 ECU measures resistance from the coolant sensor so splicing the wire increases resistance in the wire and throws off the reading).

Like i said above, it has to be multiplex related & i’m missing something related to that since both multiplex functions dont work but everything else analog(such as my rpm feed to the tach) works fine.
 
#9 ·
Unfortunately I'm no expert with the MPX/BEAN system; I've read enough about it to be dangerous.

That said, if you refer to pages 72 and 73 of the Diagnostics, Wiring and TSB manual for these cars - it shows MPX1 and MPX2 as orange and blue wires. Orange runs from the Engine Control Module to the body ECU, then to the Theft deterrent ECU, and then to the combination meter (instrument cluster). The Blue wire runs from the Engine Control Module to A/C control assembly, and then on to the combination meter.

Perhaps you've broken/disrupted the circuit somewhere between the ECM and the combination meter?