Celica St205 Code 54 Issue - Not the Coolant Level Sensor...

JDM GT Four, ST185RC and ST205.

Re: Celica St205 Code 54 Issue - Not the Coolant Level Senso

Postby guile » Wed Dec 21, 2022 8:41 am

zaluss wrote:Not sure if this helps but I struggled trying to resolve this Code 54 issue and even swapped to another known good ST205 ECU with the same problem. Tried all the various relays, etc. I ended up using a Gen3 MR2 ECU which doesn't have the coolant level sensor problem and it's been good ever since.

I think the mapping is slightly different but works great.


I have a feeling it will be too good to be true if replacing the cap fixes it, I'm very hopeful though...

any ideas were i'd get a gen3 mr2 ecu please, do they have a different part number?
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Re: Celica St205 Code 54 Issue - Not the Coolant Level Senso

Postby underscore » Wed Dec 21, 2022 6:47 pm

93celicaconv wrote: I have a diagram view of the USDM ST184 C9 COR attached also, which is Toyota Part No. 85910-12010.


I tried one of those in my 185 RC and when the key was turned to ON the starter would engage. I'm not entirely sure how that happened but something was feeding power incorrectly. It didn't harm anything but it's something to watch for. The 185 relay 85910-30050 is still available, it was pretty widely used including in all 4th gens (not just the 165) and might match the 205 circuitry better.
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Re: Celica St205 Code 54 Issue - Not the Coolant Level Senso

Postby zaluss » Thu Dec 22, 2022 4:05 am

guile wrote:
zaluss wrote:Not sure if this helps but I struggled trying to resolve this Code 54 issue and even swapped to another known good ST205 ECU with the same problem. Tried all the various relays, etc. I ended up using a Gen3 MR2 ECU which doesn't have the coolant level sensor problem and it's been good ever since.

I think the mapping is slightly different but works great.


I have a feeling it will be too good to be true if replacing the cap fixes it, I'm very hopeful though...

any ideas were i'd get a gen3 mr2 ecu please, do they have a different part number?


Yes different part number 89661-17460. I would try the MR2OC facebook group or ebay.
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Re: Celica St205 Code 54 Issue - Not the Coolant Level Senso

Postby guile » Mon Jan 23, 2023 8:11 am

I'm very pleased to say that replacing the capacitor looks like it fixed the issue so I'm off to try and get it registered this Friday, YAY!

I treated myself to a very expensive new old grille with a very rusty TRD badge. I'm hoping to gently remove with a dremmel cut off wheel while trying not to damage the plastic...

IMG_0929-1.JPEG


IMG_0930-1.JPEG


IMG_0931-1.JPEG


a massive thanks to everyone for advice and guiding me in the right direction, this forum rocks!
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