Instrument Cluster Troubles
05-15-21, 08:22 PM
#1
Driver
Thread Starter
Instrument Cluster Troubles
Hi folks, new here. Just bought my first Lexus - a 1993 SC400. It needs some work. To start with the speedo doesn't work. I've read the forum posts about the motor being worn out so I started my first project. The car, conveniently, came with a "spare" - same year, same model, that I can pull parts from. Upon disassembling the instrument cluster, it appears there are 3 core pieces - the mainboard, the light board, and the front panel. Wanting to keep the odometer reading properly, and assuming this was stored on the mainboard, I opted to only swap the speedo itself, by pulling it from the front panel from the other car and replacing it. Same problem - needle moves up, but not nearly enough to accurately reflect my true stpeed. My guess is the speedo from the other panel I pulled it from is bad. (Or am I missing something here - like a sending unit?) But in so doing, somewhere along the line (I've taken the cluster apart and put it back together at least a dozen times now), the airbag light came on. So again, reading the forums, I shorted pins 3 and 4 on the bottom row of the diag port. Airbag light flashes, but then goes back on. Also, somehow along the way, one of the lights in the upper-right of the speedo gauge stopped working. Tried replacing (several times) - no go. I'm assuming an electrical problem elsewhere on one of the boards. This is now the least of my troubles - if I could get the airbag light off the speedo working, I could live with a half-lit MPH gauge.
Ok...at this point I'm ready to just hop on eBay and buy a new cluster. But I'm still hoping to keep the odo reading correct. So I have two questions:
I welcome your thoughts.
Thanks folks.
Ok...at this point I'm ready to just hop on eBay and buy a new cluster. But I'm still hoping to keep the odo reading correct. So I have two questions:
- If I buy the new, supposedly perfectly-working cluster, and I pull the back mainboard ONLY, replacing it with mine, will that keep the odo reading? In other words, am I correct that the odo reading is stored on the mainboard?
- If I do this, will that migrate the airbag light problem to the new cluster? In other words, where is the data saved that's telling the airbag light to come on? I'm fairly confident there's nothing wrong with the airbag because the light didn't come on until I started doing all this messing around with the cluster. I'd just as soon save myself a trip to the dealership to tell me there's nothing wrong with the airbag - simply put; I'm not concerned and I want that light to go back off.
I welcome your thoughts.
Thanks folks.
05-16-21, 07:39 AM
#2
Hello Ethan and welcome!
Honestly these are fairly common issues with SC300/400 clusters. The best place to send them out to for service is Tanin Auto Electronix. They can repair and/or replace worn out speedometer and MPH gauges and they can also repair burned out needle illumination. They can also correct the odometer reading for you while the cluster is in for service. No, if you don't have the odometer reading corrected professionally the car will not reflect the mileage from the original odometer. It will just display the mileage from whichever cluster you happen to have installed.
The airbag light is tricker and that is something you seem to have been close to solving but it's just very difficult to get the timing of the taps on the diagnostic port terminals at EXACTLY the right rhythm, spacing and speed so that the ECU and Airbag ECU are okay with it and finally cancel the Airbag CEL light.
I have done it once myself and what I did was to use a Mac laptop and iPhone running Facetime to see the ODO from the engine bay on the screen. Both devices were running on WIFI. I placed the iPhone very carefully so that the camera could clearly see video image of the light. There was a very slight video delay but it worked for me. You could do the same thing with two iphones or an automotive boroscope (if you can get the snake cable's camera end to hold still and balance) or you can do it with pretty much any video camera hooked up to a monitoring screen. Whatever works so that you can see that little dash light while you try to get the correct and precise rhythm and speed of the terminal taps correct to the ECU's liking.
It's a very annoying process to go through yourself but the alternative is taking the vehicle to a Lexus dealer and having them cancel the airbag light doing exactly the same thing for a big chunk of money.
The way to avoid this in the future is simple but inconvenient: never turn the ignition to even the Accessory position with any part of the dash instrument cluster disconnected. So long as you never energize the car's electrical system with your key while the cluster is out it will never happen. Well... maybe also if you also have the steering wheel's airbag center disconnected and also turn the ignition key to Acc or start the car.
Honestly these are fairly common issues with SC300/400 clusters. The best place to send them out to for service is Tanin Auto Electronix. They can repair and/or replace worn out speedometer and MPH gauges and they can also repair burned out needle illumination. They can also correct the odometer reading for you while the cluster is in for service. No, if you don't have the odometer reading corrected professionally the car will not reflect the mileage from the original odometer. It will just display the mileage from whichever cluster you happen to have installed.
The airbag light is tricker and that is something you seem to have been close to solving but it's just very difficult to get the timing of the taps on the diagnostic port terminals at EXACTLY the right rhythm, spacing and speed so that the ECU and Airbag ECU are okay with it and finally cancel the Airbag CEL light.
I have done it once myself and what I did was to use a Mac laptop and iPhone running Facetime to see the ODO from the engine bay on the screen. Both devices were running on WIFI. I placed the iPhone very carefully so that the camera could clearly see video image of the light. There was a very slight video delay but it worked for me. You could do the same thing with two iphones or an automotive boroscope (if you can get the snake cable's camera end to hold still and balance) or you can do it with pretty much any video camera hooked up to a monitoring screen. Whatever works so that you can see that little dash light while you try to get the correct and precise rhythm and speed of the terminal taps correct to the ECU's liking.
It's a very annoying process to go through yourself but the alternative is taking the vehicle to a Lexus dealer and having them cancel the airbag light doing exactly the same thing for a big chunk of money.
The way to avoid this in the future is simple but inconvenient: never turn the ignition to even the Accessory position with any part of the dash instrument cluster disconnected. So long as you never energize the car's electrical system with your key while the cluster is out it will never happen. Well... maybe also if you also have the steering wheel's airbag center disconnected and also turn the ignition key to Acc or start the car.
05-16-21, 04:09 PM
#3
Driver
Thread Starter
Hey KahnBB6, thanks so much for your response! I love forums - I've been in love with forums for as long as they've existed. What a wonderful manifestation of the internet. Anyway...
I'll rig something up so I can reset that airbag light. I'm curious if you know how to find the correct sequence that needs to be used to reset it?
As to my other question about the speedo, let me elaborate;
What I haven't tried yet is to put the replacement mainboard onto the back of my light board and faceplate/gauges. The reason I want to try this is to see if the speedo issue is in fact a problem with the speedo motor, or perhaps the mainboard itself - like maybe it's not sending enough voltage to the motor?
The other thing I'm curious about is where exactly the odo reading is stored. I'd really like to keep my odo reading (it's at about 93K) vs. buying a replacement cluster on eBay with a reading of twice that. So then the question becomes; can I buy a new cluster and just pop my mainboard onto the that cluster to save the odo reading? Or even, remove the specific chip with the odo reading from the board and re-solder it onto a replacement board. Do you (or anyone) know which chip holds the odo reading? What I'm wondering about is whether I truly have two bad speedos, or is it more likely my mainboard is just bad. I know these speedos are notorious for failing, but two? Is it possible it's been the board the whole time or is that highly unlikely? Everything else seems to work except the lights on the temp gauge.
I know that's a lot of "thinking out loud" but that's what I'm working with at the moment. I'll try popping the replacement board onto the back of my cluster and see if I still have the speedo problem. I'm assuming that will mean I lose my odo reading but perhaps, like I mentioned, if the speedo starts working with this swap, I could just swap the odo chips. Or am I just wasting time and there's no way this problem is caused by the board...?
I welcome any thoughts anyone has.
- Mahalo nui
I'll rig something up so I can reset that airbag light. I'm curious if you know how to find the correct sequence that needs to be used to reset it?
As to my other question about the speedo, let me elaborate;
What I haven't tried yet is to put the replacement mainboard onto the back of my light board and faceplate/gauges. The reason I want to try this is to see if the speedo issue is in fact a problem with the speedo motor, or perhaps the mainboard itself - like maybe it's not sending enough voltage to the motor?
The other thing I'm curious about is where exactly the odo reading is stored. I'd really like to keep my odo reading (it's at about 93K) vs. buying a replacement cluster on eBay with a reading of twice that. So then the question becomes; can I buy a new cluster and just pop my mainboard onto the that cluster to save the odo reading? Or even, remove the specific chip with the odo reading from the board and re-solder it onto a replacement board. Do you (or anyone) know which chip holds the odo reading? What I'm wondering about is whether I truly have two bad speedos, or is it more likely my mainboard is just bad. I know these speedos are notorious for failing, but two? Is it possible it's been the board the whole time or is that highly unlikely? Everything else seems to work except the lights on the temp gauge.
I know that's a lot of "thinking out loud" but that's what I'm working with at the moment. I'll try popping the replacement board onto the back of my cluster and see if I still have the speedo problem. I'm assuming that will mean I lose my odo reading but perhaps, like I mentioned, if the speedo starts working with this swap, I could just swap the odo chips. Or am I just wasting time and there's no way this problem is caused by the board...?
I welcome any thoughts anyone has.
- Mahalo nui
05-16-21, 07:11 PM
#4
Keeper of the light
iTrader: (17)
We have covered this beyond extensively. In the sticky or search for "true ice blue" in this forum and enjoy the multi-year long thread. If you're going in you can't go half arsed, you have to know everything. while I could answer the questions, it won't stop the things that are going to happen when you try to swap the main board, specifically right after you disconnect the cluster from power..... the fun begins. Even if you do nothing but plug it back up, it won't work right. .... but as a bone to throw, odo is in the mainboard..... and the speedo motor will work with just 3 capacitors replaced on the motor, as you'll see in the thread.
in fact here.......... freebie. https://www.clublexus.com/forums/sc-...-clusters.html
Yet still, your boards are not going to match your motors, there ARE different motors, and all this could be fixed with $5 worth of capacitors. So, get to readin. Good luck! ×
in fact here.......... freebie. https://www.clublexus.com/forums/sc-...-clusters.html
Yet still, your boards are not going to match your motors, there ARE different motors, and all this could be fixed with $5 worth of capacitors. So, get to readin. Good luck! ×
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KahnBB6 (05-17-21)
05-17-21, 12:02 AM
#5
We have covered this beyond extensively. In the sticky or search for "true ice blue" in this forum and enjoy the multi-year long thread. If you're going in you can't go half arsed, you have to know everything. while I could answer the questions, it won't stop the things that are going to happen when you try to swap the main board, specifically right after you disconnect the cluster from power..... the fun begins. Even if you do nothing but plug it back up, it won't work right. .... but as a bone to throw, odo is in the mainboard..... and the speedo motor will work with just 3 capacitors replaced on the motor, as you'll see in the thread.
in fact here.......... freebie. https://www.clublexus.com/forums/sc-...-clusters.html
Yet still, your boards are not going to match your motors, there ARE different motors, and all this could be fixed with $5 worth of capacitors. So, get to readin. Good luck! ×
in fact here.......... freebie. https://www.clublexus.com/forums/sc-...-clusters.html
Yet still, your boards are not going to match your motors, there ARE different motors, and all this could be fixed with $5 worth of capacitors. So, get to readin. Good luck! ×
It is a lot of very specific information to get into and has indeed been covered before in several older threads. Do thoroughly read through the thread link he's provided before doing anything further with your cluster.
Replacing exact match capacitors on the other hand is a fairly common practice with many old electronics components (but it must be done carefully with good technique and ESD-safe equipment).
.....
I don't recall the exact sequence for the SC airbag reset procedure right now but if you search for those words you will eventually find the thread that I learned it from about ten years ago to reset the issue in my own SC. Since that time I have simply never turned on or even hooked up a battery to my car while the cluster has been out for any service. Once the cluster has been reinstalled only then will I re-install the battery and insert the key into the ignition. With that policy I have never had that airbag light issue again.
The same goes for swapping over to any other Toyota-Lexus steering wheel and airbag: never hook up the battery or put the key into the ignition until whichever steering wheel and airbag is being changed to has been fully connected and swapped over (also the battery needs to be fully disconnected for around 5-10min BEFORE disconnecting any airbag connector... but I digress as this was only a footnote to illustrate the main point).
I recommended the specialist service since that is the easiest way to correct your cluster issues with the least effort. However you can do the work yourself if you research extensively to learn the ins and outs. Tanin among others provides some reconditioning parts such as new illuminating needles and other parts. But I would definitely NOT swap those main boards between your original and spare cluster as O.L.T. cautions.
Last edited by KahnBB6; 05-17-21 at 12:18 AM.
05-17-21, 12:23 AM
#6
Ethan, I did a quick lookup and found an older thread I commented in which references both the airbag reset procedure and my own method for doing it with video monitoring of the light from the engine bay as I described above.
https://www.clublexus.com/forums/per...9-air-bag.html
https://www.clublexus.com/forums/per...9-air-bag.html
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Ethan5150 (05-17-21)
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Ethan5150 (05-17-21)
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05-17-21, 08:46 PM
#9
Driver
Thread Starter
Temp Gauge Needle
Anyone know where a person can get a replacement temp gauge needle? Mine doesn't light up anymore. And yes, I've gone through the entire amazing O.L.T. thread on the cluster and yeah, totally awesome, but I'm just looking for a replacement needle (or a fix to the light not working). Can't find anything on eBay... Suggestions anyone?
93 SC400 automatic
93 SC400 automatic
05-18-21, 03:02 AM
#10
Tanin Auto carries a full set of replacement needle boards of their design for DIY repairs that they'll sell you. They're about $85 for all four and work in 92-96 SC clusters.
https://www.taninautoelectronix.com/...needle-boards/
https://www.taninautoelectronix.com/...needle-boards/
05-19-21, 11:57 AM
#13
Driver School Candidate
Don't personally try to repair the cluster. Replace it and send the removed for repair if you care. Before doing any more work bang the dash above the cluster with your hand. That may give you a temporary fix. I'm on my second cluster and need to do the hand job from time to time.
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