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The mkiv Supra Owners Club

Code 42 Fix


Dave

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My Odometer still increments the miles, so does this mean the speed sensor is OK and that the most likely culprit is the Odometer circuitry?

 

Yep, sounds like it. If you're sure you've wired in the speed converter OK (and if the odo is incrementing, it sounds like you have), then a flaky odo unit is the most likely culprit.

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Just a quick update...after enduring this issue for almost two years took the car to Envy and they resolved it within a day!!! Wish I had gone there at the start.

 

Needless to say I would recommend anyone with the same problem to contact Envy to have it resolved.

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JSpec: fixing the code 42 problem and wiring in a TSD are 2 separate jobs. Depending on the root cause of your code 42, I think some TSDs can fix the code 42 problem as a side-effect of installing them. I know my Thor TSD+DSC did. However, I realise that you don't want a DSC.

 

What make of TSD have you got?

 

If it were me (and apologies if you've already tried this), I'd remove any TSD you've got fitted, and simply bypass the odo buffering circuit (instructions around here somewhere on how to do this). Take it for a drive, and see if it fixes the code 42. If it doesn't, at least you know you need to look elsewhere (possibly the ECU connections). If it does, re-fit the TSD, making sure the fitting instructions don't re-instate the buffer circuit.

 

Some people don't like to chop into the wiring loom, but as long as you work neatly, any chops you make will be completely reversible with a bit more soldering and some electrical insulating tape.

 

Let us know how you get on.

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JSpec: fixing the code 42 problem and wiring in a TSD are 2 separate jobs. Depending on the root cause of your code 42, I think some TSDs can fix the code 42 problem as a side-effect of installing them. I know my Thor TSD+DSC did. However, I realise that you don't want a DSC.

 

What make of TSD have you got?

 

If it were me (and apologies if you've already tried this), I'd remove any TSD you've got fitted, and simply bypass the odo buffering circuit (instructions around here somewhere on how to do this). Take it for a drive, and see if it fixes the code 42. If it doesn't, at least you know you need to look elsewhere (possibly the ECU connections). If it does, re-fit the TSD, making sure the fitting instructions don't re-instate the buffer circuit.

 

Some people don't like to chop into the wiring loom, but as long as you work neatly, any chops you make will be completely reversible with a bit more soldering and some electrical insulating tape.

 

Let us know how you get on.

 

Ok Steve, thanks. I figured that was the case. I hear the most common culprit is dry solder joints on the odometer or the the output speed signal from the odometer being bad. Can't do it today, I had to fly and am already into the beer. :D

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  • 3 weeks later...

WAAAAAAAIIIIIIITTTTTT!!!! before you cut anything READ:

 

I've just completed this and happy to say my cruse is once again working!

 

BUT, there is no need to cut the pink wire, with a bit of fiddling round its not to hard to remove the pin from the harness and wedge it in the harness with the blue wire (for those of you who are perfectionists just use a glob of solder down there to hold it in firm and it will still be easy to remove later ). Don't stress to much if you break the pin as you should be able to get another one from dick smiths (radio shack?) or the likes.

 

i just used a tiny screwdriver (or a pin should even do it) squash the top of the end (the side that plugs into the ODO) of the pin in the harness and it should slide out.

If the end breaks you can crimp another end on later as long as you get it out

 

 

and DON'T forget to reset your ECU!

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scratch that, over drive light is still flicking and code 42 is back, at least it fixed the cruise control not working issue..... must have another problem too.

 

after visually inspecting the odo it looks in decent condition.

 

any other ideas?

 

the unplugging the pink wire as ive said above still works though.. would rather do that than cut the wire.

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This is the fix i did and all my troubles went away

 

 

Sounds about right Matt. I think this is what I said in post #39, but you've said it a lot clearer than I did! ->

 

If I'm correct, what you'll need to do is strip some of the insulation on the pin 5 wire, cut the wire to pin 6, and solder the loom side of the "pin 6 cut" to the exposed pin 5 wire. This merely bypasses the buffering of the odo unit.
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Does that buffering do anything? Surely it has a purpose. Will my active spoiler still work? What about the speed sensitive power steering?

 

When fitted correctly, the Thor DSC bypasses the buffer circuit. I don't think anyone's reported any problems caused by installing them. Can't really tell about long-term effects, but they seem unlikely to be caused by this sort of problem/fix.

 

Matt aero top's diagram joins what would be the buffer output (loom side) to the buffer input, whereas the Thor DSC supplies the buffer output (loom side) with a 1:1 (unbuffered unless the Thor unit duplicates the buffer circuit: unlikely) speed signal, and the buffer input is supplied with either a 1:1 signal (if you want the odo to keep counting in kms), or a 5:8 signal (if you want the odo to count in miles from now on).

 

The effect is the same for both changes: the odo buffer output is ignored by cutting the wire and leaving the plug-side unconnected, and supplying the loom-side with a signal derived directly from that supplied to the odo input.

 

I've got an NA so I can't comment on the TT stuff like active spoiler, but my progressive power steering works fine after fitting a Thor DSC.

 

Hard to believe I know, but I'm really not sure what useful purpose the buffer has. If anyone knows, please post it up here!

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As I understand it a buffer usually duplicates a signal, but from a source that can supply more current. You only need a couple of resitors and an NPN transistor to make a simple buffer circuit.

 

Its possible that the Odo circuit does some pulse-shaping, too. I did ask a while back if anyone knew what the waveforms looked like pre- and post-buffer. If they are the same shape and don't cross the zero volts line then it might be very easy to make a stand-alone replacement buffer circuit.

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I've done what Matt "Aero top"s diagram shows, however my overdrive light is still flashing, (cruise is fixed)

 

stevie_b you seem to know whats going on, any other ideas?

on why im still getting code 42 and the light still flashing, I even reset my ECU which fixed the issue until the drive after next.

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I've done what Matt "Aero top"s diagram shows, however my overdrive light is still flashing, (cruise is fixed)

 

stevie_b you seem to know whats going on, any other ideas?

on why im still getting code 42 and the light still flashing, I even reset my ECU which fixed the issue until the drive after next.

 

Not sure TBH. Does your car have a Digital Speed Converter or a Top Speed Delimiter fitted? These can sometimes give up and cause a code 42, because anything that was getting the speed signal from the DSC or TSD would now not be getting anything. If it's not an imported car, then that's almost certainly a "no".

 

My car's got a manual gearbox so doesn't have the overdrive toys.

 

I would follow the flow of the speed signal: check if the speedo still works. Then check if the odo still counts up the miles/kms as you drive. Does your power steering get heavier (as it should) when you go over about 50mph?

 

It could be loose wires around the back of the speedo dial, or around the odo unit. It's possible that the odo unit has dry solder joints (the joints have been known to give up after 13 or so years of use). This can be hard to diagnose though.

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Not sure TBH. Does your car have a Digital Speed Converter or a Top Speed Delimiter fitted? These can sometimes give up and cause a code 42, because anything that was getting the speed signal from the DSC or TSD would now not be getting anything. If it's not an imported car, then that's almost certainly a "no".

 

My car's got a manual gearbox so doesn't have the overdrive toys.

 

I would follow the flow of the speed signal: check if the speedo still works. Then check if the odo still counts up the miles/kms as you drive. Does your power steering get heavier (as it should) when you go over about 50mph?

 

It could be loose wires around the back of the speedo dial, or around the odo unit. It's possible that the odo unit has dry solder joints (the joints have been known to give up after 13 or so years of use). This can be hard to diagnose though.

 

not sure about the heavy... but the odo and speedo still work correctly I have the speed limiter removed by a SMT-6 piggyback chip.

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