I have searched for this code 51 problem with no avail

[90mkiiisupra400hp]

Hey guys I don't know if anyone knows the answer to this, but I have a code 51 when my foot is off the clutch. If I press the clutch while checking the codes it goes away until I take my foot off again. I have read a ton of threads on code 51 and they all talked about TPS, A/C, and NSW signal in AUTOs I have not found any info on the NSW signal in manual trans cars setting off code 51. Now my car will NOT start unless I press the clutch, but what I am wondering is could the clutch start switch be going bad setting off the code 51.

I appreciate any help I can get

 

[jetjock]

... what I am wondering is could the clutch start switch be going bad setting off the code 51...

No. Do you have cruise control still installed? If so is it working?

 

[jonahs_supra]

http://www.cygnusx1.net/Supra/Library/TSRM/MK3/manual.aspx?Section=ST&P=12

and

http://www.cygnusx1.net/Supra/Library/TSRM/MK3/manual.aspx?S=FI&P=28

 

[90mkiiisupra400hp]

No I do not have cruise control hooked up anymore, and the car has always been a 5spd.

Thanks for the quick responses guys.

 

[jonahs_supra]

no problem
i just follow JJ where ever he goes

http://www.cygnusx1.net/Supra/Library/TSRM/MK3/manual.aspx?S=FI&P=55 tps test

JJ im curious to why you asked about cruise control?
please explain so i can learn

 

[90mkiiisupra400hp]

I have tested the tps 7 or 8 times lol and everything was in spec, but why would code 51 go away with the clutch pressed in?

 

[jonahs_supra]

i was thinking your clutch start switch is going bad
but thanks to JJ im pondering about the cruise control?

i know on my 87 the cruise control was removed...it was a manual...and had a code 51 but my tps was bad
on my 91 cruise control is removed due to busted cable...its a auto...no codes at all

i wonder what cruise control has to do with code 51 lol

 

[90mkiiisupra400hp]

I was thinking the clutch start switch was gong bad also but I guess that's not the case. I am also trying to figure out how the CC could set off code 51, hopefully JJ will enlighten us with more useful information as he always does.

 

[jetjock]

It would be better to simply meter the three ECU inputs to find which is responsible and go from there.

 

[3p141592654]

On M/T cars, the cruise control clutch switch is connected to the ECU NSW input. I don't have a M/T, but this seems like it could be WAD.

 

[90mkiiisupra400hp]

Well I am new at all this but I will try to figure out how to check the three inputs and report back on my findings. Thanks JJ and 3p for your help thus far.

 

[jetjock]

Well, you don't have to actually meter them. Just check 'em one at a time by manipulating each associated device (TPS and AC). By the process of elimination you should be able to narrow down whether it's the NSW input. Me, I'd just get in there with a meter because you're gonna have to anyway.

Re: Cruise control. I was referring to what 3p pointed out...

 

[90mkiiisupra400hp]

Ok so I finally was able to check a few things on the car today. First I checked the codes, and code 51 was still present. I pressed the clutch and code 51 went away. Next with the clutch pressed in and the code 51 gone, I hit the A/C switch to see if 51 would reappear which it didn't. Then with the clutch in and 51 still gone I pressed the throttle which made the 51 come back. I then let off the throttle and 51 went away again.

So what I have come up with, the code 51 is not activated by the TPS signal as it comes on and goes out when you press or release the throttle. There was no effect with the A/C button, and with the clutch released I have code 51 and with it pressed I do not have code 51.

Just an FYI, I have no A/C or cruise control.

 

[tyang82]

let me know what you find out. Im having this kind of problem also.

 

[Timmyd87]

take the bulb out. Just kidding. Kid at my work has the same exact problem let us know when you figure it out... Mine would randomly throw 51, replaced TPS and it stopped but didn't help his.

 

[90mkiiisupra400hp]

I am hoping JJ will come back when he gets a chance. It's just weird how the 51 goes away when I press the clutch. I think I am going to try changing the TPS again anyway because I was looking at some of my logs on the Maft Pro and noticed my TPS voltage is jumping all over the place, sometimes even below the .40 which is the base voltage when I am off the throttle.

 

[jetjock]

VTA voltage has nothing to do with code 51. Again, probing each input will determine which is at fault.

I should also point out this code, as long as it's not TPS related, will in no way effect how the car runs.

 

[3p141592654]

Just an FYI, I have no A/C or cruise control.

I believe that is your problem. With the CC computer missing, the black-yellow wire (color is for 1990 cars, yours may be different) that goes from the clutch sw to the NSW input on the ECU is floating when the clutch is out (it appears to be normally pulled to ground by the CC computer).

With your foot on the clutch the signal is pulled low through the starter relay winding (actually I'm not sure, could be through the theft deterrent, the TEWD is inconsistent and I don't have an M/T to check).

You need to pull that black-yellow wire to ground through a resistor (10kohm should do it), or put the CC computer back.

 

[90mkiiisupra400hp]

Thanks for the reply 3p, but the code is present when the clutch is out and disappears when the clutch is in. I think what I will do is try to track down the CC computer and throw it in to see if it goes away, and if that doesn't work I will give what JJ said a shot.

 

[90mkiiisupra400hp]

I thought I would let everyone know I figured it out. It ended up being the ECU. I changed it out and the code 51 went away and has not come back since. I have done about 300 miles since I swapped it out. Thanks for all your help in trying to diagnose this.