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tcm testing


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21 replies to this topic

#1 mountaingoatgruff

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Posted 18 December 2008 - 08:24 PM

i found my answer off-site. thanks

Edited by mountaingoatgruff, 18 December 2008 - 08:30 PM.


#2 mountaingoatgruff

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Posted 20 December 2008 - 01:35 AM

...but that answer didn't help. i'm trying to determine what's wrong but this car is really pissing me off - i don't have the patience or the money right now. at least i have the time though, been laid off for a month now.:mad:

the car runs fine and all except it shifts into 2nd late and neutralizes when it should be shifting into 3rd. trans is completely rebuilt: all new clutches (friction and steel plates, including mpt clutch), new 2-4 band, reman'ed torque converter, fresh fluid at proper level, new line pressure and transfer solenoids, new inner hub for transfer clutch, new atf strainer, and even a brand spankin new pan. in all, over $2000 for those who are wondering - buy a used or reman'ed... or even better, buy a m/t car!

i've checked the wiring and connectors and i can't find anything wrong in the harness anywhere.

i had a tcm code 31 for tps. replaced the whole throttle body with a matching one from a jy without disturbing the tps so i wouldn't need to worry about adjustment. old tps had a voltage signal from about ~0.5V to ~4.5V, idle to wot. replacement has a voltage signal of ~1V to ~5V. i installed the replacement tb, cleared the code, then started the car.

now its giving me a code 32 for vss1 and even after clearing the codes with my ssm, it still shows both codes 31 and 32 stored in the memory.

does the tcm usually give one code at a time even if there's multiple faults? is disconnecting the battery for a few hours enough to clear all codes 100%? how am i supposed to tell if the tps is working properly? since the vss1 is for the awd system, if i put the fwd fuse in shouldn't the tcm disregard it's input (so i can rule out that being my shifting problem)?

i wish my hatch were done already. i hate automatics, especially 4EAT's. i'm seriously about to wrap this damn pos around a tree.

Edited by mountaingoatgruff, 20 December 2008 - 01:39 AM.


#3 presslab

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Posted 20 December 2008 - 08:50 AM

So are you saying that when it should be shifting into 3rd the engine just spins freely?

Have you tried unplugging the TCU? This will cause the tranny to use 3rd gear with full line pressure, and a locked transfer clutch. If unplugging the TCU doesn't work then it's something hydraulic/mechanical inside the tranny.

Freewheeling in 3rd gear sounds like the high clutch is not working right.

Sorry to hear you are laid off, I just got another (albiet low pay) job after being out of work for 6 months.

#4 grossgary

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Posted 20 December 2008 - 09:47 AM

mountaingoat - unplug the wiring harness from the transmission and see if it drives like that. it'll be "locked" in 4WD and in 3rd gear but otherwise should run and drive fine. if it doesn't run right that way then it probably points to internal issues. if it does run fine then i'm guessing it could be internal/external to the trans.

#5 grossgary

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Posted 20 December 2008 - 09:50 AM

after i saw your other post it reminded me - make sure the pins are all okay in the wiring harness plug. make sure they're not bent.

#6 mountaingoatgruff

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Posted 20 December 2008 - 03:43 PM

So are you saying that when it should be shifting into 3rd the engine just spins freely?


yeah, that's exactly what it does. the engine revs freely for a few seconds and then it grabs again, sometimes its more than a few seconds. also, sometimes it works fine and sometimes it does this - but if you ride her hard the shifts are almost always just fine.

Have you tried unplugging the TCU? This will cause the tranny to use 3rd gear with full line pressure, and a locked transfer clutch. If unplugging the TCU doesn't work then it's something hydraulic/mechanical inside the tranny.

Freewheeling in 3rd gear sounds like the high clutch is not working right.


i haven't tried unplugging the tcm/tcu or the trans itself as gary suggests. i put it in fwd mode last light while checking different things. vss1 is apparently toast but the tps is working well. this has got to be either a wiring harness fault (hence my request for diagrams) or the tcm itself.

Sorry to hear you are laid off, I just got another (albiet low pay) job after being out of work for 6 months.


i was a machine operator at a non-union plant making $19.80/hr and now i've got my fingers crossed hoping for a $12/hr job that i won't hear back from till jan...

#7 mountaingoatgruff

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Posted 22 December 2008 - 12:28 AM

just wondering...

when i got the impreza, it had bad tires - 185/70's on the front, 175/80's on the back (iirc, i know they were different sizes front to rear).

i swapped over the tires from the totalled legacy before the wrecker came for it, brand new 185/70's.

both cars had 14" steel rims but stock size for the impreza is 175 while stock size for the legacy (what's on the impreza right now) is 185.

i noticed on my select monitor that the vss1 is reading one mph faster than the vss2. could this be because of the increased tire size and will this cause issues? if so, can i resolve the issue by using a legacy vss1 (i don't know if they're the same).

i very much doubt it's related to the problems i'm having but i just want to make sure it won't cause issues down the road.

as far as fixing what's wrong right now, the voltage signal from the tps is spiking while driving. i replaced the tcm with a 95 impreza unit and the vss1 with a used but working one. the neutralizing is gone but while driving, the tps voltage spikes causing the trans to downshift then upshift back and forth. i have verified the operation of the tps multiple times and its exactly what it should be. i think this has to be a crushed/shorting pair of wires or something of that nature. i'm waiting on motivation to tear the harness apart to find the culprit...

#8 presslab

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Posted 22 December 2008 - 12:59 AM

One MPH error at what speed? Probably no big deal. The front VSS speed is driven off the diff speedo gears. The rear VSS is off the "teeth" on the transfer clutch hub. Changing just the sensor should have no effect as long as both are working correctly.

Is the TPS in it the one from the junk yard? Maybe it is dirty, you can clean it with some contact cleaner. Radio Shack has some with a little lube in it; that's what I used when my TPS was dirty. Just spray it in there and turn it back and forth a bit.

http://www.radioshac...oductId=2103700

So how do you know the TPS voltage is spiking? Is this just inferred from the TCU downshifting erratically? Have you put a scope on it to see the TPS signal?

#9 mountaingoatgruff

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Posted 22 December 2008 - 02:36 AM

One MPH error at what speed? Probably no big deal. The front VSS speed is driven off the diff speedo gears. The rear VSS is off the "teeth" on the transfer clutch hub. Changing just the sensor should have no effect as long as both are working correctly.


its 1mph at all speeds that was able to check it (i was driving in the dark looking back and forth from the dash to the monitor). i have a subaru select monitor that gives the mph and kph readings for each speed sensor, 4 readings in all. while driving the car with the monitor hooked up, i verified that vss2 matches the speedo (of course, they're essentially the same unit driven as you say by the nylon gears on the front diff). vss1 gives a consistent 1mph difference at all speeds above a few mph.

Is the TPS in it the one from the junk yard? Maybe it is dirty, you can clean it with some contact cleaner. Radio Shack has some with a little lube in it; that's what I used when my TPS was dirty. Just spray it in there and turn it back and forth a bit.

http://www.radioshac...oductId=2103700


the tps is from the same jy 95 impreza the tcm came from, about 140k miles on that car. i swapped the entire throttle bodies and i cleaned the snot outta the 95 before installing it, it was quite filthy. i used brake cleaner and a rag, mostly focusing on the tb itself and i avouded getting brake cleaner in the tps. are you suggesting i remove the tps to clean it with contact cleaner? will i need to adjust it after that? i have contact cleaner already but i don't have adjustment specs for the tps so i've tried to avoid removing it. do you think that simply being dirty would cause the voltage of the signal wire to spike?

So how do you know the TPS voltage is spiking? Is this just inferred from the TCU downshifting erratically? Have you put a scope on it to see the TPS signal?


like i said above, i use my select monitor to get these readings. it shows the voltage from the signal wire of the tps and i've watched it spike as the car downshifts and drop as it upshifts - back and forth usually pretty quickly. that's the only way i was able to get this far.

i have two complete tb's now so i'll try removing and cleaning the tps on one to see what happens. replacing the tcm eliminated the neutralizing so it would seem there was some sort of deficiency there. the trans and a/t control system of this car were completely skrewd when i got it, rebuilding the trans just pointed out all the other problems - if only i had known it was going to be like this...

Edited by mountaingoatgruff, 22 December 2008 - 02:44 AM.


#10 lostinthe202

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Posted 22 December 2008 - 07:25 AM

I know nothing about the auto trans or it's controls so I won't be offended if you wait for a more knowledgeable response, but I'd say that having the bigger tires on would make no difference assuming you have the same size on all 4 wheels. You're speedo would read a tad slower then you are actually traveling but the rotations relative to each other is what matters (right?) and your vsses shouldn't care.

Good Luck!

#11 grossgary

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Posted 22 December 2008 - 07:43 AM

yep, wheel/tire size has nothing to do with this so long as they all match.

the 1mph difference is interesting. i doubt that has a difference, but do you have another subaru to hook the select monitor up to and see if it's the same? if you don't, someone you know surely does right? i'd be more than glad to see a select monitor plugged up to one of mine!

i used this same idea to save a satellite launch delay. nasa = working on cars! it felt good to come up with the idea, but i do it all the time with subarus so it was natural. "hmmm, that's weird, let me go check this other subaru...."

#12 lostinthe202

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Posted 22 December 2008 - 08:06 AM

Just another thought, is there any margin of error for those vss readings? LIke some % that they can be off? Surely they can't be expected to agree exactly...

#13 PAezb

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Posted 22 December 2008 - 08:55 AM

Just another thought, is there any margin of error for those vss readings? LIke some % that they can be off? Surely they can't be expected to agree exactly...


I'm sure there is but have no idea what it is. Having replaced the tranny mounted VSS twice now in the lifetime of the 96 OBW I can tell you that when they begin to fail it can effect shifting, symptoms of torque bind, etc.

For now, I would simple disconnect the harness from the sensor and let the default ECU/TCU (limp mode) mappings take over. It wont hurt anything, you just wont have a speedometer or odometer while disconnected, but the tach will still work. And you can find out if it will shift into third without the VSS. If it does then you can start suspecting the VSS....

#14 PAezb

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Posted 22 December 2008 - 09:05 AM

Something else I'd like to add - as cars get older, so does the wiring and electrical connections. I would suspect changes in weather temps might add to it as well. Since you indicated the tranny has had work done, disturbing the wiring harness and/or connected may have cause a open/intermittant connection. You might try checking all connections, even the TCM control fuse and reseat it in the fuse block.

Just a thought.

#15 presslab

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Posted 22 December 2008 - 10:24 AM

its 1mph at all speeds that was able to check it (i was driving in the dark looking back and forth from the dash to the monitor). i have a subaru select monitor that gives the mph and kph readings for each speed sensor, 4 readings in all. while driving the car with the monitor hooked up, i verified that vss2 matches the speedo (of course, they're essentially the same unit driven as you say by the nylon gears on the front diff). vss1 gives a consistent 1mph difference at all speeds above a few mph.


I use the select monitor software from alcyone.org.uk with my 4EAT, I modified the software with my memory addresses, of course. The one MPH difference is nothing really, the Subaru end wrench article actually says be wary if they are always the same because that means one of the VSS is not working right. Mine is usually pretty close but sometimes it is +/- 1 MPH when going straight and while turning it can be a few MPH off.

the tps is from the same jy 95 impreza the tcm came from, about 140k miles on that car. i swapped the entire throttle bodies and i cleaned the snot outta the 95 before installing it, it was quite filthy. i used brake cleaner and a rag, mostly focusing on the tb itself and i avouded getting brake cleaner in the tps. are you suggesting i remove the tps to clean it with contact cleaner? will i need to adjust it after that? i have contact cleaner already but i don't have adjustment specs for the tps so i've tried to avoid removing it. do you think that simply being dirty would cause the voltage of the signal wire to spike?


Yes remove the TPS and squirt the contact cleaner into a crack while turning it. Don't use any other solvent like brake cleaner it will damage it. I'm not sure how much it matters but I'd think the lube is a good thing too - it's probably some light silicone oil. You should readjust it, but I'm sure if you mark it's location before you remove it you'll be ok.

You ever hear a radio that is scratchy when you turn the volume knob? The TPS is the same thing as that volume knob, a potentiometer.

#16 mountaingoatgruff

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Posted 22 December 2008 - 02:30 PM

yep, wheel/tire size has nothing to do with this so long as they all match.


that's what i figured but i wanted to make sure.

#17 mountaingoatgruff

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Posted 22 December 2008 - 02:47 PM

I use the select monitor software from alcyone.org.uk with my 4EAT, I modified the software with my memory addresses, of course.


interesting site, i'll have to do some reading there.

The one MPH difference is nothing really, the Subaru end wrench article actually says be wary if they are always the same because that means one of the VSS is not working right. Mine is usually pretty close but sometimes it is +/- 1 MPH when going straight and while turning it can be a few MPH off.


this makes sense once you consider that vss1 is running off the outer hub of the transfer clutch. this hub is linked to the rear wheels and will spin in relation to rear wheel speed. vss2 is running off the speedo head, which in turn is running off the front diff so its linked to the front wheels and reports front wheel speed. the sole purpose of vss1 is to report speed differences between the front and rear wheels for the awd control system, so it would follow that there should be a difference to report.

Yes remove the TPS and squirt the contact cleaner into a crack while turning it. Don't use any other solvent like brake cleaner it will damage it. I'm not sure how much it matters but I'd think the lube is a good thing too - it's probably some light silicone oil. You should readjust it, but I'm sure if you mark it's location before you remove it you'll be ok.

You ever hear a radio that is scratchy when you turn the volume knob? The TPS is the same thing as that volume knob, a potentiometer.


now that you put it that way i'm reminded of my old fender amp. it was a nice unit louder than hell, but older than me! the volume and tone knobs were both so trashed that i had to turn the volume on my guitar all the way down to change the settings on either knob otherwise it would make scratching noise so loud i feared for the welfare of my speakers.

so yeah - i'll definitely try cleaning that tps after swinging by radio shack this afternoon.

#18 mountaingoatgruff

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Posted 23 December 2008 - 03:37 AM

so i removed the tps from the tb and cleaned it really well with lubricating contact cleaner from radio shack. i sprayed it, then rotated the internals back and forth a few times, then blew it out with compressed air at 40psi, and repeated a few times. i did notice some grime came out the first couple times. also, i tried to mark the loactions of the screws on the mounting flanges before removing so i could eyeball it while reinstalling.

i checked the voltage before test driving and it was 1.02V closed sweeping smoothly to 4.89V wot.

test drive seemed better. it didn't cycle up and down through the gears for a couple minutes but when it did it was only dropping from 4th to 3rd on occasion. i could cruise with my foot steady and it would downshift out of nowhere, but like i said it wasn't doing it that much. also, the shifts are smooth and it doesn't rev freely at all anymore - not even on modest throttle downshifts.

well, i thought maybe it was because the voltage signal of the tps was a bit high so i adjusted it to put out 0.67V closed. while test driving, though, the trans didn't want to shift at all! it would stay in 1st revving all the way to 4k (as far as i felt like going) and only upshifted after i closed the throttle all the way, didn't shift by feathering the gas.

this is pretty much why i hesitated to remove the tps, but the good news is it didn't seem to have the voltage spiking issue. there was no down-up-down-up shifting like before and the tps voltage was steady while i was watching it. i need to test drive it some more with a passenger watching the monitor to verify that the voltage spiking is cured, but it seems to be. good call, presslab!

so i tried looking around online for adjustment specs and found a nasioc post where a guy said to adjust a 99 model (not sure if that's a 3 or 4 wire type, or even if it was n/a or turbo) by unplugging the ecm then rotating the tps so that it puts out between 0.45V and 0.55V closed. my book for legacy's says to adjust a 3 wire tps so that it gives from 0.5V to 1V closed and then verify that it gives from 4.5V to 5V at wot, it makes no mention of unplugging the ecm.

hopefully my problem now is just getting my tps properly adjusted. yohy said he'd put a pdf fsm on cd in the mail for me so if i can't figure it out by then i can look it up when i gets here (thanks again, yohy!).

also, i have been running the tcm from the 95 impreza i got the tps from but my ssm started getting pissy about communicating with it through a 93 harness (kept saying error code 1, which i've learned means its not interfacing). i put the 93 tcm back in and it threw a tps code immediately where the 95 didn't. the trans acts about the same with both, i just thought it was odd that the 95 doesn't kick the code out and the 93 consistenly does. at that time the tps was at 1.8V closed. i adjusted it to be 0.8V closed and the code went away (using the 93 tcm) but it still didn't want to shift at all.

and that's where i gave up for the night...again.

#19 presslab

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Posted 23 December 2008 - 04:47 AM

i checked the voltage before test driving and it was 1.02V closed sweeping smoothly to 4.89V wot.



Looks like it's supposed to be 4.7V fully closed, not at WOT; are you measuring it like the FSM says? Looks like when using a voltmeter to take out the ECM, not sure if that means unplug ECM as well. However you have a SSM so why not use that?


[ATTACH]6027[/ATTACH]


Is it dropping out of 4th or is it just the torque converter unlocking? If the tranny temp is cold it will not shift to 4th. Maybe the temp sensor/connection is flakey. Check the SSM for the tranny temp when it shifts out of 4th.

Edited by presslab, 23 December 2008 - 04:52 AM.


#20 mountaingoatgruff

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Posted 23 December 2008 - 07:09 AM

Looks like it's supposed to be 4.7V fully closed, not at WOT; are you measuring it like the FSM says? Looks like when using a voltmeter to take out the ECM, not sure if that means unplug ECM as well. However you have a SSM so why not use that?


that's the first time i've seen that page of the fsm. i use my ssm to give a readout of the signal voltage but i'm not sure if i'm using mode f10. probably just refers to the tps voltage readout screen - i'd have to look at it again. the 93 tps gave 0.45V closed before i removed it and the 95 gave 0.9V before i messed with it.

this page kinda muddied the water for me...doesn't make sense.


Is it dropping out of 4th or is it just the torque converter unlocking? If the tranny temp is cold it will not shift to 4th. Maybe the temp sensor/connection is flakey. Check the SSM for the tranny temp when it shifts out of 4th.


the ssm shows atf temp and what gear the trans is in and its definitely downshifting from 4th to 3rd. also, it goes into 4th cold.

#21 presslab

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Posted 23 December 2008 - 10:49 AM

that's the first time i've seen that page of the fsm. i use my ssm to give a readout of the signal voltage but i'm not sure if i'm using mode f10. probably just refers to the tps voltage readout screen - i'd have to look at it again. the 93 tps gave 0.45V closed before i removed it and the 95 gave 0.9V before i messed with it.

this page kinda muddied the water for me...doesn't make sense.

the ssm shows atf temp and what gear the trans is in and its definitely downshifting from 4th to 3rd. also, it goes into 4th cold.


That page is from the PDFtown link posted in the other thread, should be for 93-96 Impreza.

My '90 Legacy TCU will not shift to 4th or lock the TC when the tranny temp is below 64 deg F.

#22 mountaingoatgruff

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Posted 23 December 2008 - 04:34 PM

i just figured out why that page makes no sense - it's for a turbo car, you can see the intercooler and such in the top pic. my impreza is an L wagon with n/a EJ18.

those pdftown links still aren't working for me, is there a page on there for n/a models?




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