TPS Resistance

Stevebsy · #1 03-18-2001, 04:01 PM

Is there is a misprint in the Shop manuals, or is my TPS way off.

Between pins 1-3 is should be 5k and it is 4.59k ohm (fine)

But it says between 2&3 it should be:
10k-12k at close
5k at open

I am getting .15k (ie 150 ohm) at close and 4.66k at open

The book also says: "Ensure resistance increases while the throttle is opening" which is contradictory to the 10k at close and 5k at open. Which is right?

Section 2-7 page 78 is where I'm looking

Thanks

Aredubjay · #2 03-18-2001, 09:17 PM

From what I understand, accurate TPS resistance is difficult to read with a select monitor, much less a multimeter. The 10-12K sounds right, at least, that's what the tranny folks who've been holding my car hostage since last Monday told me. They also told me that it was only putting out half the resistance. God only knows. I'll have my new TPS by Thursday and have it installed to see if it cures my 2-3 flair. I can't tell you more beyond that, sorry. Anyone else?

1994SubaruSVX · #3 03-23-2001, 12:02 PM

what the hell is the TPS?? jesus i feel like i am always learning when it comes to this car!!

Aredubjay · #4 03-23-2001, 12:10 PM

The TPS is the "Throttle Position Sensor." It senses the position of the throttle to help the ECU learn your "driving habits" and control various other functions in the ECU. It also (something I've learned, since I'm waiting for one to be shipped), sends signals to the TCU to control line pressure to 2-3 shift solenoid. When the tranny shop called and said that they'd diagnosed a faulty TPS as causing my 2-3 shift flare, I thought WTH? Then, I cracked open my manual, and sho' nuff, there it was in black and white. Of course, this is the same manual that, in the trouble diagram, tells you that if you check the Throttle Position Sensor and it does not check out Okay, then, you're to "Replace the Throttle Body." (Do you think they meant, the Throttle Position Sensor? -- I've found several typo's)

#5 03-27-2001, 11:43 AM

Randy - I'd be really interested to know whether your new TPS fixes your 2nd/3rd shift 'flare'. My SVX has been doing this since I've had it (about 10,000 miles ago). Happens only on very light throttle conditions and actually seems to pick up 1st gear momentarily and then slips into third. The diagnostic shows an error code which indicates the TPS, but I've never gotten around to fixing it. If it fixes yours - I'll get one too!

#6 03-27-2001, 12:23 PM

This all begs a few questions.

First, does cleaning the TPS solve the problem?

Second, is the TPS on the SVX identical to TPS's on other Subarus much like the MAF sensor is? (possible cost savings-Impreza MAF same as SVX, much cheaper)

Third, mine slips between 1st and 2nd WTH causes that?

John

Aredubjay · #7 03-27-2001, 02:15 PM

Well, I should know today. After being without my car for 14 Long and gut wrenching days, the TPS came in. They are installing it as we speak. I expect the call telling me the car is ready any moment now. Wish me luck.

#8 04-01-2001, 10:23 AM

A DIRTY TPS:

In my Buick, wired to a scan tool, I had crazy injector pulse widths and ignition advance. Presumably it's the same in the SVX, though in my case I experienced very odd shifting. Cruising at 80 or so, I could take my foot from the gas and as the car decelerated below 60 it would hunt for a gear. This was a consistently repeatable problem, and I thought the tranny was dying. It also shifted when it shouldn't have on acceleration. Finally, I saw a Code 31 (TPS). I cleaned the TPS (the hard way, the first time) and the problem has been gone for many months. Cleaning is very simple:

First, understand that the TPS is a variable resistor, schematically identical to the volume control on a simple radio. There's an arc-shaped fixed-value resistor connecting the HIGH and LOW terminals. The system sets a specific voltage across those two points, and that voltage does not change.

In a volume control or TPS, there is a wiper that moves along that resistor, following the arc as the "knob" is turned. When the wiper is all the way in one direction or the other it reads either ground (zero) or max (the applied voltage). Leading from the wiper is the selected signal, or voltage, depending on its position along the fixed-value resistor. There is a variable voltage appearing between the wiper and the other terminals, depending on the wiper's position.

If the fixed-value resistor surface, or that of the wiper, gets dirty, then the wiper won't make proper contact along its path, sending erroneous signals to the system. It's like moving a volume control and hearing static.

In cars, the wiper is connected to a shaft that is connected to the throttle in such a way that as throttle position varies, the resistance (and therefore the voltage) varies with it, and that signal is used to determine driver intentions (throttle position). In most cars, the TPS is a sealed unit. In the SVX it is not sealed, and there are two ways to clean it.

In any case, the first thing to do is carefully scribe one or more marks so the unit can be replaced precisely where it was. Then remove the connector, push a hose out of the way, remove the screws (don't lose them!), and pull the TPS off of the shaft that drives it.

THE HARD WAY:
Push the spring tab out of the way and disassemble the unit. DON'T LOSE THE WASHER that maintains pressure between the wiper and the fixed resistor. Clean the entire assembly by flooding with contact cleaner, rotating, repeating, air drying, etc. etc. Reassemble - but be very careful because it's a pain in the neck to get the spring right without breaking any of the plastic components. Then pridefully examine the unit, spot the hole in the connector socket, and slap your forehead.

SIMPLE CLEANING:
In the connector socket you'll see a very small hole adjacent to one of the pins. Using a commercial contact cleaner (Radio Shack is ok), flood the unit. Rotate the shaft several times. Let the fluid drain around the shaft. Repeat. Then, blow air through the unit till it's dry, rotating the shaft repeatedly.

You can try to measure the resistance of the system as the wiper is rotated, but don't expect definitive results because any points of ambiguity (static producers, in a radio) will be extremely small, and you may go right past them too rapidly to see anything on the meter.

#9 04-10-2001, 08:55 AM

Aredub - I'm 'itching' to know whether a new TPS fixed your 2nd/3rd 'flare' problem! Assuming you've got your SVX back on the road, that is.

eddycat2000 · #10 04-10-2001, 09:16 AM

Quote:

Originally posted by m30svx
Aredub - I'm 'itching' to know whether a new TPS fixed your 2nd/3rd 'flare' problem! Assuming you've got your SVX back on the road, that is.

Ooooh...Oooohhh!!! Raised hand shaking violently

I can answer that one! He got the TPS to them and they told him after installing it that they must have burned up the forward clutch while testing the TPS. So they had to remove and re-rebuild the tranny. (Which is exactly wht I told him was going to happen). I think they didn't charge him any labor, which is good, he might have killed someone at that point. But he's still out the cost of a perfectly good TPS.

I'm curious Aredub...did they give you your old TPS back, and if so, are you going to reinstall it and see how the thing shifts? And if it shifts okay, are you going to start doing some tater slapping? And if so, could you have some of yer advertising type friends tape it for us?

svxter · #11 04-10-2001, 10:30 AM

Quote:

Originally posted by eddycat2000

I'm curious Aredub...did they give you your old TPS back, and if so, are you going to reinstall it and see how the thing shifts? And if it shifts okay, are you going to start doing some tater slapping? And if so, could you have some of yer advertising type friends tape it for us?

Somehow, I get the feeling that he's going to be very unlikely to even touch the TPS at this point.

Aredubjay · #12 04-10-2001, 11:57 AM

I didn't even ask for the old TPS back (my bad!). I had millions of things to do before taking off for PA, so, I just asked what the charges were and when told N/C, I gladly went on my way. They told me if I had any questions, after driving it, to give them a call. I just figured after 24 days they wouldn't have the TPS anyhoo. Oh well. I've got my car back, it runs like a scalded ape, the shifts are (just for you, eddy) "Velvet" smooth.

One thing I have noticed: prior to the TPS change, I had a "fluctuating idle." It would kinda "pulse" at idle, not really enough to be annoying, but enough to barely be seen on the tach. That is gone now.

Gosh, I knew I missed this car, I just didn't know how much. And, eddy, I'm not so smug as to not be able to accept an "I told you so" every once in a while.

So, we'll consider it said.

As for whether or not the TPS cured the problem -- that's still a "mystery." Sorry, guys.

#13 04-11-2001, 04:14 AM

Eddycat - are you saying that it is your opinion that the forward clutch was more likely to be the cause of the 2nd/3rd shift 'flare' rather than the TPS?
Also is there any evidence that cleaning the TPS actually makes a difference?
Apart from that I'm glad that Randy has his beloved SVX back together !

eddycat2000 · #14 04-11-2001, 09:08 AM

Quote:

Originally posted by m30svx
Eddycat - are you saying that it is your opinion that the forward clutch was more likely to be the cause of the 2nd/3rd shift 'flare' rather than the TPS?
Also is there any evidence that cleaning the TPS actually makes a difference?
Apart from that I'm glad that Randy has his beloved SVX back together !

I can only tell you what I told Aredub. In all the years that Subaru used TPS's I have *never* replaced one. However, I used to either rebuild or replace at least one trans a month, sometimes one a week. Heck, I don't even recall having a tps code come up on the select monitor.

As for cleaning the tps, I can't say, I've never done it, nor do I know anyone personally that has done it.

I'm glad he got his car back also. It's a darn shame that he had to go through such an ordeal to get it back though.