Accelerator pedal (Gen 1)

I wanted to offer an easier 'fix' to the accelerator problem. I had been rebuilding accelerators after Doug went to China but there was a recent NASA GSFC report on 'tin whiskers.' Since I still had some of the old inventory, not yet rebuilt, I tested a couple and it appears to work.

The NASA 'tin whisker' report indicates a typical VOM does not have enough voltage and current to 'burn out' a tin whisker. You can see the non-linear effects but the VOM won't clear the problem. So using a 12V 'wall wart', I walked the pins while cycling the encoder to 'burn out' any tin whiskers of three known, bad encoders. After the pin walk with an encoder cycle, they appeared to be OK and a second walk-the-pins did not show any changes.

The beauty of this approach is you don't have to crack-open the case. Just walk the pins with a 12-24 V power supply and cycle the encoder to vaporize any bridging whiskers. It certainly is a lot less work and cheap.

Will the whiskers grow back, probably. No one has figured out a permanent solution short of special coatings or different materials. If another whisker is growing but not reached another contact, it may be days, weeks, months or years before the symptom returns. But this provides an alternative to the more invasive fix.

GOOD LUCK!
Bob Wilson

 

Assuming it's possible, wouldn't it be preferable in the long run to replace the unit with the non-contact Hall-effect design that Toyota implemented in the mid-year 2002's?

 

As everybody knows, our 2003, NHW11, has the same accelerator assembly as the 2001. The Hall-effect accelerators did not show up until the NHW20.

I had done some experiments in the area but didn't see the volume nor value-added of going further. Then there is a risk that someone using it might claim it caused an accident. It just didn't make sense.

Bob Wilson

 

Here is a quote from northwichita:

"In mid-2002 Toyota changed to a Hall effect sensor unit that was much more reliable."

Read more: http://priuschat.com/threads/mild-case-of-big-hand-syndrome.108684/#ixzz1wfZ9IJSA

Is this not correct?

 

Hey, are you really the "new" bwilson4web? If so, something happen w/your old id?

 

We have a 2003 Prius and the manuals. The accelerator assembly is identical to those in the 2001-02 year versions.

I suspect Toyota engineering decided to go with Hall effect sensors in 2002 but it would not instantly go into all models. In fact, I bought a Scion accelerator assembly, post 2003, that still had the pot encoder. I bought it to see if we could use Scion encoders as an alternative.

A lot of times engineering will figure out a new way of doing something but that doesn't mean the existing models in manufacturing will be getting the new technology. It usually has to wait until a new design comes out to incorporate all of the engineering advances.

Bob Wilson

 

Yes, everybody knows I'm Bob Wilson. <grins>

The password-recovery system has a problem with sending the e-mail to change/fix/replace a forgotten password. But I had this 'joke' account from several years ago and ... it worked! <grins>

I didn't reuse my old avitare since I expect Danny will fix the e-mail eventually. Then I should be able to password-recover and go back to being ordinary 'bwilson4web.'

Bob Wilson

 

Hi Bob very interesting about blowing up tin whiskers. I wonder if steering angle torque sensors could be revived in the same fashion. Physical inaccessibility is the bigger problem for them.

We are all 'new members' now - I feel all born againy.

 

Bob,

Are you still doing the rebuilt APA thing?

My issue just started. I have an '01 with about 175K on it. Occasionally as I'm criusing along at 35-45 the ICE cuts out and it slows suddenly. The MFD shows 100mpg and there are no warning lights. It doesn't last long and reverts back to normal at the next stop. Does this sound like Big Hand Syndrome or something your swithch would fix? Thanks!​

Read more: http://priuschat.com/members/bwilson4web.10647/#ixzz1xD7zpGfh

 

I stopped rebuilding after my bank decided to 'fee' my account out of existence. I would have had to leave a substantial amount of cash in the account not drawing interest so it didn't make sense to continue. Without a bank account, a company pretty well ceases to exist and there was not enough volume to justify keeping it going. Later, I read about the 'tin whiskers' and after testing with the existing inventory, it is what I recommend now.

There are many things that can cause "the ICE cuts out and it slows suddenly." I advocate getting a scanner that can read the Prius codes like a ScanGauge II and first checking to see what the car is reporting. Getting metrics for an accurate diagnosis is always a good first step with our Prius.

Bob Wilson

 

So codes will show up on the scanner even if there are no warning lights on?

 

Yes but there is more. Programming in the XGAUGEs for the accelerator, you can actually see the same data the hybrid vehicle (HV) computer sees. This is a lot easier than pulling the accelerator out; mounting on a test fixture and; using a VOM to measure linearity.

Bob Wilson

 

Hi Mike,

I was hard to see your note because it was embedded in the quoted text but here is what I see:

• "wall wart" is a regular plug-in power supply, typically a DC but an AC model works too.
• "walk the pins" means putting the leads against all possible pairs of pins. There are 6 pins so there are 5+4+3+2+1 combinations, 15 combinations. Actually there are on four combinations that really work but it is a little challenging to describe how to find the 'sweep' and 'end' pins. The others do no harm.
• "cycling the encoder" means pushing the accelerator down and back, cycling the range. This sweeps the pot to try and burn out all of the whiskers.
• We are trying to 'fry', actually vaporize the tin whiskers. The internal parts are quite robust at 12 V or less.

Bob Wilson

 

Hi there.

I tried to fix my accelerator pedal sensor (potentiometer).
No success so far.
I disassembled the potentiometer house.
I used a hot air soldering station to bend plastic fixing, so i could remove the ceramic plate without cracking the housing.
After that I could bend back plastic to hold the plate.

At first time I used contact spray to clean the surface of slider paths.
I tested the results with a PC speaker and 1kOhm resistor connected in series with the potentiometer. I used a 12V DC supply.
I heard the schratching sound as I moved the potentiometer.
The sound were not much less after the treatment.
No difference in driving...

At second time disassembly I realized that the inner slider's surface is very coarse -as you can see on the photo.

I tried to polish the surface with a polish sheet.
The surface became smoother but on the edges bare metal showed up under the black coating, so I ended up with polising.
The noisy sound was reduced to 1/3.

I put back things to work and I realized smoother operation and about half times of occurence of "big hand" syndrome.
So I'm not satisfied with the results.
I will order a new potentiometer from ebay. It's about 33$. I will tell about results...

 

Hello ger-ev. I had 100% success rate cleaning those potentiometer traces, but yours seems to have been further degraded. Perhaps Bob Wilson will have a comment?

Interesting that you can buy the part on ebay.

 

I've received the sensor.

They claimed that it is a new unused item, but i got a used one. The outside wear was higher than mine.
I sent a message to the seller with photos. They apologized and I've got a full refund.
Anyway the potentiometer noise was at the level of mine after the treatment.
So I decided to replace the ceramic pate. I did polishing on the "new" one and applied silicon oil on slider surface.
I don't know if it is a good idea, but I realized slightliy less noise with silicone oil. the time will tell..
So now I use the car with this and I haven't experienced big hand effect until now.

I found the part on ebay with "prius accelerator pedal sensor" search.
There are many results with this price.

You can test the surface with a peace of wire sliding on the tracks, before reassembling the housing.
The outer track's unused area was completely "silent". I cannot reach that quality with polishing but can make better.
end.