A Question for the Electrical Experts - ABS Code 68 - L4 switch signal

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Joined
Oct 28, 2011
Threads
24
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331
Location
Dallas TX
I recently acquired a 2000 LC with 167k miles. Runs well and in good shape. Seller is a member here and a crook (stevenp). That is a story for another day. But when I purchased the truck and drove it, all was well. When I got it home (100 miles) I discovered issues.

I first noticed that the truck was not going into overdrive. Button and light worked, but no overdrive. First thought was transmission. But when I investigated further, I noticed that the crook removed the dash lights for Trac, Trac off, and ABS. I pulled the codes and found several Trac and ABS codes. I cleared them, did a few system resets, replaced all the dash bulbs (just the fact that some were missing caused error codes).

I am left with a code 68 which is the signal for the L4 selection. I went through the tests described on the FSM and it passed those tests. I decided to go back to basics and did a test of the battery and alternator. Battery is fine, relatively new. Regulator failed, alternator was fine. I replaced the alternator with a reman Denso unit purchased on Amazon. Install went smoothly. Have not had it re-tested. My theory was that a bad regulator could have been triggering the 68 error.

Once cleared the 68 error will come on randomly. Sometimes I can drive 20+ miles before it comes on, other times it comes on immediately. The dash warning lights always reset themselves when shut down and restarted.

As to the OD problem. In the process of reseting all of the ABS and TRAC codes, that problem was fixed. The transmission shifted normally. However, when the ABS/Trac lights were on, the shift points were later.

Current Issue:

I decided to depart for my 3,000 mile trip from TX to Colorado with a lot of off-roading. Idiot lights were the only problem that I was experiencing and the OD was working normally. 28 miles from home and from resetting all of the codes, the ABS/Trac lights came on - no surprise. Then a couple of miles later, the OD stopped working. Hmm, there is a connection here. I turned around and parked it. Took another car to Colorado.

Here is what I think is happening: There is an issue with the Trac/abs computer, L4 switch, and/or wires to and from those units. It causes the transmission to think it is in L4 causing the later shifts, and the inoperability of the OD. If I am not mistaken, OD is not available if you are in L4.

While on vacation, I am trying to determine my next steps. Any recommendations? Seen this before? Sympathy? I will update this thread as time goes by. But I won't be home with the truck for a couple of weeks.
 
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Sorry to read about these troubles. It might be worth pulling the toyota service history via VIN to see what, if any, dealer diagnostics and recommended repairs were declined by the PO. Just a thought.


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Thanks for the suggestion Paddo. Forgot to mention that I did that prior to purchase. Only record listed was about the dash lights. Recommendation was to replace abs computer for $2k. That was over a year ago and I don't have much confidence in that diagnosis as many here state that it is a typical dealer solution to all problems. However, if it is the solution, I don't mind paying for it.

I asked the seller about that issue and he said that he never had any issues with it. That is where the lying started and I didn't realize that he discarded all of the error light bulbs.
 
The truck loaded and ready for Colorado. It didn't make it!

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You may be on the right track with your thinking about the transmission thinking the truck is in L4. I would suspect the wires/connectors before I suspected the abs computer, because the wires/connectors are more vulnerable to corrosion/rodents/etc. It will be a challenge to find a bad wire or connector, but a visual inspection of everything leading to the abs computer may be a good place to start. I assume you did a MUD search for the issue.
 
Thanks sandroad. Yes I have searched the internet long and hard to no avail. I will thoroughly go through the connectors and wiring when I return.

That abs computer is pricey at $1500!

All is not lost. We are enjoying our 4wd adventures in my wife's Mercedes G500. It is more than capable off road! I am just not as willing to tear it up!
 
I'm surprised that no one has experienced this issue before! Help!
 
Quick update. It has been about 4 weeks since I posted this up. During that time, the car sat in my garage for a couple of weeks - in a dry environment. I have been driving it off and on for a couple of weeks - even for longer distances and absolutely no lights or issues.

My theory is now that moisture was involved in causing a short. During the long time of sitting, everything has dried out and returned to normal.

Yesterday I inspected and cleaned all of the connectors, relays, and control units behind the glove box. There was no indication of water or moisture. To be safe, I blew out the sunroof drains too. They were clear. I also went under the truck and unplugged, cleaned and inspected all of the connectors going into the transmission. No visual issues there either.

Again, with the concern of water being the issue - I was fortunate with getting a rainstorm in Dallas yesterday. I drove about 30 miles in the rain aiming for big puddles, etc and didn't have any issues. I even tested the L4 gear with center lock on/off. Everything worked well.

So while I am not necessarily calling it "fixed", I not going to look for more problems unless the lights come on again. My thought continues to be that something got wet, shorted, and now has dried out. Hopefully, it won't get wet again or I have managed to clean a dirty connector.

All is well and the truck is driving perfectly! Thanks for reading.
 
You had said possibly moisture being involved. Is it possible this was a flooded car from the hurricane Katrina days? Sorry this is not a recommendation but it is sympathy.
 
Dawg,

Katrina was a loooong time ago. And this thing would be rusted out by now if it had been flooded back then! Truck hasn't lived in hurricane zones during its life.

No indication of water under the dash, carpets nor anywhere on the car. So I don't think water entered the truck. But there could be a connector with a bad seal or wires (on the exterior) that have become brittle or something.

Drove it a lot today in the rain without issue. I will continue to monitor it.
 
I posted in another thread then found this one, I am having the same exact problems as you had. My overdrive issue didn't start for a couple weeks after the lights started coming on but what is described above is what I am experiencing to a T. I have been digging and can't find any corrosion. Any help on where to look would be appreciated...
 

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