Cat 3126 Throttle Position Sensor

[Paul Bowers]

Hello,

I am a new BAC member and so, new to the forum.  To be honest, one of the main reasons I decided to join was because of the information that is being shared in this venue.  A couple of tips from the forum has already saved me some time and money.  Even before I was able to get on the forum, Gerald Farris was kind enough to help me with a tire issue.

Today, I made contact with Edward Buker who lives just a few miles away from me and we talked about CAT service in the Mobile, Alabama area.  He suggested I post a problem I am having with my coach to this group and see if others have had this problem before.  

I have a CAT 3126 (330hp) in a 2001 Beaver Monterey Trinidad with 47,000 miles.  Last week, while coming back from a weekend trip, I lost all throttle control.  The event captured two different messages.  1.  91-40-1 Invalid Throttle Sign (assume Signal) (occurred  at 1674 rpm) 2.  91-45-1 Throttle Sensor CLBRT (occurred also at 1674 rpm).

I was traveling at approx 50 mph, slowed when a car pulled in front of me, after slowing I pressed on the accelerator pedal and no response.  Luckily, I was where I could safely pull over out of traffic.  Engine was idling at approx 750 rpm.  Pressing the throttle had no response, coach remained in idle.   I turned the engine off, waited a few seconds and restarted. The active faults were cleared and the coach operated normally for the next 7 miles on my way to the storage facility with normal throttle response, and no further messages.

I have thus far been unable to duplicate the problem.  Checked the throttle sensor, cable and connector under the accelerator pedal and shows no signs of chaffed wire, or connector problems.  I contacted Cat National Hotline and they had no suggestions other than take it to my local CAT dealer.  The second message captured by the computer "Throttle Sensor CLBRT" they said is not in their fault reporting manual.  I found references from two other engine manufactures of the CLBRT portion of the message and it meant  "calibration" in their manuals.  However, my sensor is a non-adjustable type.

The coach has not been driven much in the past two years, and this may be a big part of the problem.  One CAT mechanic I talked with said the 3126 likes to be driven and is not happy when it just sits.    I am now able to travel more, but want to make sure the coach is safe to do so.  I am reluctant to spend money at the CAT dealer for an intermittent problem.  My plans are to get the coach out on the interstate (locally) and drive it for a couple of hundred miles and see if I can duplicate the problem.  

I would appreciate any suggestions or comments anyone might have on this issue.

Again, thanks to all of you for your contributions to this forum, it alone is worth the price of admission.

pb

[Richard And Babs Ames]

Welcome to BAC vpbowers, we have over 110,000 on our 3126 but have never had your problem thankfully .

It could be an electrical connection problem.  Could be as simple as cleaning the connections by friction (unconnecting and reconnecting) check for corision and if present  clean with a contact cleaner (Radio Shack or other brand).

Second thought is if it is fused through a relay and the relay tripped and then reset itself or the throttle linckage made need lubrication.

I agree that frequent operation helps prevent a lot of problems. Just like us exercise is necessary to keep our parts working.

[Edward Buker]

Paul,

I did a little looking on the web as I'm sure you have. The sensors in most cases appear to be sealed potentiometers that have a wiper. Given that, they do have contact wear and oxidation can be an issue. You could unplug the unit and put an ohm meter on the non wiper leads (top and bottom of the pot) and check the total resistance. Then go across the wiper to top or bottom of the pot and as slowly as possible exercise the wiper and see if you can sense any spot with an erratic non linear result. If all looks O.K. now then I would not assume for sure that the pot was not the source of your problem, just not an obvious problem now. As a possible help if surface oxidation was the culprit, with the engine off, you could exercise the pedal full stroke 100 times or so which would help "renew" the surface contact area in case a slight oxidation issue was involved.

I also read that some sensors used pulse width modulation. Not sure that there would be any way to simply test that type unit. With an ohm meter you should quickly know if you have the pot type or not and if you can get any appropriate measurements.

The other possibilities that you run across on the web are contact issues at the sensor plug where your unplugging and plugging should renew those contacts. I doubt if that was it but you can never be sure. There is a very good product called Corrosion X that is used in marine applications around here that would be worth spraying on the plug contacts while you have them apart. It lasts and prevents oxidation and is clear and clean to use. I spray all my external wire terminals including the main electrical bay ones below the driver area. Also it is mentioned to remove the ECU plug clean the contacts, apply silicone grease, and replug the ECU plug as a possible sources of this type of problem.

It was good talking with you yesterday and knowing that you are an old audio and ham buff I know you are familiar with the old "noisy pot" issue. With audio signals you could hear the results of the pot wear.

Before I would spend the money at Cat for labor I would buy a new pot and just replace it given it is a mechanical wiper device that has to wear over time. If you do that and the problem repeats then you know for sure that is not the source of your issue when you head to Cat so they they do not waste time looking at that end of the system. I think Cat has a forum also that may be useful....good luck and let us know what you find.

Later Ed

[Tom and Pam Brown]

Freightliner in Mobile or any other Cat Dealer should be able to hook up the computer to your coach and check throttle movement.  It could also detect the fault code that should have logged into the engine computer at the time of trouble. The diagnostics on the engine are very good and should lead to the source of your issue.  If it is an intermitent problem that happens again I would replace the throttle position sensor at your first convienence. It may have to be done at a dealer to give them the opportunity to marry the new sensor to the engine computer. A call to the local Cat dealer should answer this question.

[Joel Ashley]

Paul-

Ed is right about the CAT Engine Owners Club.  Brett Wolfe there is a very well known and respected member of the American motor home community.  Joining the club has its benefits and I can recommend it.  Membership in both the CAT Club and the BAC will maximize your resources as an owner, and CAT parts and service discounts are available to members of the CAT Club, something that can easily pay back the cost of membership.  You can post a question in the CAT Club Forum or send a question directly to Brett via an email connection there, where he is wolfe102001.
http://autos.groups.yahoo.com/group/CATRVCLUB/

-Joel

[Paul Bowers]

All,

Thanks for the information.  You have all given me some great starting places to be begin troubleshooting my problem.  Also thanks for the suggestion to join the CAT RV Club.  I took the advice...joined... and actually found a similar problem posted on the their forum.  

I have been a member of FMCA since 1998 and have never joined any organization within the FMCA family.  Now in less than a week I belong to two, BAC and CAT RV.

Again, thanks to all for your help


pb