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  1. #1
    Bobtail Member
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    Beer 1 Utility trailer ABS light on

    I have an Utility trailer with ABS and every time I brake the ABS light that is located almost all the way rear turns on. I am pulling it a with a tractor that has ABS. Please help


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    Sounds like your wiring is messed up and your ABS is tied into your Brake circuit. The ABS light should come on for a minute or so when you turn the key on and then go off. If it stays on your ABS isn't working. Pull on the johnson bar and see if the light stays on as long as the brake lights do.

  3. #3
    Light Load Member AgLaw's Avatar
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    Your trailer ABS system IS correctly (and supposed to be) tied into your brake light circuit. That is designed as a backup to the constant powered "center pole" conductor (blue wire) should you have a failure. However, most older tractors never had constant power to the blue wire as it was used for auxiliary purposes (like dump valve activation on spread axle trailers). Thus, with older tractors and newer trailers, the trailer ABS is powered solely by the brake circuit; and, upon each service brake application, the trailer ABS module will go through a "self check" where the ABS light comes on momentarily.

    First things first, does the ABS light come on and then go off within 1 or 2 seconds of applying and maintaining an application of the service brakes while the vehicle is in motion? If the light goes off, the trailer ABS is operating normally in that regard. If the trailer ABS light comes on and stays on for the duration of the brake application, you have a problem with the trailer ABS system.

    Whatever the case, you need to find out if your tractor was originally (or currently is supposed to be) equipped with constant power to the blue wire, center pin conductor. If the tractor is equipped with constant power, you need to find out why that circuit has failed. It could simply be a blown fuse or circuit breaker (in which case you need to find out why the circuit failed), or it could just be a bad connection in the plugs. A test light will be the only tool you really need to find out.

    Please note that not all tractors that have tractor ABS were equipped with constant power to the blue wire circuit of the trailer plug. Some builds from '94 to '96 had it and some didn't as standards hadn't been developed nor implemented. None of my '96 models were equipped with ABS nor constant power. However, I have retrofitted most all my older units to have constant power on the center conductor--it can be done at minimal cost.

    So I can be of more assistance, what years were the truck and trailer manufactured (and this isn't necessarily the model year of the vehicles!)?

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  5. #4
    Light Load Member Stevens Sucker's Avatar
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    I Have pulled trailers where it stayed on all the time and some that it never came on, I always use the trolley brake to check that they work and I am coupled, but I guess according to the above post the ABS may or may not have been working. I called the shop once and was told the light should be on all the time the truck is running, but what do I know. Thats what whomever answered the phone told me. Just my 2 cents.

  6. #5
    Road Train Member Les2's Avatar
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    The light isn't supposed to be on unless there is something wrong.

    But if you don't have a hot wire run to your ABS it will come on and should go back off, if you keep holding the brake. If it flashes that usually means there is a problem.

    This is on an 07 MAC so older models may be different.

  7. #6
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    ABS problems...

    I have read all the cooresponding answers to Duliz's concern. First, allow me to introduce myself. I work at a Marine terminal here in Portsmouth, VA. I manage a chassis pool for all the shiplines around the world. My highest priority is to maintain a sufficient budget expenditure that is focused on M&R. In reference to cost basis, our highest financial expenditures are TIRES AND ABS VALVES. Let me repeat myself..TIRES AND ABS VALVES!! Hence, we have focused a lot of our attention to these problems. I can safely say that I know quite a bit about both items extensively.

    The ECU on the ABS is a sensitive and delicate item that is usually attached to the Service Valve on the Air Tanks. The Yellow ABS light at the rear of the chassis is NEVER, EVER suppose to stay on during corrective operating conditions. There has been a few reported concerns about the ABS light illuminating during an applied braking application while the trailer is in motion. I believe that has been narrowed down to improper wheel sensor positioning, loose terminal connections and ground failures. At any rate, if the light does illuminate at any point in your travels, there is either a stored fault or an active fault that your ECU has noticed and captured. It is not safe to ignore and should be diagnosed. In addition, USDOT will have the option of detaining your equipment for unsafe operations. I will check back with these posts as often as I can to help clear up any misunderstandings and specifaction resolutions. I'm not getting paid to diagnose your problems, so just bare with me on any of my posts. Good Luck, safe travels and don't let anyone rip you off!!
    Last edited by Guidoaviano; 02.17.2009 at 02.32 PM.

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  9. #7
    Road Train Member Heavyd's Avatar
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    If the trailer is older than 2000 the ABS ECU will only get power through the brake light circuit. The light will come on when you are braking and then go out. There are several different manufactures of ABS systems and they all have different ways of showing operation/faults lights. Basically, if the light never comes on, there is a problem, if the light never goes out, there is a problem. On the older trailers with power to the ECU through the brake circuit usually the ABS light comes on when you make a brake application and then goes out after a couple of seconds. If this happens it is just a status light showing the ABS is ok. If you hit the brakes and the light comes on and stays on, or starts to blink, there is problem. If you hit the brake and the light never comes on, there is a problem. Any trailer manufactured after 2000 has to have the ABS constantly powered by the center or blue trailer cord circuit, (if the truck is new enough to have this too). This type usually when you plug the trailer in or turn the key on the ABS light will come on and go out to show it is ok. If it doesn't come on or stays on, there is a problem. Most trailers will have some kind of ID sticker showing the brand of ABS system on the trailer and sometimes have the light condition instructions. If you are not sure, get the VIN from the trailer and call the manufacturer for the proper info. Hope this helps.

  10. #8
    Light Load Member AgLaw's Avatar
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    Quote Originally Posted by Guidoaviano View Post
    I have read all the cooresponding answers to Duliz's concern. First, allow me to introduce myself. I work at a Marine terminal here in Portsmouth, VA. I manage a chassis pool for all the shiplines around the world. My highest priority is to maintain a sufficient budget expenditure that is focused on M&R. In reference to cost basis, our highest financial expenditures are TIRES AND ABS VALVES. Let me repeat myself..TIRES AND ABS VALVES!! Hence, we have focused a lot of our attention to these problems. I can safely say that I know quite a bit about both items extensively.

    The ECU on the ABS is a sensitive and delicate item that is usually attached to the Service Valve on the Air Tanks. The Yellow ABS light at the rear of the chassis is NEVER, EVER suppose to stay on during corrective operating conditions. There has been a few reported concerns about the ABS light illuminating during an applied braking application while the trailer is in motion. I believe that has been narrowed down to improper wheel sensor positioning, loose terminal connections and ground failures. At any rate, if the light does illuminate at any point in your travels, there is either a stored fault or an active fault that your ECU has noticed and captured. It is not safe to ignore and should be diagnosed. In addition, USDOT will have the option of detaining your equipment for unsafe operations. I will check back with these posts as often as I can to help clear up any misunderstandings and specifaction resolutions. I'm not getting paid to diagnose your problems, so just bare with me on any of my posts. Good Luck, safe travels and don't let anyone rip you off!!

    I've been pondering exactly how I should respond as your post seems directed my way. Rather than enter a lengthy debate with me having to quash several fallacies, I'll extend a warm (but not fuzzy) welcome to the forum.

    However, I do stand behind my previous post; and for anyone that disagrees, I would advise you to review the available troubleshooting/repair manuals. Most are freely offered on the net. You may save yourself a headache (or two) and you company some money.

    Again, welcome. I look forward to hearing more from you. And since we're on the subject, perhaps you could inform us as to which manufacturer's products have been the most reliable and/or the most unreliable in your operations. I personally only run Meritor WABCO's trailer ABS units. They've been fairly reliable with only two failures in over ten years. One of those was not the fault of the ABS unit, but that of incorrect wiring terminations for the forklift we carry at the rear.

  11. #9
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    ABS/ECU Manufacturers

    Quote Originally Posted by AgLaw View Post
    I've been pondering exactly how I should respond as your post seems directed my way. Rather than enter a lengthy debate with me having to quash several fallacies, I'll extend a warm (but not fuzzy) welcome to the forum.

    However, I do stand behind my previous post; and for anyone that disagrees, I would advise you to review the available troubleshooting/repair manuals. Most are freely offered on the net. You may save yourself a headache (or two) and you company some money.

    Again, welcome. I look forward to hearing more from you. And since we're on the subject, perhaps you could inform us as to which manufacturer's products have been the most reliable and/or the most unreliable in your operations. I personally only run Meritor WABCO's trailer ABS units. They've been fairly reliable with only two failures in over ten years. One of those was not the fault of the ABS unit, but that of incorrect wiring terminations for the forklift we carry at the rear.
    Allow me to appologize if anything i said seemed personal or directed at any post. I think my post was extremely too vague and short. To capture the true essence of toubleshooting would take extensive training and to append that information on paper would be encumbersome. At any rate, I was just trying to simplify an answer for the one driver having random problems.

    As far as analyzing the longevity of ABS/ECU valves, that will require a few independant variables. First, I'll generalize the concenus.

    We operate a fleet of 17,000 chassis. Approx. 96% of those chassis meet the FHWA criteria for the ABS law. Hence, approx. a little over 16,000 chassis have ABS/ECU's mounted. In the last five years, we've replaced approx. 1,300 ABS/ECU valves. Our primary ECU manufacturer is Meritor WABCO. Our second popular ECU manufacturer is Haldex and the fewest amount of ABS/ECU's we use is from Bendix. If I had to take a stab in the dark, I would say that over 70% of our fleet is Meritor WABCO. Haldex consists of close to 20% of our fleet. Now approx. 99% of our Meritor WABCO's are Easy Stops 2S/1M Basics for the simple reason we only provide our front axle with wheels sensors. It serves the purpose of safety and also minimizes the potential problems that can occur within the ECU. LOL, to FINALLY and PARTIALLY answer your question, almost ALL (88%) of the Meritor Wabcos fully operate effectively for at least 6 Years. Even though six years may not seem like a long time, it truely is!! I think that we may have had ONE possibly ONLY 2 of their ECUs malfunction before their warranty expires. In this industry, that's pretty #### good! In reference to the Bendix, they are more expensive and less reliable. I'm not going to be a reliable source of information for any statistical analysis with the Haldex. But I will say this, we do everything we can to stay away from them. I think there's a manufacturer defect with the casing and the silicone they put over their circuit boards. I'm not sure what the problem. So, if you want my opinion, go with the Meritor Wabco and spend the extra few dollars for the software troubleshooter. I personally have troubleshooted so many, that I know most of the shortcuts to take. Sorry for this lengthy and probably disgraceful grammer. Don't have time to proofread or elaborate on anything right now. Have a great day. -Bill

  12. #10
    Light Load Member AgLaw's Avatar
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    Bill, thanks for the info. Sounds like you've got a full day's work for sure. However, I'm a bit surprised by the Bendix revelation--the lack of reliability is contrary to what I've been told previously. As I mentioned, I only have Meritor's Easy Stop and Enhanced Easy Stop on my trailers. The revelation is interesting because it seems that Bendix is taking over the tractor market share from Meritor these days, but Meritor seems to be maintaining it's trailer market share.

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