trailer anti-lock light on

[xzostd1]

I just returned from a Humvee delivery and now have the Anti-Lock light on. (at rear trailer corner)
The trailer is a 05 Doonan step.
Ideas??? I did test the brakes on ice and the anti-lock IS working.
Bill

[Larry227]

If the light stays on full time you have an active fault. 95% of the abs problems I see are related to a bad sensor or sensor extension cable but without knowing what code it's throwing it's a shot in the dark.
If you want to do some troubleshooting you can check the sensors with a multi-meter. A good sensor will read 900-3000 ohms. If you find one reading more, less or bouncing around you can then look at the cables, connections, etc and try to narrow it down before condemning the sensor. Some systems (especially Wabco) use extension cables that run from the valve down to each sensor. I've seen those cables go bad just as often as sensors. Sometimes it can be as simple as cleaning the connections or once you start looking you find sensor wires rubbed through and you just have to make a good splice.

If all else fails you may have to take it into a shop and get the codes pulled or if it really bugs you just unplug the light. Keep in mind a light that doesn't work at all is reason to fail a safety inspection. At least here it is. May be different elsewhere.

[Larry227]

Two questions I forgot to ask.

What system is it? Wabco, Haldex?

Did you happen to have a wheel seal replaced right before the light started staying on? If a hub is pulled and the sensor not re-adjusted 9 out of 10 times you'll get an air gap code afterwards.

Ok we'll make it three questions.
Does the light stay on all the time or just for a few seconds whenever you hit the brakes? I think you meant all the time but just wanted to clarify.

[xzostd1]

Thanks Larry
I'am going to pull all the rear wheels and take a look. The trailer is 5 years old with little use but.... "little use" doesn't mean things don't fail (Anti-lock light is on isn't it?!!). This will give me a chance to check the brakes, bearings and sensors. When I know what system I have I will post the info
Bill Menominee Michigan

[Larry227]

Just remember no matter what system, if you pull a hub to do a bearing or seal always tap the sensor in before installing the hub back. That way the excitor ring on the hub will push it back in to where it needs to be for proper adjustment. You don't have to tap it in a lot, just around 1/4" so.

[xzostd1]

As soon as it stops...snowing (7"yesterday) freezing rain(today) 40mph winds and 3 degrees(Wed, Thurs.)
I will get to the trailer.
Bill

[bob h]

I just returned from a Humvee delivery and now have the Anti-Lock light on. (at rear trailer corner)
The trailer is a 05 Doonan step.
Ideas??? I did test the brakes on ice and the anti-lock IS working.
Bill

Some trailer abs systems will flash codes at start-up; with the trailer connected to tractor, turn the key to the on position and wait, if the abs light starts flashing, count and record the flash sequence(s).

[GMAN]

My step deck has an ABS light that stays on all the time. The shop that checked it told me that the ECM was bad.

[Larry227]

It's not good when the ecm fails due to the expense of replacing it. I've not seen it happen a lot though, only twice in the last 8 years of working on them.

[xzostd1]

Summer arrived today! I pulled the brake drums and fired up the pressure washer. I have corrosion where the pigtail plugs into the extension cableson two sensors. I ran out of time but will inspect all the wiring back to the control unit in the next day or two. My plan is to cut out the corroded plugs and make a weather proof splice. It is a Wabco system.
Bill

[bob h]

Summer arrived today! I pulled the brake drums and fired up the pressure washer. I have corrosion where the pigtail plugs into the extension cableson two sensors. I ran out of time but will inspect all the wiring back to the control unit in the next day or two. My plan is to cut out the corroded plugs and make a weather proof splice. It is a Wabco system.
Bill

The wheel speed sensors are magnetic pulse generators which produce an A/C voltage signal to indicate relative wheel speed to the ECU (ABS computer)... I'm sure you don't care about that ; ] but, the reason I tell you is because these signals can be scrambled if the circuit is opened and then soldered back together. The ABS manufacturers DO NOT endorse this type of repair.

If you're certain that wheel speed sensor is the bad, then great, try the solder repair as you're out nothing as you will need to replace the sensor either way. But, I wouldn't suggest you cut into a GOOD sensor for this reason.

[xzostd1]

all fixed.. I cut out the two bad connectors and spliced with crimp connectors with built in shrink tube. I checked impedence of all 4 sensors at the controller (post repair) 1.2K+or- 150 ohms at each one. All the good plugs now have silicone dialectric grease installed. I had to cut almost 2 feet out of the extension wires since there was alot of migration of corrosion. The sensor side had no corrosion migration. T
Thanks for all the input
Bill

[Larry227]

Glad you got it sorted out. Although splicing that connection may not be recommended I've done it many times and haven't had one come back with a problem yet.
If you keep the male pigtail you cut off and it cleans up good it makes a great test lead for when you need to test the sensors themselves. It can be hard as heck to try and get two mutli-meter leads in that female connector to test it so the pigtail comes in handy then.

[xzostd1]

My research including input from this forum leads me to believe that almost all failures in these systems start in the connectors. I will bet that my repairs which removed 4 connectors will outlast the other 2 sensor OEM connectors. The extension wires had a additional connector and enough excess wire looped under the trailer that I could eliminate them. I also rerouted and protected the wiring in sheathing.

I trimmed the insulators on my probes so as to reach into the sockets.....using a old plug is a great idea as a test plug.
Bill