My truck is currently throwing an ABS warning light on the dash. Through some preliminary leg work online I've found this can be caused by either a faulty ABS control module or a bad ABS sensor. The ABS module is expensive, but the sensors are relatively cheap. What I haven't been able to find is a good approach to diagnosing where the problem actually lies, and due to cost, I'd prefer not to simply replace everything hoping to solve the problem.

So SigForum automotive knowledge base, how do I diagnose what specifically has failed and needs to be replaced?

What kind of vehicle are you working on first thing?

Scan the system for trouble codes and start there. Just hanging parts is going to get real expensive real quick.

It can be as simple as rust on the reluctor wheel or a broken wire on a sensor to a corroded connector or as expensive as an ABS module. Even if you pay for someone to scan it (a lot of D-I-Y stores will scan it for free at least to generally get you where to look) it could be worth it.

Also, either get a manual on your vehicle or see if your local library has All Data available for your use. A general manual like a Chiltons or a Haynes might get you into more trouble than necessary. Get the one that the professionals use.

Just as shovelhead said, we need more information. Year, make, model and engine first. The code or codes will go a long way with diagnosing the issue.

"Control module or sensor" is swinging a wide loop. Do you have any idea what code or codes you have? Do you have any kind of scan tool or code reader that can read ABS? An OBD-II reader only works for the engine light. If not, here is a sampling: https://www.amazon.com/s?k=abs...8&ref=nb_sb_ss_i_1_8 Actual module failures are uncommon, but at this point nothing is off the table.

Defective wheel bearings can trigger the warning too.

What kind of truck and year?

Have you had the codes read? If it's a sensor it may tell you which wheel is the problem.

I agree it's likely not the module but no way of knowing with the info you have.

quote:

Originally posted by shovelhead:
What kind of vehicle are you working on first thing?

Sorry guys, its late and I was tired when I posted the thread.

Vehicle Information... 2001 Ford F150 SuoerCrew / 2x4 / 5.4L V8 / Automatic Transmission

I have a Haynes manual, somewhere, but haven't been able to lay my hands on it yet. Will look some more tomorrow.

My cheap code reader won't read ABS codes, so I'll try and get by the local AutoZone or NAPA tomorrow and see if they can provide some scan results.

quote:

Originally posted by Sunset_Va:
Defective wheel bearings can trigger the warning too.

I did a full brake job on the truck less than 10k miles ago and replaced all the front wheel bearings (required with the rotors/hubs) as part of the process, so I doubt its a wheel bearing issue.

1. Check sensor wheel area for debris, grease, etc. that prevent the sensor from seeing a rotating wheel.
2. Check wires from sensor for cracks and fractures. If ABS dash warning comes on when you are turning wheel hard to one side, then stays on, you may have a cracked sensor wire. These can be fixed.

You have a Haynes manual "somewhere?" Those are barely adequate for simple repairs and won't cut it for things like this. Mitchell and AllData have professional-grade shop manuals (because they are the factory shop manuals) available as an online subscription for an individual vehicle. They don't cost that much, either. I have used both in professional capacity and they have their pros and cons. Mitchell has better wiring diagrams, with the component locations already on the diagram so you don't have to look on a separate page for them. AllData is a little easier to navigate to the page you want and does a little better if you work with, for example, interior trim like door panels. Mitchell manuals AllData

My 2003 Silverado started turning on its antilock brake warning light a few years ago. Tried scraping the rust off all the electrical grounds to no avail and finally came to the conclusion the ABS module needed replacement. Wasn’t worth spending the money so just drove it without a working ABS. Figured that’s no different than how I drove my vehicles for the first 20+ years prior to ABS coming into widespread use. The old “pump the brakes when necessary” routine.

Like egregore said, you need to have the code read and then go from there.

Edit: Went back and read your last post. You may have slightly damaged one of the wheel sensors when you replaced your wheel bearings. You wouldn’t be the first to have done that.

Again, check with your local library for AllData in online reference sources.

Even if they are closed in some cases many libraries are allowing them to be accessed with your library card remotely, or maybe if you have a friend in a shop they can print off those diagnostic pages for you.

Haynes was good in it's day, before all the electronics entered into play.

quote:

Originally posted by bigdeal:

quote:

Originally posted by Sunset_Va:
Defective wheel bearings can trigger the warning too.

I did a full brake job on the truck less than 10k miles ago and replaced all the front wheel bearings (required with the rotors/hubs) as part of the process, so I doubt its a wheel bearing issue.

Hold the boat here. Not familiar with Ford trucks but if the ABS sensor is an integral part of that rotor and hub assembly that could be the problem.

Chinese wheel bearings, especially the lower price point ones at least in my opinion are junk. I worked in a dealership parts department and a lot of times we got pushback from customers on the price of OEM hub and bearings so the service advisor would save the job from walking by having us get lower price point assemblies from the parts store across the street. The service manager put a halt to that once he saw how many times labor was charged back to his department when those bearings failed within the one year parts warranty time frame. We had some of those that failed when they were on the technician's test drive. Various reasons, bad sensor, improper distance between the sensor and the internal reluctor wheel or the bearing failing itself, I've seen them that had enough play that you could shake the hub assembly.

On our own vehicles it's either OEM or in aftermarket Timken hub and bearing assemblies.

Also check tire pressure. Low tire pressure on one wheel will give you a different tire height/diameter which gives a false reading.

Anything yet?

It will make a difference if the truck has rear-wheel-only (RWAL, may still be found that year on 2wd) or four-wheel (4WAL) ABS. On 4WAL there are sensor wires clipped to the front brake hoses. Even the 4WAL is not truly four-wheel. The rear speed sensor is in the differential and reads the speed of the ring gear, not the individual wheels. If you can get in there, you can take an ohmmeter and measure the sensor's resistance at the terminals with the wire disconnected. An infinity reading (open circuit) means it is bad. You can also go over the wiring and look for chafing, chewed by mice, water intrusion into the module or whatever. Even low brake fluid can trigger ABS warnings, but the red brake light would also be on.

quote:

Originally posted by egregore:
Anything yet?

Ok, I finally got by an Auto Parts store that would actually agreed to scan the truck (due to the virus, most shops wouldn't agree to scan it). The only code to come up related to the anti-lock brake system is C1185 which upon further research really doesn't point to any real answer(s). Something else interesting is I noticed the anti-lock brake light on the dash was not lit when I left the house this morning, and came on at some point during my travels. I'm going to check each of the wheels speed sensors tomorrow to try and eliminate them from the equation.

quote:

Originally posted by greco:
Also check tire pressure. Low tire pressure on one wheel will give you a different tire height/diameter which gives a false reading.

I have a compressor in the corner of my garage and check the air pressure in all our cars on a weekly or bi-weekly basis so that most assuredly isn't the issue.

quote:

Originally posted by bigdeal:

quote:

Originally posted by Sunset_Va:
Defective wheel bearings can trigger the warning too.

I did a full brake job on the truck less than 10k miles ago and replaced all the front wheel bearings (required with the rotors/hubs) as part of the process, so I doubt its a wheel bearing issue.

It was justa suggestion. It happened to me 3 months ago, you've done a lot of work.

Jack up the front and see if there is any slop or play in the wheel. I'm still betting on one of the hub and bearing assemblies to be bad. Would not be the first I've seen.

Probably 02-03 I had a OEM hub and bearing go bad on a Saturday morning. As the dealership I worked at was closed it was time for a trip to a local independent parts store. After years of going it on their own (founded 1925) they hooked up with some dealer group. The manager who I'd known since 1968 when he started there said the only hub assemblies they presently carried were Chinese but were fine.

I installed it that evening, set a brake code within one block, scanned it, dead sensor. So Monday back to the store to exchange it. That was July, Christmas Eve that year had a scraping noise on the way into work that morning. Who wants to do a brake job outside in the snow on Christmas Eve? Not me, so I ran it into one of the tech's stalls along with a set of pads. About fifteen minutes later I get called out there, that front hub and bearing was shot, probably less than 6k on it. Off it came, OEM went on.