ABS Code 49 Help!!!

Okay, I have some additional info that might help me or someone else down the road. I mentioned above that on occasion I have been able to drive 20-30 minutes and not had the light come on. So I got to really thinking about that this morning, why, what's different?? A/C, that's been on the last two months. HEADLIGHTS, what if I turn headlights on does that make a difference.

So I tried it, I left the house, headlight switch on, middle of the day, drove 18 minutes, NO ABS light. Stopped, ran errand, then went to next errand, drove 15 minutes, NO ABS light. Stopped, ran next errand, then on to next location, 7 minutes, NO ABS light, then on to the house, for final leg of 6 minutes, and NO ABS light there either.

I'm onto something here I believe, but why, what the hell difference does ABS care if headlight switch is on or not????? Normal configuration, starting truck and put in gear or rolling forward, headlights turn on by themselves, although I don't think they are as bright as if you turn the headlight switch on itself. Other differences, tail/marker lights, they are not on normally but they do come on when you turn headlight switch on.

I'm still confused as to why this would make a difference, a voltage bleed through, a high resistance at a headlamp socket or relay, IDK, but something is tied in here between the headlight circuit/stoplight circuit and ABS giving a flying F%&@.

I need to look at more diagrams and more testing, but if anyone has thoughts on it, I'm all ears.

DopuS said:

I don't have anything constructive to suggest, but out of curiosity, what does it take to pull the ABS code(s)? I have been meaning to check mine as my light is on.
Thanks and good luck

Click to expand...

I think it depends on what year truck you have, for example my truck is a 2000, it does have the obdc plug in but that is only engine/emission related codes that come up on my scan tool. Nothing about ABS.

So on my truck there is a little black box with a cover that is sitting to the side of the intake manifold/plenum slightly towards the driver side of the engine compartment. I believe it's technical name is DLC1. You open the cover and they have terminals routed for testing different systems like ABS, cruise control, etc.

In my case, maybe yours, you probably need to see the FSM for your year but I jumper pins TC and E1 and then look at the dash, the ABS will flash slow and not flash then flash again a number of times to give you a number. So 4 slow flashes with a few second pause then 9 slow flashes equals code 49 which is what I have.


Possible corroded ground or poor connection at the ABS module, try removing the large connector and cleaning the terminals.

Pin 24 at the ABS module connector is the STOP voltage signal from the stop light circuit..
Do You have a trailer harness adapter ??


Pm me if You want to come by the shop SaturdaY afternoon, (I'm in Alvin) we could dig around and maybe see what the problem is..
We can see the datalist and maybe shed some light on the ABS light..

Thanks Jomentum for the info man. I have taken that big ABS connector off, cleaned it with contact cleaner and applied a electrical or diaelectric grease to the female sides and reseated, made no difference. A ground? Possibly you are right, I see a fender ground that looked like it dealt with ABS actuator, I do want to put a meter on it, clean it and reseat it, good suggestion.

Trailer Harness, yes I do, I looked at that two days ago, I unplugged the harness pigtail cleaned the contacts, and applied diaelectric grease to both right and left pigtails, excellent suggestion, I thought for sure that was gonna do it, but it made no help. I am throwing a thumbs up to u for the invite for ripping and tearing Saturday, I'm working this Saturday but keep the invite open for me for future reference and I'll reciprocate my friend.

Fast Frank, your reply goes kind of hand in hand with Jomentum, grounds can cause all kinds of havoc, I tried to do some shakey shakey while having a meter on different areas but there are a few grounds I do want to look at closer...

I do have an update, I just found this morning, quite possibly the problem, or at least a portion of the problem.
I pulled up the Headlight WDG's last night, and traced out one for headlight switch on and one for DRL (daytime running light) which is headlight switch off but in dim mode.
After looking at the two, there are a couple differences in circuitry pathology, and one item in particular struck me at top of the list. Sitting over by the battery box is a DRL Resistor, not in use with headlight switch on, it's suppose to read 337 Mega ohms, so I throw my meter on it, I got .50 Ohms, not kilo, not mega but a half a ohm, this resistor is fubar. I ordered a new one, but, I'm not putting in until I can verify some grounds and a couple relays are functioning like advertised, to make sure I don't blow a good resistor.