Grumpyf150xlt

Have read thru the forums and haven't found an answer yet.

After recently having master cylinder replaced and a rear brake job my RABS (not 4 wheel ABS) light is on. Occasionally, as I am driving, it will go off and stay off until the next time I start the truck. Even then sometimes it will stay off. When it does come on it will do so when the truck is first started before I have driven it at all. I have replaced the rear sensor and the problem remains.

Brake pedal is nice and firm, not mushy and does not bleed down. Master cylinder is full of fluid. Brakes have been bled and bled and bled.

Brake light itself is not on, just the ABS light

Any ideas, solutions appreciated

1997 F150 XLT, 172K, 5.4 Triton (short plugs)

rmh

What does the Owner's Manual say? It sounds like the sensor is bad, or going bad.

Grumpyf150xlt

Replaced the sensor today with a new one. Problem is still there.

RLXXI

Most common problem would be the wheel speed sensor on top of the rear end, then the master cylinder float switch. Then the rabs valve on the frame just under the driver door. You can take a chance replacing it but there is a series of tests you can do with a dvom to be sure.

If you do a search thru my posts you will find where I walked someone else thru the diag.
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Grumpyf150xlt

Replaced the wheel speed sensor on top of the rear end today with negative results.

The master cylinder float switch appears to move freely, not sticking to the bottom at all. Master cylinder full of fluid to Max Line.

I searched thru all 494 of your posts and found nothing as far as the procedure that you refer to. Maybe I missed it somehow, I don't know.
Could you please help further?

As a side note my Cruise Control doesn't work either.

All other systems work fine. Horn, A/C, Auto Lights, Wipers, etc. No other warning lights on. Have pulled instrument cluster as I had to replace odometer gear and replaced all lights at that time. Bench tested all and all were good.

Purchased this truck (1997 F150 XLT, Trailer towing package) approx a month ago (for $2,200.00) and have corrected several issues on it so far. Alignment, new front end parts, 2 new tires, rear brake job, new master cylinder, replaced headliner with Mossy Oak headliner fabric, repaired cracked dash and re-finished it. Added Flowmaster exhaust. Replaced plugs (fortunately I have the short ones) replaced coil on number one cylinder as it was bad. Did accent paint on center wheel caps (small mod but looks good) re-charged A/C (blows nice and cold now) and installed after market radio with blue tooth for hands free calling.

Truck has straight body and good paint. Runs fantastic. Planning on Gotts Mod, new seat covers (Mossy Oak from Coverking) and some fog lights.

My last two issues are the ABS light and the Cruise. BTW, it does have a trailer brake controller.

Thanks in advance for your help.

deanfx

Was the ABS light on before you changed the master cylinder?

RLXXI

Probably did miss it considering I have over 5000 posts in this forum. It wasn't a post I made, just one that I replied to.

Does the red brake warning light come on and then go off after you start the truck?

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clearnetedm

This may sound really dumb as I'm not a mechanic at all. But I recall a while ago some vehicles would not allow cruse to work if a rear brake lamp was burnt. Would or could that cause the abs light and maybe your cruse issue? Maybe that was just urban legends?

Grumpyf150xlt

@Rnlcomp
As I recall it was not on before changing Master Cylinder.
No Red brake light comes on at any time.

BTW, found your previous posts:
https://www.f150forum.com/f10/96-2wd-abs-light-195552/
https://www.f150forum.com/f12/yet-an...estion-224105/

Very informative and detailed. Should be a sticky.

Particularly liked your suggestion of by-passing RABS and removing dash light. LMFAO, that's the way to go.

@clearnetedm
All brake lights are good and I am not running LED's.

RLXXI

The rabs system was never known to work well even when it was functional. On the master cylinder switch there should be 3 wires, one is black and that's ground. The other two wires, tan/light green and dark green/yellow can be jumped together with a small paper clip or other wire and taped back to the harness to see if the light goes out and stays out, if it does there's the problem. If not try the diag steps already posted.

The posts above may or may not be identical for your truck as that was for a 96, completely different truck so if you run into something using those diag steps and something don't match let me know.

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