Brakes suddenly mushy, then back to perfect. Brake MC or ABS issue?

2008, 5.7L, 90k miles.

Had this truck a bit over a year now. Pretty much flawless for me so far.
I use it for landscaping, which is mostly light duty, but started pulling some occasional weight recently.
Usually pretty gentle and careful with the truck.

It drove perfectly fine. Parked it.
Started it up 45 minutes later and immediately the brake pedal went down much further than usual. I noticed it immediately and thought I had a ruptured brake line or something. Did a quick check, everything looked good. Brake fluid was not low.

Limped it home. Brake pedal went to the floor, had 40% braking power.
Shut it off. Looked underneath. No leaks.
Started it up, pressed the brake pedal with my hand several times while looking under. Nothing.

An hour later, unhooked the trailer, drove it around the block, brakes are perfect again.

Some people are suggesting it's the brake master cylinder gone bad, but I can't see how that would be sporadic?
Some people mentioning something about issue with the ABS system...ugh.

Someone said this is a common issue, but I can't find reliable information about it.

 

any lights ? usually ABS system will trigger a bunch of lights.

 

no lights. I thought that was odd too. Just the mushy brake pedal and that's it.

 

I’m leaning toward abs module. Master cylinder typically hisses if it’s bad when you press on the brakes.

I know this is not a Toyota, but wife’s Lincoln just had abs module go out with similar symptoms. Also didn’t trip any lights.

if you opt to replace it yourself, which you should since it’s easily accessible, you’ll need a special scanner tool to activate abs self bleed procedure. Otherwise you won’t get the air bubbles out of the abs module as the valves would need to open up.

 

Is this a common problem on the 2nd gen Tundras?

Is there any way to diagnose the ABS module? It sounds expensive...
Does anyone know if it's a software issue randomly acting up? Or maybe a valve/seal going bad internally?
I wonder if they can be rebuilt...

 

Based on my research when my wife’s car has this issue, a few people suggested driving on a road where you can lock up your brakes to trigger the ABS to pulse. Sometimes a sticky solenoid valve would unstick and give you full brake pedal back. Personally, I think that’s a band aid “fix” and you may as well replace the module if that’s the culprit since I’d imagine it can stick again and maybe not at a time where you’d want it to stick.

Attached photo is my wife’s ABS module removed. I don’t know if this thing can be rebuilt though. It was pricey around $450.

 

Also, the scanner that I used to bleed the system is Foxwell NT630 that I bought on Amazon. It looks to have an menu option to test solenoids and run abs codes but I didn’t get it until after I swapped the abs module So I don’t have much experience troubleshooting they system with this scanner

 

Thank you for posting about the ABS module. I tried to 'purge' the ABS pump several times by locking up the wheels. It has had no change.
I previously owned a BMW that had the 'trifecta' lights: ABS, brake, and traction control. This was the dead giveaway that the ABS module had failed. The computer circuitry inside had gone faulty, due to a bad solder joint or such. But you could send those in to be repaired to some company that did micro solder work. Not sure, I never did it.

I thought maybe my truck had a similar issue, especially since it's black and has been very hot out. Maybe the heat caused the circuit board to fry.


Anyway, locked up the wheels several times with no improvement.
I bled my brakes. The pedal feeling got slightly better, but still unacceptable. It's just dangerous, to be honest.
I will bleed them again, but I'm suspecting I'm missing something at this point such as an ABS bleed function activated via techstream or something.

I'm not even sure your scanner will give me any capabilities/functions that I don't already have access to, but would you consider letting me borrow/rent it if it might help me out?