ABS check light

2004 Taco Prerunner..... 202K miles.

If my abs pump/system is bad.... would this not throw a check engine code? Had it scanned and it showed 0 codes.

Not able to keep my brake pedal firm. Keeps slowly sinking to the floor. Replaced the Master Cylinder twice. No change. I have not had the ABS system bled yet.... (bled the regular brake lines many times) if there is air in the ABS.... would this throw a code? Confusing since there is no code at all. Code meaning check engine light of course. So without a check engine light for the ABS system... would this not mean it has no air and has no problems otherwise? Confused in Taco land....

 

for the brake pedal slowly sinking... is there any play in the pedal and pushrod into the brake master cylinder?

 

No I would say not... nothing noticed anyway. Seems normal. Brakes seem good and tight for a day or so after replacing the Master Cylinder then begin to get soft again.... Several mechanics that I know have mentioned the possibility of air in the ABS system... but since after scanning the truck for codes they found only one issue related to an o2 sensor. Nothing related to the ABS. I was trying to find out if the ABS pump/block did have air... would this throw a code? The ABS light on the dash never comes on. If is doesn't throw a code for simply having air in the system this might be the issue. Might invest in a reader and do the bleed of the ABS myself if it's a good chance that's what it is. If it's the ABS system itself.... hmmmm.... big bucks.

 

I do not know if in 2004 there was bi-directional control in the OBDII protocol for actuating the ABS pump for bleeding the system. If there isnt you can activate the the ABS pump by driving 15 - 20 mph on a loose dirt gravel road and a stomping on the pedal... anything that will allow for a front wheel to travela at a different speed than the other front wheel. Kind of p.i.t.a. but it works.

 

I'm not positive either but I think I've read that air in the lines will not throw an ABS code on these. Or is that backwards??? No, no, I think that's right. I think you can have air in lines without ABS error or code being thrown

 

Thanks, at this point I think I'll give that a try on some wet grass... beats buying a scanner and then finding it doesn't have the program in it. I know that quite a few Toyota vehicles have this issue. Tried to run the ABS bleed program on a RAV a couple of weeks ago and found it didn't have the ability to run it. Actually I was just helping the guy with the scanner... but if this doesn't work I may try and get the scanner back to give it a try...or just buy an Autel model.

 

I was told it would throw a code but I think you must be right. Obviously I have air in there somewhere and I really suspect the ABS at this point.

 

My abs does not function. I have the abs light on but no check engine light. Been that way for a year now. Not sure if that answers your question or not but that’s my two cents.

 

I searched through my emanuals and all I can come up with is stuff for a 2003 and 2005... 2005 has lots more electronics to control skip,slip etc and I feel it is a totally differernt system... the 03, not 100% sure but I have attached the brake section.

 

I will go through it, thanks. At this point after skidding around the field inducing ABS tremors and bleeding and bleeding and bleeding... I still have a soft pedal that will slowly sink to the floor. It appears I have a bad ABS something or other. Probably a grand or more... oh joy. For the last 3 years when I stop the rear axle tries to roll up on itself which is so annoying...then falls back down when at a complete stop...figured this might fix it all. But, no joy. Time for the big bucks I guess.

 

Nice looking truck.

 

before I would spend large $ like that I would test each component.

I had a buddy who had a very expensive sand rail >$75k and he had a similar issue fading brake pedal. Each shop he took it to came back with the same BS... they all put in new master cylinders and bleed gallons of brake fluid through the system. He was telling me about it over the phone one eve and I said drop it off... I cant do any worse. Reluctantly he did and I spent a bit of time finding the correct plugs for all of the hydraulics... this thing had electric parking brakes, turning brakes etc, lots of things to check. I plugged the master cylinder ports first, rock hard pedal, then the shortest line off the front port, rock hard pedal, then the next and so on. What it turned out to be was a manufacturing defect* on the RR caliper where the 2 halves bolted together. It would suck air on pedal return but wouldnt leak a drop on pedal pressure.

*the defect was one of the o-rings that seal transfer holes on this 4 puck caliper was machined just a little deep so the o ring didnt have enough squish. CNC couldnt really answer the "why" question but thanked me for my discovery and gave me a new caliper... my buddy was jazzed.

 

Amazing.... will have to give this a try... can't hurt. Where do I find these plugs?

 

that was THE problem. Some of them were bolts some were brass plugs from the suto part store some were from the brake manufacturer, CNC and were common according to them but I couldnt find them. If the port was just a port, a correct threaded bolt would do, if the port was a reverse double flare metric... that was an issue.

 

What MFing thorough diagnostic skills hombre that's some good info for you to share and me and others to absorb, the part on isolating the individual components for testing. I love this, this is one of those repairs that common folk don't care but anyone who's worked in it hears this repair and

Edit: did the caliper happen to be a big name brand made one? You recall?