Need help diagnosing Brake pedal “give” at stops

[Rancho5]

New to me 2002 Sport 4x4...

When I come to a stop, as I’m almost at a standstill, (like pulling into a parking space) the brake pedal “gives” a little and then I hear a quick, small motor sound. I do stop but the “give” means it’s lurching a little. No warning lights on the dash.

I’m thinking brake master cylinder losing pressure, but I’d appreciate any opinions.

 

[fourwd1]

Refresh my memory, is the ABS built-in to the Master Cylinder on your truck?
The "quick small motor sound" makes me wonder.

For a standard MC what you describe is not a typical failure mode.

Also, xo you have a standard vacuum powered booster?

 

[Rancho5]

Refresh my memory, is the ABS built-in to the Master Cylinder on your truck?
The "quick small motor sound" makes me wonder.

For a standard MC what you describe is not a typical failure mode.

Also, xo you have a standard vacuum powered booster?

I believe the ABS is built in. It doesn’t look like a regular master cylinder. Fluid tank is wide and flat and sits on a wide box with wires going to it.

 

[BrianK14]

That is your ABS kicking in. You likely have a poor signal from one sensor (dirty, not seated properly, or going bad). When you are almost stopped, the ABS computer is sensing that wheel is locked, and activating.

 

[Rancho5]

That is your ABS kicking in. You likely have a poor signal from one sensor (dirty, not seated properly, or going bad). When you are almost stopped, the ABS computer is sensing that wheel is locked, and activating.

I will check all of the sensor connections then to see if they are seated correctly. Any clue how to tell if one is going bad? And which one? Do you know if you can buy sensors individually? Thanks so much.

 

[BrianK14]

You should check the connections, but I was meaning that the sensor itself can be not seated properly. Also gets dirty on the business end. You have to pull each one and check them.
The sensors are available from Toyota and aftermarket. They are fairly expensive. I think* each of the 4 is unique. EBay is a good source for used OEM for a resonanle cost. I would recommend that route rather than aftermarket if you need to replace one.

 

[seykotsd]

wheel speed sensor

just went through this with my 2002. hooked it up to a good OBD2 and drove around watching my wheel speed sensors and sure enough coming to every stop my one sensor was off every time. cleaned it up and so far so good but im sure ill be replacing soon enough..

 

[Rancho5]

just went through this with my 2002. hooked it up to a good OBD2 and drove around watching my wheel speed sensors and sure enough coming to every stop my one sensor was off every time. cleaned it up and so far so good but im sure ill be replacing soon enough..

I’ve got Engine Link and a dongle. I don’t think it has a wheel speed sensor option. What OBD2 did you use?

 

[BrianK14]

Second that question. Which scan Tool? And, it gave you real time data, not just abs error codes?

 

[Robb235]

just went through this with my 2002. hooked it up to a good OBD2 and drove around watching my wheel speed sensors and sure enough coming to every stop my one sensor was off every time. cleaned it up and so far so good but im sure ill be replacing soon enough..

Would love to know how you monitored wheel speed sensors via OBD?


Sent from my iPhone using Tapatalk

 

[seykotsd]

it wasn't my scan tool it was a friends. i will ask him what the brand is and get back to you, but yes we brought up the 4 wheel speed sensors and were able to drive around looking at the sensors and determine one was defiantly reading a different speed then the others were.

 

[WhiteBoomer04]

Following....

 

[gamefreakgc]

If you have a 2002, you have the fancy newer brake booster that has a built in pump. You are hearing the pump turn on but why it was not on before that I'm not sure. The older style vacuum-based brake booster operates differently.

Just a heads up, if it's the pump on it's way out the replacement is $1,200 from Toyota. However, low-mileage junkyard units do work. I used to sell them on Ebay for good money.

 

[4runner_noobie]

Same thing was happening to mine. I pulled the ABS fuse to get it to stop, because it scared the shit out of me a few time. I have yet to get around to fixing the actual problem though.

 

[Rancho5]

If you have a 2002, you have the fancy newer brake booster that has a built in pump. You are hearing the pump turn on but why it was not on before that I'm not sure. The older style vacuum-based brake booster operates differently.

Just a heads up, if it's the pump on it's way out the replacement is $1,200 from Toyota. However, low-mileage junkyard units do work. I used to sell them on Ebay for good money.

Like this? https://rover.ebay.com/rover/0/0/99?loc=https://www.ebay.com/p/656163053?iid=332671329379

So you’re thinking it’s NOT the ABS and a bad wheel sensor?

 

[Rancho5]

Same thing was happening to mine. I pulled the ABS fuse to get it to stop, because it scared the shit out of me a few time. I have yet to get around to fixing the actual problem though.

So your fuse is still out? No ABS for you?

 

[Rancho5]

Here's a simple test for the brake booster.
Found this on a search. It’s from a 2nd Gen though so I have no idea if it’s applicable.

“With the motor off, pump the brake pedal until it is firm. Once it's firm, hold the pressure on the brake pedal. While holding pressure on the pedal, start the engine. If the pedal does not sink down then the problem is your brake booster. If the pedal does sink down then I would look into your master cylinder.”

So I did it and the pedal sank. Does this help for my 02 at all?

 

[gamefreakgc]

Like this? https://rover.ebay.com/rover/0/0/99?loc=https://www.ebay.com/p/656163053?iid=332671329379

So you’re thinking it’s NOT the ABS and a bad wheel sensor?

That contraption is your ABS system. Checking the wheel sensors is easy if you want to rule them out. They are held in each axle by one 10mm nut, just pull the sensor out (there's a tab to fit a screwdriver in to pry them out) and make sure the magnets are clean and the rings are not damaged. Do that for all 4 wheels and go drive like normal.

Normally a bad wheel sensor will cause your ABS light to turn on, such as if the wiring was accidentally cut.

 

[seykotsd]

asked the guy he said the brand is Autel. he bought it for around $250. hope this helps!