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Brakes pulse briefly after starting engine Cold or Hot. Also need a brake bleeding scan tool?

2006 Chevy Malibu Maxx. This just started a little while ago, before I replaced front brake pads. after I start the engine whether cold or hot, the brakes will pulse briefly when I step on them to get the car in gear. It feels like the ABS, but it only does after a fresh start, and not when braking. The car stops fine. The brake pedal is a little spongy, probably because I didn’t bleed them, but the pulse was already happening so I don’t think they are connected. there are no warning lights on at all. Also, it doesn’t do it 100% of the time, maybe 80 to 85%. any ideas?.

In order to bleed I guess I need a scan tool, but the bleeding procedure is a bi-directional function which is not supported by most of the gizmos available. Know of one that might work without spends thousands?

The ABS will run a self test on itself each time the vehicle is started be it hot or cold. So that could be the pulse in the brake pedal.

It’s recommended that the brake system be pressure bled. So you need something like this http://www.ipdusa.com/products/4678/109285-motive-power-brake-pressure-bleeder with the proper brake master cylinder adapter. Then turn the ignition switch on so the dash lights come on, step on the brake pedal a half dozen times to dump the reserve vacuum out of the brake booster and set the solenoids to their home positions in the ABS pump. Turn the ignition switch off and bleed the brakes under pressure.

Don’t step on the brake pedal until the bleeding is complete and all bleeders are closed.

Tester

I built my own pressure bleeder, ready to go, I’m worried about air in the ABS module. The only way to cycle the solenoid is with a scan tool that can communicate with it. I’m going to power bleed without it and see what happens, the dealer will do it for $82 but I’d rather do it myself.

Good thought about the self check, but the car didn’t do this for 4 years, then all of sudden started so I think self check is out.

Pressure bleeding didn’t do anything, so symptom with the pulsing brake pedal. Any other ideas?

The valve in the ABS modulator should be wide open when not energized. Pressure bleeding is definitely the way to go, because with the modulator involved there’s no longer just straight lines, there’s cavities. however the system should bleed fine with a pressure bleeder.

Since your ABS hasn’t stayed lit suggesting a code, I’m wondering of the shudder is coming from something mechanical like a sticking master cylinder piston. That would tend to disappear once used iun the morning. Or perhaps a sticky pushrod (from the pedal through the booster and into the MC). Tester, have you any suggestions on how this can be checked without removing the MC?

One more thought: does it do this still with the ABS fuse pulled?

Pressure bleeding did make my brake pedal feel much smoother during braking, but the initial pulse is still present. Someone else told me it might be a sticky piston in the front caliper so I got two front calipers to replace with, I’ll be installing them this weekend. My initial thought was the master cylinder but I’ve had three mechanics tell me the master cylinder is fine… :frowning:

I will test this with the ABS fuse pulled later today and report back.

I think that its ABS self test, as Tester noted, and that if you pull the fuse as mountainbike suggests you’ll probably find the symptom gone.

However, if that doesn’t do anything, then one other thing that might be worth a look is the check valve for the brake booster. If it was getting a bit squirrely it might not be holding vacuum perfectly, and perhaps stuttering a bit as vacuum operates on it. When you first start up the car is when the vacuum is being replenished. If the engine or valve are even a little squirrely you could be feeling something of an effect from varying vacuum force.

Like I said, I think Tester is right and this is a long shot. But its not outside of the realm of believable.

What has made you rule out the ABS self-test? It’s very common to feel a pulse in the brake pedal when the test runs.

He said it was a new behavior after 4 years of ownership.

Ah, missed that.

I pulled the ABS fuse and the pulse went away… Now what? Does that mean my ABS module is bad?

Is it malfunctioning? By which I mean, is it activating when it shouldn’t, or failing to activate when it should?

I’m still wondering, honestly, if it’s just the self-test. I have a friend with an Acura RL who finally noticed the test pulse after owning the car for several years. Are you sure that’s not what happened here?

My own theory is along the lines that shadowfax mentioned. Its been there all along, but after changing the brakes you got hyper-sensitive/vigilant - which is wise and understandable.

If its doing this AND if the ABS light isn’t staying lit up on the dash AND if the brakes are not otherwise acting oddly, then I’d be inclined to say that you have no problem with anything.

Since the symptom disappeared when the ABS fuse was removed, I’m inclined to agree with Shadow and with Cig.

I understand what you guys are saying and it makes sense, but I really don’t think I would have missed this pulse feeling for years. Is it possible that the pulse could be stronger or more pronounced do to age/looseness/tightness??? Also, I did feel this pulse before I replaced the pads my self and it does not do it 100% of the time. In fact I was camping last weekend and it didn’t do it from Friday until Sunday, then all of a sudden on Sunday it’s been doing it again ever time since, except for when I pulled the ABS fuse.

OK here is an update with a new Twist. I KNEW IT WASN’T JUST ME BEING HYPER SENSITIVE.

I recently had a grinding sound so I took the pads off to see if I had wear already, but I did not. I also installed new hardware and grease.

I could not get the pedal stiff again, so I grudgingly brought the car back to the dealer for a pro-bleeding, with their fancy computer. They called me and said that they could not communicate with the computer on the car, and would need to do a full “Diagnostic” to determine why.

What they found, or claim to have found, is that my after market stereo is the cause for this. I’ve have my Sony stereo installed in the car almost as long as I’ve had it, for 5 years, and I’ve never had a problem, or had anyone tell me this was a problem. They were able to communicate on e they disconnected it and they complete the bleeding.

Since I’ve gotten the car back the pulse in my brakes is gone, it hasn’t done it once in over a week. I’ve also noticed that my cruise control now works again, it hasn’t worked in while, but I almost never use it so I’ve hardly even noticed it or thought to mention it.

Now here is my new question, Should I believe that the stereo is really the issue, or is there something else, that has caused these glitches, and the stereo just happens to tie it all together.

It could be the stereo, yes. Modern cars are oftentimes fully integrated to levels you would never expect. My TL’s radio/nav unit is integrated with the ECU and the climate control, for instance, so that the nav system’s solar angle sensor can tell the climate control to blow the fan a little faster on the side of the car facing the sun.

Saying that you’ve never had a problem isn’t totally accurate when you then say that disconnecting the stereo got you your cruise control back :wink:

It wouldn’t surprise me (and this is just a wild guess) if the stock stereo has a memory module that stores various diagnostic tests for uplinking to diagnostic equipment or possibly via cell phone to the factory. If so, then removing that memory would make your car think it hasn’t run a full ABS test in awhile, which causes it to run one every time you start the car.

Unfortunately, aftermarket radios are becoming harder and harder to install because of the amount of integration in cars. Fortunately, factory radios are no longer tinny-sounding suckfests like they used to be.

The entertainment center is directly connected to the Body Control Module or BCM. The BCM is the gate keeper for the Controller Area Network or CAN. If the aftermarket entertainment center messes up the signal between the BCM and the CAN, the BCM will no longer communicate with or recognize the modules in the CAN. I can see it happening.

Tester