Service Brakes Soon shortly after replacing caliper

[olliec420]

Left (driver) rear caliper was sticking intermittently. Replaced it last weekend no problems. Checked other pads ok but right rear was done. Had been smelling hot brakes off and on for a while but couldnt pin it down til last weekend. So all good, riding great. On the way home today, probably about 120 miles after the caliper replacement and get the message "Service Brakes Soon" on the interstate on the way home. Got home, fluid level is good. Whats next to check? Could be air in the system? I gravity bled it just like the TRQ video.

 

[OBSandaNNBS]

Right rear caliper was sticking intermittently. Replaced it last weekend no problems. Checked other pads ok but right rear was done. Had been smelling hot brakes off and on for a while but couldnt pin it down til last weekend. So all good, riding great. On the way home today, probably about 120 miles after the caliper replacement and get the message "Service Brakes Soon" on the interstate on the way home. Got home, fluid level is good. Whats next to check? Could be air in the system? I gravity bled it just like the TRQ video.

Being the right rear, that is rather unlikely. You only bled the right rear afterwards, correct?

PS you totally tripped me up with that beaut of an OBS Yukon on your profile pic.

 

[olliec420]

Being the right rear, that is rather unlikely. You only bled the right rear afterwards, correct?

PS you totally tripped me up with that beaut of an OBS Yukon on your profile pic.

Sorry, driver rear! So left rear. I cant believe i did that whole post wrong.

And to add, I just put the scanner on it, here are the results. (I didnt take a pic but brake booster pressure was steady at -8.8X PSI idle in park and went up with throttle.

Oh and to add, I have 800 miles trip on Monday. Got to deal with this now if its a problem. Hopefully its something simple.

P.S. Thanks, yes its so nice. the paint is starting to look like the sun is doing a number on it, project #1 for cooler weather is to get a cover for this thing built asap.

 

[OBSandaNNBS]

Sorry, driver rear! So left rear. I cant believe i did that whole post wrong.

And to add, I just put the scanner on it, here are the results. (I didnt take a pic but brake booster pressure was steady at -8.8X PSI idle in park and went up with throttle.

Oh and to add, I have 800 miles trip on Monday. Got to deal with this now if its a problem. Hopefully its something simple.

P.S. Thanks, yes its so nice. the paint is starting to look like the sun is doing a number on it, project #1 for cooler weather is to get a cover for this thing built asap.

You said the brakes are functioning well, but I think that 9 PSI sounds low. Confirm that range.

So if those two things are true, sounds like the vacuum boost sensor could be acting up. Timing of that is a little weird...

But if not, sounds like you have a leak around the booster.

I'd check to make sure nothing was bumped or bothered around the booster first. Listen for a leak.


Yeah I was like, oh crap, he swapped 4 wheel discs in!

 

[olliec420]

You said the brakes are functioning well, but I think that 9 PSI sounds low. Confirm that range.

So if those two things are true, sounds like the vacuum boost sensor could be acting up. Timing of that is a little weird...

But if not, sounds like you have a leak around the booster.

I'd check to make sure nothing was bumped or bothered around the booster first. Listen for a leak.


Yeah I was like, oh crap, he swapped 4 wheel discs in!

So the other day I did that caliper, oil change and while i was under the hood I was spraying brake clean at the intake gasket and pcv line boots, throttle body boot and the brake vacuum hose looking for leaks. Dont hear any but it feels low on power under 3k rpm and some occasional rough idle so I was thinking there may be a vacuum leak but I did not find one.

I'll check again. Do we know what the brake booster psi vacuum should be?

Quite a coincidence since I just did brake work.

And it says fluid is low but it is not.

 

[Fless]

And it says fluid is low but it is not.

So something is wrong with the fluid level sensor or the circuit. While you have your scanner on it, pull the connector off of the level sensor and short the two harness contacts. The scanner reading should change from LOW, which would tell you that the sensor is bad.

If it doesn't change, there may be a circuit issue. You can find wiring diagrams on www.charm.li.

 

[olliec420]

So something is wrong with the fluid level sensor or the circuit. While you have your scanner on it, pull the connector off of the level sensor and short the two harness contacts. The scanner reading should change from LOW, which would tell you that the sensor is bad.

If it doesn't change, there may be a circuit issue. You can find wiring diagrams on www.charm.li.

Shit, I cleared it to see if it would come back. I'll do if when it comes back.

 

[Fless]

It's probably a hard fault so if you turn the ignition on, it should show up on your scanner as LOW.

 

[olliec420]

This morning went to head out and the message came on again in less than 5 minutes from leaving. Quick inspection around the booster and master cylinder have no obvious signs of leak and brakes feel fine. Will check for more later but does anyone know, does that code C0299 possibly have anything to do with air? Or is it going to be closer to the stuff under the hood? I wish it hadnt come on a week after brake work. Makes me think its a result of that instead of something randomly going wrong.

 

[rdezs]

Sounds like the fluid level sensor in the master cylinder. Probably not a coincidence. Fluctuating brake fluid levels while bleeding probably disturbed the sensor from where it's been sitting for a couple years.

 

[olliec420]

New clue: Im only getting the message popup on the interstate. I live rural so I have to take the interstate or other highways to go anywhere. After i clear the message and drive around town, nothing everything fine. Back on interstate for 15-20 min, and service soon message comes up. Does that help us know whats going on any?

 

[Fless]

SWAG: Maybe there's vacuum leak that has compromised the ability of the brake booster to provide assist.

 

[olliec420]

SWAG: Maybe there's vacuum leak that has compromised the ability of the brake booster to provide assist.

Do we know what the pressure should be? Does anyone have a scanner they can check theirs and let me know? Mine was reading -8.8X at idle in park. Going lower with more throttle of course.

 

[Fless]

You likely need a scanner that will give you the code suffix (unless for some reason I'm not seeing it on your pics) in order to narrow down the cause.

See the link below, but verify your specific vehicle and navigate to the code diagnostic page that is similar:

C0299 — 2009 GMC Yukon 4WD V8-5.3L Service Manual | Operation CHARM

Detailed repair manual for the 2009 GMC Yukon 4WD V8-5.3L.

charm.li

 

[OBSandaNNBS]

Do we know what the pressure should be? Does anyone have a scanner they can check theirs and let me know? Mine was reading -8.8X at idle in park. Going lower with more throttle of course.

My crappy scanner won't read vacuum, and I don't have a vacuum gauge.

But apparently, from some research, 17-22 inHg is the range. Notice if you don't pay attention to units, there is a good chance to think you are running low. Ask me how I know! This converts to from 8.4 to 10 PSI.

So it seems that is OK.

 

[OBSandaNNBS]

New clue: Im only getting the message popup on the interstate. I live rural so I have to take the interstate or other highways to go anywhere. After i clear the message and drive around town, nothing everything fine. Back on interstate for 15-20 min, and service soon message comes up. Does that help us know whats going on any?

Did you try unplugging the brake fluid level sensor and comparing the scanner result?

I join @Fless and @rdezs in suspecting that sensor.

 

[mikez71]

@Fless layed it all out!
Cannot do all charm.li steps without better scantool. But can rule out the first part since the light doesn't come on right away. Little leak, while cruising down highway doesn't generate enough vacuum to keep it where it wants like Fless said.

-8.8psi at idle fine, but what does it read cruising down the highway?

A tidbit I read today about the booster sensor fom 'blindsquirrel ' on hptuners forum..

'Booster sensor is only used to disable DOD if vacuum is lost on the other side of the check valve, so only the auto trans cars with DOD have the sensor. The manual ECM has no reason to even have the code in there to read it.'

 

[olliec420]

So Im back from my trip late last night. The message appeared right when I departed on Monday and then I never saw it again. I havnt had time to do any more digging but Im thinking since it has not reappeared, maybe it was a small bubble that worked its way out? Maybe the sensor acting right now? I found a resource that said that code can come from air in system. Anyway, I will keep an eye on it and try to find a scanner that will give the suffix. Thanks!

 

[olliec420]

Did you try unplugging the brake fluid level sensor and comparing the scanner result?

I join @Fless and @rdezs in suspecting that sensor.

Not yet but I will this weekend.