Recall - Vacuum Pump May Decrease Power Brake Assist

BuffaloGMCSierra · December 9, 2019

I took my 2017 Sierra in a few months ago for the reprogramming. A few weeks after the reporgramming, while I was backing up in a parking lot space, the ABS triggered everytime I pushed the brake pedal. It was a once occurance which I could not replicate again. Since then, over the weeks, I noticed that the ABS would start triggering sporadically when I was pulling up or backing out of my slighlty sloped driveway. I figured it was the vacuum pump going bad.

I scheduled service and took the truck to the local dealership. The service advisor was knowledgable on the problem and was able to replicate the slow speed ABS trigger quickly. My truck is beyond the bumper to bumper warranty but my service was covered under the extended brake recall warranty. The vacuum pump was replaced within a day. I was worried it was going to be a back ordered part due to the strike.

It has been a few days since the service was completed and I have not had any more issues. I hope the new vacuum pump was manufactured by a diferent company or improved upon. We shall see if anymore problems show up...

Edited December 9, 2019 by BuffaloGMCSierra

flyingfool · December 10, 2019

i would like to get some vacuum readings from you guys with new pumps to compare to the stock pump., my pump only pulls 3-5 in.ches of mercury on the freeway in v4.

come on i need some data

David Crandall · December 10, 2019

10 hours ago, flyingfool said:

i would like to get some vacuum readings from you guys with new pumps to compare to the stock pump., my pump only pulls 3-5 in.ches of mercury on the freeway in v4.

come on i need some data

What are you using to get this reading, and what sensor are you reading for this? I think you're going to have to be looking at the ABS module to read the vacuum at the brake booster and see mechanical pump output.

If you are getting this low reading only with the engine in V4 mode than you are not reading what the vacuum pump is doing. Lack of vacuum supply to operate the brakes with the engine in V4 mode is why the mechanical pump is there. Service manual specifications for engine driven mechanical vacuum pump readings are 27 in Hg or greater at idle in park with the AC off.

I'm pretty sure that if the vacuum pump was producing so little vacuum you would be getting some kind of a warning to service the brake system.

Previous generations of the trucks didn't have the mechanical vacuum pump and would deactivate the active fuel management system if the vacuum was too low for proper operation of the brakes.

Edited December 10, 2019 by David Crandall
Auto correct errors

JoBo1943 · December 10, 2019

As I understand it this problem only manifest's itself in slow speed situations like parking lots and so forth when the engine would not be in the V4 mode.

SILVER SLED · December 10, 2019

The special policy N182202780-01 now covers the vacuum pump failure for 10 years or 150,000 miles on.

flyingfool · December 11, 2019

I'm using a $7 ELM327 blue tooth obd2 module , Amazon or ebay has them, connected to a $20 android tablet , running "torque: app, the lite free version or the $10 full package software both work fine. i run live data mode while driving, and I select my manifold vacuum sensor in the truck.

the lack of vacuum supply is not an issue because there is a check valve holding full vacuum in the brake booster tank. but if you have a leaky check valve than you have major issues in v4 mode. quick remedy is to shift into m5 mode on the trans, this will kill v4 and go full v8 and produce a full 20-22 inches of ENGINE vacuum.

Edited December 11, 2019 by flyingfool

Jglew82 · December 11, 2019

i would like to get some vacuum readings from you guys with new pumps to compare to the stock pump., my pump only pulls 3-5 in.ches of mercury on the freeway in v4.
come on i need some data

I believe you are only reading manifold vacuum
Which is not indicative of what the brake vacuum pump is doing since they are separate. Those numbers are typical in V4 mode for the engine, however.

flyingfool · December 11, 2019

21 minutes ago, Jglew82 said:

I believe you are only reading manifold vacuum
Which is not indicative of what the brake vacuum pump is doing since they are separate. Those numbers are typical in V4 mode for the engine, however.

your right I'd like to try and figure out a way to tap into the pump somehow

Grumpy Bear · December 11, 2019

12 hours ago, flyingfool said:

your right I'd like to try and figure out a way to tap into the pump somehow

"T" into the line between the vacuum pump and the booster can and add vacuum gauge.

David Crandall · December 11, 2019

16 hours ago, flyingfool said:

I'm using a $7 ELM327 blue tooth obd2 module , Amazon or ebay has them, connected to a $20 android tablet , running "torque: app, the lite free version or the $10 full package software both work fine. i run live data mode while driving, and I select my manifold vacuum sensor in the truck.

the lack of vacuum supply is not an issue because there is a check valve holding full vacuum in the brake booster tank. but if you have a leaky check valve than you have major issues in v4 mode. quick remedy is to shift into m5 mode on the trans, this will kill v4 and go full v8 and produce a full 20-22 inches of ENGINE vacuum.

What you are reading has absolutely nothing to do with the vacuum pump, or brake booster. They are not linked together in any way.

I have a similar device but am using the paid version of the car scanner app. I used torque for a long time, but like this one better. Works great for quick stuff at work to determine if I need to get the shop scanner, or basic stuff at home. It will take a more advanced scanner to read it since it will not be standard OBD II data. It's going to be read in the brakes module.

The vacuum pump was added to these Ecotec3 engines to provide a constant source of vacuum to the brakes regardless of active fuel management operating mode. When they start to fail it is most evident at low speed because the pump is belt driven, so output is decreased. The vacuum check valve is still there for the same reasons it was when using manifold vacuum.

15 Z71 · December 12, 2019

Seems like alot of people that have had the recall done are the ones now having issues. I have not had mine done dont know if I will after reading all the problems after recall was done. My breaks work great now.

Spurshot · May 17, 2022

Interesting old thread. I finally took my 2014 in for this about the beginning of 2020. I told the dealer I had experienced loss of brake assist numerous times. The GMC dealer said they'd do the software update. They gave it back to me and said that the pump tested fine and they don't replace pumps unless they test bad. Sounds suspicious.

However, I have a leak somewhere on the front cover and I'm likely to be digging into it, so I'll just change it when I have things apart.

NWI Denali · May 23, 2022

2017

Had the "recall" refresh done Oct 2021. Just started getting the hard pedal/loss of power assist at parking lot crawl a month ago. Dealer replaced pump and new belt under warranty. They seemed pretty aware of it. Service writer said he has one tech who has done 200+ of them. Keep in mind this is a small town dealer too lol.

Robopie · June 7, 2022

My 2016 is having this issue, and not in warranty and not part of recall. What exactly was the fix so I can do it myself?

mikeyk101 · June 7, 2022

10 hours ago, Robopie said:

My 2016 is having this issue, and not in warranty and not part of recall. What exactly was the fix so I can do it myself?

Not sure why yours wouldnt be included in the recall. As far as replacement of the brake booster, it was supposed to be for all 2015-2018 Silverados and Sierras at no charge as far as I was aware. It is Special Coverage N182202780 and is covered under this special warranty for 10 years/ 150,000 miles.