01 Yukon noise when braking or downhill

[Coastalyetti]

New to the forum, any insight appreciated. I have a 2001 Yukon 4x4 with 168k. After some hard driving to a job site in the mountains truck started making a low pitch hiss when braking, kinda like a dryer vent sounds like outside the house. Brakes were pretty worn so replaced pads, rotors and park brake shoes. Still makes noise. Calipers seem fine no leaks or corrosion, lines and fluid seem good, axle seals dry, parking brake works and pedal feels normal. Then I noticed a very similar or same noise when it was parked downhill at idle. Could it be the same issue??Can’t tell where it’s coming from, engine bay or underneath. Truck leaks oil from valve covers and somewhere else lower. I had a shop replace the air pump and check valves, pump was full of water and died, to pass Ca smog two years ago. I can’t tell if it’s getting louder or I’m getting more irratated with it. Oh and the abs and park brake lights started coming on randomly, gotta love it. Where should I start????

 

[MassHoe04]

If the lights are coming on, but not staying on, there still must be stored codes somewhere in the system. See what a decent scanner can tell you.

Tech 2 scanner can go deep into almost every component to check what they are doing or not doing. If you don't have access to a Tech 2, you may be able to see codes stored with a decent scan tool.

My Zurich from Harbor Freight allowed me to get in to see codes that were were not active, but were stored. That information was in a special sub menu called "GM OEM Enhanced" (or something like that... But, they were there. My ABS light would come on only on the highway, then go off around town. I was able to see stored codes indicating left front ABS speed sensor output. That helped a lot!

 

[Joseph Garcia]

Welcome to the Forum from NH.

Lots of knowledgeable folks here who freely share their knowledge, experiences, and perspectives. Knowledge is power.

I hope that you will become a participating member in the Forum's discussions.

Pics of the truck, please.

I cannot personally help you with your question; however, other members on this Forum that are much more knowledgeable than me will chime in.

 

[Coastalyetti]

If the lights are coming on, but not staying on, there still must be stored codes somewhere in the system. See what a decent scanner can tell you.

Tech 2 scanner can go deep into almost every component to check what they are doing or not doing. If you don't have access to a Tech 2, you may be able to see codes stored with a decent scan tool.

My Zurich from Harbor Freight allowed me to get in to see codes that were were not active, but were stored. That information was in a special sub menu called "GM OEM Enhanced" (or something like that... But, they were there. My ABS light would come on only on the highway, then go off around town. I was able to see stored codes indicating left front ABS speed sensor output. That helped a lot!

Definitely considering investing in a scan tool, shop rates around here are getting $$$

 

[MassHoe04]

Definitely considering investing in a scan tool, shop rates around here are getting $$$

Before I got my Tech 2, I got the middle of the road (the one for $129) Zurich from HF. The one that dealt with ABS and airbags. Was not terribly expensive and still use it today. I used it last night to check alternator and battery on mine. I am still earning my way around the Tech 2 and I knew how to do the two tests on the Zurich already. I actually keep it in my center console all the time, in case a code comes up on the road. I can see if it the pesky EVAP code I get or something more urgent.

Tech 2 is about $300 for new clone, but they can dive so much deeper into specific modules and what they are doing. You can turn things on/off and see what in/out voltages are, etc. As I learn more about it, I will be able to do much more. I did use my Tech 2 a couple of months ago. I was able to rule out battery, ignition and park.neutral switch as the cause of my no crank/no start before AAA even showed up with the flatbed... Ran to get the new starter and was back in business in a few hours.