The fluid being low is an indicator for worn brake linings, usually the pads, but maybe shoes.

 

donbrew, that could be as far as front pads are concerned.
Wheel cylinders on the rear brakes will/should return to a fully closed positon when the brakes are released. Therefore, a low brake fluid level would not be a indicator of worn rear shoes.
I would think the OP has worn pads or a leak that he hasn't noticed.
Back in the day, I recall a few master cylinder jobs where they would leak back into the vacuum booster. Never showed a visible leak, but the customer was losing a small amount of fluid.

 

Well little update : Just added about 5 to 6 ounces dot 3 when car sat all night about 40 degrees and started it took off went a couple of blocks no light have a good pedal and good stopping power .... I mean i never did anything with the brake fluid in 6 years shame on me i know ,should i replace all the fluid and bleed the system ? or leave it alone and don't fix it if is not broken

 

Two trains of thought there...

1. Let sleeping dogs lie and assume everything is OK now that it's topped up.

2. Flush the system out, refill with new fluid, and bleed it.

I'm inclined to go with #2.

Brake fluid is hygroscopic which means that it attracts moisture, and most vehicle manufacturers recommended changing it out every two to five years. That removes not only the old contaminated fluid, but it cleans out any loose particulate matter generated by corrosion in the system.

 

Brake fluid does not evaporate. It goes somewhere, either into the cylinders or onto the ground.

I still have not seen any mention of checking the wear on the pads. That is the first, most important thing to do!!! Then worry about topping off the fluid. Last year I had a set of pads wear down almost to metal in 20,000 miles I was assUmeing they would go for at least 40,000 so I was not checking them as I normally do.

I am assuming that when the pads were changed last somebody cared enough to look at the fluid level.

If it took 5 or 6 ounces of fluid, you are lucky to still be alive. Brakes are sort of important.

Yes, George that is why the "maybe" qualifier was there. Could have broken return springs and/or adjusted all the way out. You just can't tell if nobody has inspected anything because "I just had the brakes done a year or 2 ago". How many miles is that, have the rears been monitored/adjusted (ever)?

 

well going to have the rears checked they maybe not be adjusted right like you mention and have the fluid flushed thanks

 

My brake fluid warning comes on at startup if the car sits for any length of time in below zero weather but it goes out in a few minutes.

 

I seem to remember a TSB for that.

 

https://www.chevyhhr.net/forums/showthread.php?p=443904 post #129

I LOVE that new SEARCH tool

 

I see this thread is years old, but this seems to be a new problem for me. I own a 2009 HHR and it has just over 80K miles. Just this week I have brake fluid and traction error lights. It has been sub zero temps so I was thinking it was because of the cold weather. I have never had these errors. I talked to some guy at Monro and he said it's a brake issue. I had them done with lifetie warranty and now he supposedly can not find the job in his computer. Should I just top off my fluid? Monro will not.