Would a Vacuum Leak at the HVAC Controls Cause a P0101?
 

I bought a 2003 Blazer around 2 1/2 weeks ago, and before even getting a chance to register it the SES light came on and it was a P0101 code. I cleaned the MAF, but a day later the code came back. Since the truck would obviously not pass emissions with the SES light on, I took it back to the dealer. They replaced the MAF sensor for free and the light didn't come back on, until today. Same P0101 code. Obviously they didn't diagnose and repair it correctly. Later on today I'm going to call them and see if they'll fix it right. In the meantime, I figured I'd try to find out what the problem is for myself. I think that there is a vacuum leak at the HVAC control. There is a hissing noise coming from the dashboard that stops when you put the vent selector knob to off. From reading here I know that a vacuum leak can cause this code, since the amount of air that is entering the intake doesn't match what the MAF sensor is reading. Would a leak that far from the intake cause this code? Thanks.

Doubtful. Vacuum leaks are extremely common in these vehicles and we rarely see them coupled with SES codes.

Follow the steps in this flow chart exactly as written, and it will take you right to the problem. https://blazerforum.com/forum/diagno...plained-31561/

Thanks for the reply. Looks like I'll have to dig a little deeper to get to the bottom of this. The SES light is off now, so it seems that this code is intermittent. I haven't noticed any drivability issues yet, so I guess it's not a pressing issue, but eventually I'd like to figure this out.

Edit: Thanks Captain, I started to follow the chart the first time the light came on (before the shop replaced the MAF). I'll redo it again. I was just trying to see if the HVAC leak was related to this issue.

Like aa mentioned, it's doubtful, but not impossible. Follow the flow chart, it's straight out of the GM factory shop manual, don't skip any steps, you'll find the problem.