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Matt
Matt, Engineer
Category: GMC
Satisfied Customers: 21990
Experience:  Honors degree in Mechanical Engineering, worked 8 years as a Formula 1 engine engineer.
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P0101 code and reduced Engine power flashes, P0101 mass air

Customer Question

P0101 code and reduced Engine power flashes
JA: Just to clarify, what's the exact code? And have you tried to reset it?
Customer: P0101 mass air flow sensor and yes I have rest it with a scanner
JA: What is the model/year of your GM?
Customer: 2009 GMC Sierra 2500HD duramax
JA: Are you fixing your Sierra 2500HD yourself? What have you tried so far?
Customer: yes, replaced MAF Sensor, Cleaned Sensor,
JA: Anything else you want the mechanic to know before I connect you?
Customer: I have Cold Air Intake, Banks Monster exhaust, and just installed new MAF Sensor.
Submitted: 2 months ago.
Category: GMC
Expert:  Matt replied 2 months ago.

Hello

to get the P0101 code -(Mass Air Flow Sensor Circuit Range/Performance). then there's something up with the MAF or there's a vacuum leak or something in front of the MAF thats disrupting the airflow

as the code is is set when the signal from the mass air flow sensor is out of expected range

I suspect that the MAF sensor may being disrupted by the aftermarket cold air intake, especially if the MAF sensor has been relocated from the stock position so it may be worthwhile to put that part back to stock to see how this helps

also check for vacuum leaks after the airflow meter, any air dragged in here isn't 'seen' by the ECU and so not compensated for and can lean the engine out and can also allow the engine to rev up when not desired causing rough running.

As its a mechanical fault it tends not to turn on the fault light and you can sometimes hear a 'hissing' noise with the engine running.

Check the hose clips for tightness and inspect the trunking for any cracks or splits and also all the vacuum system, the small bore pipes and fittings for cracks and missing parts.

The best way to locate a leak is to have the engine running and warm and then spray lighter gas /propane or brake cleaner around each joint in turn. If the engine rev's up you've found your leak.
Now you might think that spraying lighter gas around a hot engine isn’t wise, however the flash /ignition point of gas is about 400°C so you need a naked flame or spark to set it off and I’ve used this method for many years without incident.
Work your way through each possible joint one at a time and you should find it. I use a slightly flattened piece of brake pipe and some rubber hose from the can of lighter gas to provide a spraying 'wand' and allow a direct blast of gas into each area, especially those difficult to reach with large implements.

Air leaks are very temperature dependent as gaps can open up as things expand with temperature so depending on how the leak occurs ( on a hose joint with a clamp expansion will help seal and on a vacuum hose expansion ill make a leak worse) so leaks can be better or worse as the engine heats up.

Customer: replied 2 months ago.
Great I will look into those. I have had the cold intake on for quite a while without issue and am thinking it might be a air leak. does the lighter gas work on a diesel engine as well?
Expert:  Matt replied 2 months ago.

Hello Yes

lighter gas or brake cleaner will work on a diesel just fine