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Check Engine Light On Again? Any Car Experts?

Old 06-09-2019, 02:12 PM
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Default Check Engine Light On Again? Any Car Experts?

I have a 2007 Chevy Trailblazer and just passed 60k and changed the air filter and a code popped up indicating Mass Air Filter sensor was needing replacement. I replaced it and maybe 2 days later light comes on again, this time code P0172. This is supposedly a very common code and P0172 is Fuel System Rich Bank 1 and is thrown when the oxygen sensors detect that the air fuel mixture is too rich. Bank 1 refers to the rich condition being detected on the side of the engine with cylinder 1. At the same time I wanted to change the oil so took it in to Pep Boys, they did the oil and confirmed the code was P0172. I added a can of Berryman B-12 and the code went off a few hours later. Drove the car to airport which is about 85 miles and on the return trip almost home the light came back on, strange. The car starts and runs fine although my car battery died the day after I had my oil changed so replaced it but no fuel smell or other issues. I did take it in to Firestone but they are not able to work on it but gave me a printout of potential issues. It did go off yesterday afternoon but returned a few hours later, I am assuming it is the same code but really need to check it again. I really have no idea what the issue is and frankly do not want to take it to the dealer, at least not yet. Any words of wisdom? I most likely will take it to them if it does not go away after my current tank of gas is used up. Thanks for any advice.
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Old 06-09-2019, 02:16 PM
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Time for you take her to a shop. Not Pep Boys or Firestone, but a real shop.
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Old 06-09-2019, 02:29 PM
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Bad oxygen sensor is my first guess. Second guess would be fuel pressure regulator.
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Old 06-09-2019, 02:35 PM
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Google is your friend. Ask him
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Old 06-09-2019, 02:36 PM
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You don't by any chance have an oiled air filter like K&N, do you? Also, check for leaks on the intake area, like cracks or hoses that are disconnected. Might be a small vacuum leak.
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Old 06-09-2019, 02:48 PM
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Do these symptoms sound familiar? This was fixed by replacing a fuel pressure regulator.
How do I find the cause of P0172 (Rich bank 1)? - Car Forums and Automotive Chat
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Old 06-09-2019, 03:13 PM
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Originally Posted by SOSC View Post
You don't by any chance have an oiled air filter like K&N, do you? Also, check for leaks on the intake area, like cracks or hoses that are disconnected. Might be a small vacuum leak.
Definitely not a vacuum leak. A vacuum leak would add air to the fuel/air mixture and cause a lean condition. The op is getying excess fuel, causing it to run rich.

Op, you really have a myriad of issues (from a bad 02 sensor to a bad fuel injector to a bad reference signal to a bad maf sensor, etc), without graphing your fuel trims, anything is just guessing.
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Old 06-09-2019, 03:18 PM
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Originally Posted by Jersus View Post


Definitely not a vacuum leak. A vacuum leak would add air to the fuel/air mixture and cause a lean condition. The op is getying excess fuel, causing it to run rich.

Op, you really have a myriad of issues (from a bad 02 sensor to a bad fuel injector to a bad reference signal to a bad maf sensor, etc), without graphing your fuel trims, anything is just guessing.

And this is what the ECM does in this case when it detects a lean condition. One of it's primary functions is fuel management. A vacuum leak fools ECM into thinking there is a lean condition therefore it adjusts to a rich "solution"..
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Old 06-09-2019, 03:23 PM
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Looks like o2 sensor time
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Old 06-09-2019, 03:32 PM
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Originally Posted by SeekingStripers View Post
I have a 2007 Chevy Trailblazer and just passed 60k and changed the air filter and a code popped up indicating Mass Air Filter sensor was needing replacement. I replaced it and maybe 2 days later light comes on again, this time code P0172. This is supposedly a very common code and P0172 is Fuel System Rich Bank 1 and is thrown when the oxygen sensors detect that the air fuel mixture is too rich. Bank 1 refers to the rich condition being detected on the side of the engine with cylinder 1. At the same time I wanted to change the oil so took it in to Pep Boys, they did the oil and confirmed the code was P0172. I added a can of Berryman B-12 and the code went off a few hours later. Drove the car to airport which is about 85 miles and on the return trip almost home the light came back on, strange. The car starts and runs fine although my car battery died the day after I had my oil changed so replaced it but no fuel smell or other issues. I did take it in to Firestone but they are not able to work on it but gave me a printout of potential issues. It did go off yesterday afternoon but returned a few hours later, I am assuming it is the same code but really need to check it again. I really have no idea what the issue is and frankly do not want to take it to the dealer, at least not yet. Any words of wisdom? I most likely will take it to them if it does not go away after my current tank of gas is used up. Thanks for any advice.

Dealer would be the absolute last place I would take it to - unless I was broke down in Death Valley on the hotest day on record. These emission issues at the dealer can become an open check book feast if you are not careful.

If your going to keep the truck for any length of time and you are handy diagnosing and fixing things invest in Tech II Tool off eBay - knockoff version and the DVD manual from the factory. Those 2 aids have saved me thousands in repairs.
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Old 06-09-2019, 03:33 PM
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Stop stop stop!!!
What brand of MAF did you replace it with?
What oil filter did they use?
What scanner was used to reset properly??
Let's stop...figure shit out before complicating the problem more...1 action can cause another...call me if you'd like
14013006548
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Old 06-09-2019, 03:45 PM
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Originally Posted by magua View Post
And this is what the ECM does in this case when it detects a lean condition. One of it's primary functions is fuel management. A vacuum leak fools ECM into thinking there is a lean condition therefore it adjusts to a rich "solution"..
It does not fool the ecm. The lean code will trigger before the false positive rich code.
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Old 06-09-2019, 03:48 PM
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What engine do you have, 5.3L ? If so the oil pressure switch is notorious for going bad. I had to replace mine 2 times. You can get to it by climbing up and blindly reaching it. It is on the drivers side right by the firewall.

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Old 06-09-2019, 03:56 PM
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There is a chronic and well known wiring issue with the plug that plugs into the throttle body. It's a possibility. Throws all kinds of crazy codes.
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Old 06-09-2019, 04:13 PM
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You didn't have p0172 until you replaced the MAF sensor so that's where I'd turn my attention to. Aftermarket mass air flow sensors can be dodgy. They'll really mess you up because you don't believe the new part is causing your problem so you load the ole parts cannon.
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Old 06-09-2019, 04:50 PM
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Great advice from everyone, thanks for all the tips. I do not use a K/N oil filter. The engine is the 6 cylinder 4.2 Liter. The oil change used Mobil 1 Oil and a Puro Tech oil filter. I am not sure what brand scanner was used to check for the codes. I did replace the failed MAF with a Car Quest brand MAF sensor about 2 weeks ago and I think I am going to take the suggestion by Elgreco809 and replace the MAF sensor with another brand tomorrow and see what happens. The code has come and gone a few times and I realize it could be a number of issues. The car starts, runs and accelerates fine. Thanks again for all of the great suggestions, keep hoping it goes away and does not return.
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Old 06-09-2019, 05:18 PM
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Originally Posted by SeekingStripers View Post
I have a 2007 Chevy Trailblazer and just passed 60k and changed the air filter and a code popped up indicating Mass Air Filter sensor was needing replacement. I replaced it and maybe 2 days later light comes on again, this time code P0172. This is supposedly a very common code and P0172 is Fuel System Rich Bank 1 and is thrown when the oxygen sensors detect that the air fuel mixture is too rich. Bank 1 refers to the rich condition being detected on the side of the engine with cylinder 1. At the same time I wanted to change the oil so took it in to Pep Boys, they did the oil and confirmed the code was P0172. I added a can of Berryman B-12 and the code went off a few hours later. Drove the car to airport which is about 85 miles and on the return trip almost home the light came back on, strange. The car starts and runs fine although my car battery died the day after I had my oil changed so replaced it but no fuel smell or other issues. I did take it in to Firestone but they are not able to work on it but gave me a printout of potential issues. It did go off yesterday afternoon but returned a few hours later, I am assuming it is the same code but really need to check it again. I really have no idea what the issue is and frankly do not want to take it to the dealer, at least not yet. Any words of wisdom? I most likely will take it to them if it does not go away after my current tank of gas is used up. Thanks for any advice.
no such thing as a Mass Air Filter sensor

usually the 1st thing you do when the Mass Air Flow sensor code shows up is clean it.

you replaced the air filter and there is a good chance you got crud on the sensor.

clean the one you pulled out and put it back in to see if that helps

if the ECU does not know the proper amount of air rolling in how can it adjust the proper amount of fuel?

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Old 06-09-2019, 05:45 PM
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I'll retract my suggestion because Jersus is correct. A vacuum leak or dirty MAF would normally cause a lean code to be set before going into open loop.

The only time I've had a rich mixture code was also when I had a misfire code at cold idle, and that was due to carbon build up on an injector and in the cylinder. But that was a turbocharged direct injection engine, not port injected N/A'd. As suggested, the sensors seem to be the culprit, but it's hard to tell which. The long term fuel trims would tell you whether the injectors are being held open longer than normal. I would start with replacing the MAF and bank-1 O2 sensors, then go from there. MAF since it's likely cheaper and easier to replace, like you said.
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Old 06-09-2019, 05:48 PM
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Sorry, I typed too quickly...Mass Air Flow Sensor...you are correct 99yam40. Thanks for the advice, I am ordering an AC Delco OEM MAF sensor and installing that this week. Hopefully this will clear the code.
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Old 06-09-2019, 08:08 PM
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I would get a scantool that displays real time OBD2 engine data. They are not expensive. I have one that cost $20. You can then see the amount of fuel trim being set on each side. It may be that one side is way off and the other is fine, or it could be that both are way off and only one is out of range and setting the code so far. Both off may indicate a MAF failure. One off only is usually an O2 sensor or a stuck/leaky injector. This particular scantool reads the engine data as well as the codes.

https://www.ebay.com/i/401766467475?chn=ps

Last edited by GaryDoug; 06-09-2019 at 08:13 PM.
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