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Discussion Starter · #1 ·
Hey guys
I have a volvo s40 2005 2.4i (not turbocharged)
And from last few weeks it has been giving me a engine light so i plugged an obd2 scanner and got the code p0172.
My car does have a mototec air intake installed and pretty sure there are no air leaks. i dont want to spend like 300 bucks on a new o2 sensor and find out the engine light is for another reason. Anyway i can definitely find out the reason for my engine light? What other possible reasons could it be for the engine light?

Thanks
 

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Well, that's a bit of an odd one. Mixture too rich. Not an O2 sensor issue.

If you are using an oiled air filter clean the MAF. Even if you aren't it can't hurt as a first step. Filter clean?
Could be the precursor to a failed fuel pressure sensor also. Running fine?

Check those & get back to us.
 

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Hey guys
I have a volvo s40 2005 2.4i (not turbocharged)
And from last few weeks it has been giving me a engine light so i plugged an obd2 scanner and got the code p0172.
My car does have a mototec air intake installed and pretty sure there are no air leaks. i dont want to spend like 300 bucks on a new o2 sensor and find out the engine light is for another reason. Anyway i can definitely find out the reason for my engine light? What other possible reasons could it be for the engine light?

Thanks
Since your car is not turbocharged, air leaks (or in this case a vacuum leak somewhere along the air intake) would not cause a mixture too rich condition. Since a naturally aspirated engine relies on lower pressure from the air filter to the throttle body, if anything, an air leak in this system would cause a mixture too lean condition since the engine would be pulling in more air than it expected after the MAF Sensor.

A mixture rich condition means something is happening that is dumping more fuel into mixture than is needed. I would start with your MAF sensor. Disconnect it, clean it with MAF cleaner liberally, and electric connector cleaner at the connector and then blow it out gently or let the fluid in there evaporate. There are those that believe the self-heating wire takes care of everything if your model has one, I really never believed a lot of that stuff. I believe it helps, but it is not a cureall because if you heat up organic material and it has an attractive charge. Be gentle with everything you do with that sensor, and if you break it, it's not my fault. If this works, it means your MAF was dirty, and reporting different numbers to the engine despite what was actually going by it. It also might mean your MAF is bad if it's reporting bad numbers to the computer. If it is reporting bad numbers, it'll mean your computer has tried to reduce the fuel trim the maximum amount but it still "thinks" it's putting too much fuel in with the air.

Next step in the system is the throttle body and injectors. If the injectors are not opening and closing correctly with their pulses and dumping more fuel into the system than they should be. Your throttle body as well, may not be opening allowing enough air to enter the system when commanded to do so by the computer(might be dirty or sticking). Disregarding a defective sensor in your exhaust, this are the only systems involved besides the computer itself that could give you a mixture too rich code.
 

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Discussion Starter · #4 ·
Alright I am going to try to clean the MAF thoroughly and then will get back. If the engine light still keeps coming do I just open the throttle body and injectors and clean it up? Also My mechanic keeps suggesting to replace the o2 sensor. Should I listen to him and spend like $300 or will it be useless right now?
Thanks
 

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An O2 sensor at this point is useless.
Clean MAF with directions on can.
Run some injector cleaner through the fuel system. A full can of Seafoam in a full tank of fuel will do the trick.
You can clean the throttle body if you wish. Very doubtful it will have any effect unless it's so filthy it's sticking.
 

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Grab a fuel pressure gauge to measure it at the rail. If that is good, then it's probably something to do air (MAF or vacuum). But rule out as much as you can first. Plus fuel pressure is easy to check.
 

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Grab a fuel pressure gauge to measure it at the rail. If that is good, then it's probably something to do air (MAF or vacuum). But rule out as much as you can first. Plus fuel pressure is easy to check.
+1 Good point. If it is the start of a fuel pressure sensor failure this will help you pin it down. Most likely you will also throw a code for that sensor as more time passes.
 
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