Mass Air Flow Sensor or O2 Sensors Needed?

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Bob Markey 2

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I have had issues with the "check engine" light for months. I replaced a few things, such as plugs, wires, etc., but now I am getting two error codes (P0172 and P0175), which the auto parts store guy says is most likely the mass air flow sensor.



Before I go out and by this $80 to $150 part, I am concerned it could also be the O2 sensors, which the codes list as secondary causes.



The vehicle is a 2005 V6 ST with Flex fuel engine and 133,000 miles.



I would appreciate advice as to how to proceed - especially from those of you who have been through this - and any tips on the least expensive ways to get the sensors.
 
I think you're going to need a scan tool to diagnose your issue. Also check out videos at ericthecarguy.com. Let us know what you find.
 
Vic is right, you are going to need a scan tool on this one. It is highly unlikely that both of the O2 sensors went bad at the same time. The Maf could be the culprit, perhaps try cleaning it first.
 
Thanks. I bought some canned spray cleaner for the MAF sensor a few months ago. Maybe I'll try it again.



I'd hate to buy a $90 MAF sensor and then find it it's something else. The scan tool at the auto parts store only gave likely culprits, with the MAS sensor being at the top of the list.



Am I doing any damage driving it like this?
 
It is most likely not your O2 sensors. They are what is sending the code. It may be the MAF... The vehicle has a lot of miles on it too. My experience says to check the TPS. It could be going bad and giving too high of voltage reference. Check it with an analogy volt meter. Using the ohm testing side check the voltage reference wire with key on engine off. Open and close the throttle and watch the sweep. If it jumps around it is a bad one. They have a tendency to wear out where the throttle position gets worked the most... Also a good cleaning to the MAF is most likely in need.
 
I BET its the dam vaccume elbow...... >75 cent part !



Todd Z
 
People he has codes p0172 and p0175, these are rich codes not lean codes which means that any vacuum leaks are out of the question as a possible problem.



Like I said earlier both O2 sensors going bad at the same time is HIGHLY unlikely. Typically when an O2 sensor throws a rich or a lean code it is also accompanied by a code for a stuck O2 sensor.



Using the scan tool to diagnose this is more than just pulling codes, which is all the parts store is capable of doing. One will need to look at the pcm data to see what exactly is going on and maybe even some physical testing to verify some of the sensors and wiring.



Driving like this can damage the catalytic converters not to mention the decrease in mpg. I would suggest finding a local mechanic that you can trust and have them diagnose it. Once they diagnose it let us know what they come up with and I can tell you if they are being honest with you.



For future reference NEVER use an analog meter to test ANY circuit on a vehicle with a computer unless you designed the system and know exactly what you are testing. You just may end up frying a computer and adding to your problem and lightening your wallet considerably.
 
Go out on Ebay and buy a chip to plug in to the data link. Down load the app to use it as your own scan tool through your phone. you can see the system operation in driving mode. watch the O2 sensors change and MAF TPS Fuel Pressure... you name it. Costs around 40 bucks I think and will save you tons in guesswork changing parts.



I would clean the MAF and clear codes then take back to Zone or wherever it was scanned and see if it changed. it picked up a code for some reason! ignoring it is like seeing a big buck in the woods and going the other way because you think its grandad might be the other direction.:eek:fftopic:
 
Oh Jeeez, an analog voltmeter will not and can not short out an ECU. Particularly in an ohm measurement mode. The TPS is a simple pentiometer. Hence, voltage in ( 5 volts ), a reference wire usually right below or at 1 volt @ idle ( key on engine off ). And a ground wire. Once probed to figure out which wire is which. It can be tested disconnected and key off. It is a simple resistance test across the voltage reference circuit. If the gauge sweeps smoothly it is fine when throttle is moved ( in our case the TPS would have to be removed to simulate throttle movement ). This is something that can't be analized on a digital meter or watching a scope and activating the throttle... I have done this dozens of times on my SVO, Cobra, Ranger and Explorer.
 
Calahan,

I use an anolog. To bench a TPS also. I will use a digital to set the base dcv,koeo. Or to check the WOT dcv, koeo.

There are few other reasons, to have an anolog around also...

Im a retired Instrument tech. We still kept a couple of old big simpsons around.
 
Like I said, if you know the circuit you are testing then all is well with using an analog however if you don't know then don't do it. Especially don't just start probing wires to figure out which is which. I have seen more than one person wipe out a computer driver by testing with an analog meter. As far as ohms testing goes I find it a useless test unless you are looking for an open or shorted circuit. Testing a circuit while it is at rest is about as useless as putting air in a tire with a huge hole in it.
 

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