Sensor issue caused by worn head gasket?

[CraigLloyd]

Hey everyone. My wife has a 2007 Vibe and her check engine light came on the other day. We took it to a mechanic in town to get it looked at, expecting it to be just something simple. It turns out that a sensor telling the car how much fuel vs. air the engine is supposed to take in is malfunctioning (I'm guessing it's the mass airflow sensor, but my wife forgot the name of it exactly).

The mechanic said he'd charge $150 to replace it -- that's cool with us. BUT, he also said the head gaskets were worn out and that's what caused the sensor to act funny, so another $750 added on to that -- AWESOME. Does this seem logical? I'm no mechanic and don't know A LOT about engines, but I wanted to be sure he's not trying to rip us off by making up a weird story. He seems to have a good reputation and we were actually referred to him by friends, but I've been conditioned all my life to have caution around mechanics.

Of course, I may just subconsciously be upset that we're going to have to spend $900 on a surprise repair, but let me know what you think.

[circuitsmith]

Head gaskets don't wear, they leak. Get a second opinion, and maybe another mechanic.
Symptoms of a bad head gasket include overheating, loss of coolant, white smoke from the exhaust, rough engine running & misfire.
Did the mechanic tell you what the error code was? It's a "p" then 4 numbers, like p0123
Those error codes don't say directly what part is bad.
Further checking should be done to confirm a part is bad.

[Raven]

MAF sensors rarely fail. It may be dirty though. It is easily cleaned with electrical parts cleaner spray or even brake cleaner. Something that does not leave a residue.
A new Denso 197-6030 MAF is about $75.00 and 15 minutes to change it.
The other possible sensor would be the oxygen sensor. The first sensor in the exhaust system is now sometimes called the air/fuel sensor. It checks if the engine is running rich or lean. It could have failed if you are getting up there in mileage. $150.00 to change it is a decent deal. They are a PITA to remove.

If he said the head gasket is worn out he is likely a scammer. As said they leak, they don't wear out. Head gasket failures are extremely rare on Vibes.

I would not trust this guy at all. Go to another garage.

P.S. Is the code # PO171 by any chance?

[Salsa Guy]

Before changing ANYTHING post the Code from the car. Take is to a local Auto Parts store and they will do it for free. I think it's a P0171 and it that's the case it could have a bad intake manifold gasket, change the O2 sensor or MAF WILL NOT normally fix it. Which is a simple very cheap repair. The parts are less than $20 and it should be only 1 hour of labor. So less than $150 on the high end.

This guy is taking you for a ride. Head Gaskets are not normally an issue on these engines, but Intake Manifold Gaskets can be.

[CraigLloyd]

Thanks, guys. I'll call him back to find out the code, but I'll take it to an auto parts store anyway to get the code from a third party. I'll report back once I find out more.

[Raven]

Before changing ANYTHING post the Code from the car. Take is to a local Auto Parts store and they will do it for free. I think it's a P0171 and it that's the case it could have a bad intake manifold gasket, change the O2 sensor or MAF WILL NOT normally fix it. Which is a simple very cheap repair. The parts are less than $20 and it should be only 1 hour of labor. So less than $150 on the high end.

This guy is taking you for a ride. Head Gaskets are not normally an issue on these engines, but Intake Manifold Gaskets can be.

I see you read my clue Dr. Watson.

[CraigLloyd]

Ok, so my wife tells me the check engine left turned off after her trip to the mechanic, but we went ahead and went to get a second opinion and see if they could still pull a code off of it, and they said that the entire code history was erased, so we have to wait until the light turns on again.

Either way, the car still runs fine and we haven't noticed any changes in performance, so I think we can afford to wait a little bit.

[Raven]

It's not a major issue. It may or may not come back on. He probably erased the code so you couldn't prove the scam he was trying to pull.

[Salsa Guy]

Before changing ANYTHING post the Code from the car. Take is to a local Auto Parts store and they will do it for free. I think it's a P0171 and it that's the case it could have a bad intake manifold gasket, change the O2 sensor or MAF WILL NOT normally fix it. Which is a simple very cheap repair. The parts are less than $20 and it should be only 1 hour of labor. So less than $150 on the high end.

This guy is taking you for a ride. Head Gaskets are not normally an issue on these engines, but Intake Manifold Gaskets can be.

I see you read my clue Dr. Watson.

I just glanced over your reply and would never suggest cleaning the MAF. LOL Cleaning the MAF you can do more harm than good, it's somewhat a tender device. But the rest of your post was spot on after re-reading.

OP Yes a P0171 is a lean code, which can be dangerous to the engine and should not be ignored. If the head gasket is failing you would have some other major issues. Just for your own piece of mind check the coolant level and color. If it's milky and foamy that's a bad sign. Also check the engine oil level and color. If it's milky brown that also is a bad sign. Both point to a bad head gasket.

[Raven]

[/quote]

I just glanced over your reply and would never suggest cleaning the MAF. LOL Cleaning the MAF you can do more harm than good, it's somewhat a tender device. [/quote]

I have cleaned the MAF sensor on dozens of vehicles with excellent results. It is important not to touch the guts, just spray it clean lightly. I even opened them up and resoldered the contacts inside on two of the three Subaru SVX that I own.

[Salsa Guy]

It sounds like you have been lucky my friend.

[lannvouivre]

I even opened them up and resoldered the contacts inside on two of the three Subaru SVX that I own.

Jeebus, how'd they come loose? Sounds like a big design flaw to happen a majority of the time.

I have cleaned my MAF sensor a few times with the MAF sensor cleaner spray. It's very dusty down here, so it doesn't take long for it to look like I live in west TX or something. What would cause it to be damaged, if you never touch the glass temp bulb or the air flow wire (or drop it)? I realize it's comparatively delicate to most parts.

[Raven]

I even opened them up and resoldered the contacts inside on two of the three Subaru SVX that I own.

Jeebus, how'd they come loose? Sounds like a big design flaw to happen a majority of the time.

I have cleaned my MAF sensor a few times with the MAF sensor cleaner spray. It's very dusty down here, so it doesn't take long for it to look like I live in west TX or something. What would cause it to be damaged, if you never touch the glass temp bulb or the air flow wire (or drop it)? I realize it's comparatively delicate to most parts.

Yes it was problem with the early SVX. My '97 has been fine. The major transmission problem sent a lot of them to an early grave.

[CraigLloyd]

An update! I spoke to the original mechanic myself and got a confirmation on what was wrong with it (previously I was getting the info through my wife). He says the check engine light was on because the mass airflow sensor was malfunctioning and needed replaced. He also discovered that the intake manifold gasket was leaking and needed replaced. He said all of this would cost about $600 total.

Are there symptoms of a leaking intake manifold gasket that I could look for? I'm told decreased gas mileage is one of them. In any case, we're gonna wait for the check engine light to come back on and take it somewhere else for a second opinion.

[Raven]

More than likely it's just the intake manifold gasket.

[CraigLloyd]

More than likely it's just the intake manifold gasket.

So you think the MAF sensor is ok?

The car is running fine and I've been reading that a symptom of a leaking intake manifold gasket is rough idling and mis-firing, but we haven't experienced any of that.

[Raven]

The MAF should be fine. In my experience (since they started using MAFs) when a MAF is bad, the car runs poorly or not at all.

If the intake manifold gasket is bad there may be no symptoms at all, like on my '06 Vibe.

If the CEL comes on again, please get the code#. That will be a determining factor.

[SeattleJeremy]

I agree with Raven, replace the intake manifold gasket first.

Here is what I suspect is going on.
The MAF sensor figures out how much air is coming in to the engine. This sensor is located just after the air filter.
The failing intake manifold gasket is letting un-metered air in to the manifold.
Then in the combustion chamber the air : fuel ratio is wrong (or lean) because of the un-metered air. The Oxygen sensor, located on the exhaust manifold, detects the lean condition, and the computer (ECU) does math to figure out where the problem is coming from. Since there is too much air, it thinks the MAF isn't doing it's job correctly.

Hope that helps