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MAF sensor, throttle, catalytic converters

Hi there!

I have a Volvo S60 (turbo) from 2005. She almost all the time had an engine light on (I bought it this way), but was told it might be just a sensor. Mechanics would reset it when I had to get it inspected.

  1. Took the car to the mechanic to get it checked for maintenance. He changed the air filter and added some oil. He also found some codes such as 140C, 140D, 120D, and 400C. Told me there might be something about the catalytic converters but that is too soon to tell.
  2. A few days later the maintenance message came to my dashboard. The mechanic changed the oil, oil filter.
  3. Next day I drove the car many miles. Then the day after the dashboard said “reduced engine performance” and stopped running (in idle).
  4. He told me the throttle body needs to be replaced. We replaced it and was told to bring it back if the engine light comes back. It did.
  5. Took it to AutoZone to read the engine light and they said it is a code for the catalytic converter. I just needed to double-check.
  6. Went back to my mechanic and he told me to buy this special additive to add to the fuel tank to “clean” the converters. He took out the engine light to see if it comes back after I drive it with this additive inside the fuel tank.
  7. Engine light came back on and the codes were air mass flow and catalytic converter. This back and forth happened twice as he said that it takes a few rounds to diagnose a problem on the Volvo.
  8. Today he told me to change the air mass flow.

I am a female so my car mechanics knowledge is limited, hence, that’s why I am here.
Is there a connection between air mass flow and a catalytic converter? What about the throttle body in connection to the catalytic converter? What other options do I have to make sure it is not the catalytic converter? What other tests can he do on her to rule out the converter? Has this happened to your Volvo? Please share.

Thanks for your help and advice.

No need to feel bad because you have limited vehicle knowledge . Many people male and female are just like you . From your post I don’t think you have a good mechanic looking at this . Him saying an additive will clean your Catalytic Converter is wrong. Use the online sites for your area , friends , relatives and coworkers to find a different shop. You might even do a web search for European vehicles shops or a Volvo dealer ( which will not be cheap ).


I just flagged your post because it looks like spam. There are no miracle cat cleaners in existence. Please remove the link.

If you are getting a code for throttle body followed by a code for the mass air flow (MAF), you may well have a serious problem with the catalyst. Has this car historically burned a lot of oil? When oil burns, it leave behind ash which collects in the catalyst and plugs it up, and there is no magic cleaner that I know of that will remove that ash.

If the catalyst plugs up, the computer will be confused because the air flow reported by the MAF will be too low relative to the throttle opening reported by the throttle body and the engine RPM. A competent mechanic will spot this problem quickly by measuring the vacuum at fast idle or by removing the top oxygen sensor and measuring the pressure in the exhaust manifold.

Another possible cause of confusing air flow readings is cracks in the tubing between the MAF and the engine. However, the mechanic who replaced the throttle body would have seen any cracks in the plastic tubing.

I’m sorry if you didn’t mean it as spam. It is unfortunately common for a first timer/spammer to post a reasonable question, then follow it up with a second post containing link to some snake oil solution. You did just that.

There is no problem saying you added an additive. But posting the link is the problem, to me.

The more you protest, the more I wonder…

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Well that escalated quickly…


@cdaquila Good Morning Carolyn , I think the OP is serious about deleting this thread .


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I know that’s out there, but I’m skeptical about it being a ‘miracle cat cleaner’. How many times have you used it successfully?

the OP’s posts with the links have been removed, but I’m sort of siding with them on this…flagging as spam was probably overkill. I see @Tester has a post above with a link and it’s allowed to stand…

i think sometimes the people on this forum lack empathy for new posters, even if the stated objective is to be welcoming. this and so many other forums have people who will denigrate newbies for not providing clear and complete information about what they’re talking about…what’s better than providing a direct link to the thing that some questionable mechanic recommended??

It’s not like OP claimed this product was a miracle-worker, or that it even worked for their vehicle. They’re out of work, desperate, seem to have a genuine issue, and they come here to find out if someone else is taking advantage of their ignorance.

We failed them here…




I apologize that I made you feel unwelcome. There are folks out there that use every opportunity to push products, but it looks like I was mistaken.

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Unfortunately your car may need extensive repairs and in my opinion the mechanic, in trying to save you money, did you a disservice.
Nothing you can do now, but for future reference, when buying a used car , if the repair for a check engine light was cheap and easy, the seller would have fixed it.

The disservice is that the mechanic appears to be guessing. The other problems are buying a vehicle from friends or relatives especially with the Check Engine Light lit . Also most people would not recommend an old used European vehicle for a persons first vehicle unless they are ready to spend lots of money.

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That is normal for all vehicle brands . So why did this relative not have the check engine light problem fixed before they sold it to you. Buying second hand parts yourself and paying to have them installed is never a good idea. If they are bad is he going to remove and put others on for free ? I still say you need to find another mechanic or shop and get this vehicle fixed .

Back in the days of Henry Ford, his car company was famous for manufacturing virtually every component that went into his cars. That was the reason for the construction of the incredibly massive River Rouge factory.

In more recent times, with the exception of the engine and the transmission, almost everything is purchased from outside suppliers.

I’ve had customers swear by it. I’m sure some swear AT it.

According to its MSDS, Cataclean has acetone, xylene, ispropanol, and light petroleum distillates in it. Not clear to me why those components aren’t just burned up in the combustion chamber. Gasoline already has about 5% xylene in it.

One guy did a test, saw no change:
CataClean: My Findings | MR2 SpyderChat

I don’t know how it works, but, like I said, some people have had it work for them. I can’t imagine it would do much for a severely clogged cat, and it would obviously do nothing for a physically damaged one.