P3191 Code, Mass Airflow Sensor Replacement - Toyota Prius Forum : Prius Online Toyota Forums
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post #1 of 5 (permalink) Old 05-05-2012, 02:46 PM Thread Starter
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Default P3191 Code, Mass Airflow Sensor Replacement

I recently had to replace my Mass Airflow Sensor because the "technician" at Snappy Lube got mine dirty. The car was running fine when my daughter pulled in to get her annual inspection done, but when she drove away the Check Engine Light came on and the car was running horribly. She took it back to Snappy Lube, where they took it for a drive to see if they could see what was wrong with it. It died on them 100 yards from the store. I had to call a tow truck to get it towed back to my house.

Of course, they denied that they did anything, but I have no doubt that it was their fault. They got dirt in the MAF sensor while checking the air filter. By they way, there was no need for them to check the air filter. It's not required for a North Carolina safety inspection. They were just trying to make a buck off of my daughter.

So anyway... here's a video which shows how to replace the MAF sensor. You can probably do it without removing the air box by using a stubby screwdriver, but it's so easy to remove the air box I just did it that way.

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post #2 of 5 (permalink) Old 05-06-2012, 05:50 AM
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I think code 3191 is "failed to start" (however, I could be wrong, as this is just from memory). If you had an oil change at the same time, this code can also be caused by overfilling the ICE crankcase. I think it hold 3.7 quarts, and most shops just put in 4 quarts. The extra oil gets sucked into the engine, which causes a slight delay in starting, which throws the code. After that code happens, the ICE will no longer try to start.

The fix is to drain about a half-quart of oil from the crankcase, disconnect the 12v battery to reset the fail code, then reconnect the battery and try again. That usually fixes it.

I think later model Prius's lengthened the allowable time delay for the engine to start before the code was thrown, but that didn't fix the overfilled oil problem. We have had trouble with overfilling at our Toyota Dealer Service Center, too; so it's not just non-Toyota shops. After getting our car back with an empty crankcase one time, I always check the oil level after an oil change.

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post #3 of 5 (permalink) Old 05-06-2012, 03:22 PM Thread Starter
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Yep. You are correct. That is the descriptor for the P3191 code. In my case it would actually start for a few seconds and then immediately stop. Here's a nifty troubleshooting guide I found online which shows how to isolate the cause of the P3191 code.

http://www.hybrids.ru/PriusNHW20/rm/.../m_05_0191.pdf
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post #4 of 5 (permalink) Old 05-11-2012, 11:24 AM
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Reverend Sam,

Good info; I will save the MAF video and PDF file for future reference.

By the way, I think there was a recall on the cam position sensor years ago. If you still have problems, you might see if this was done. Toyota might do it for free, if it's necessary.
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One more thing: FYI, there was a recall on the steering box and power steering, last fall. Make sure to have this checked out, if you haven't already; because it can cause a loss of power steering.

Toyota replaced our rack and pinion box and power steering unit (several thousand dollars in parts and labor). So, after rethinking our decision to buy a new Prius next year, we decided to replace the shocks and put on a new set of tires. Now our 2002 Prius drives like a brand new car, but without the new car payments; and we have decided to keep it instead. We probably have another 100,000 miles before we will need to start shopping for our next Prius.
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