Check engine again please help

5-25-13 PO420 $90 dealership diagnosis $100+ MAF sensor (autozone)

11-25-13 Light comes back on PO420 decided I'd avoid the dealer to save some money to diagnose $117 MAF sensor again. Replaced by Autozone for free cause of 1 year warranty.

3-3-14 CEL again. Borrowed my neighbors OBDII code reader and it gave me that same damn code again.

I got to looking through that scanner and it showed me the numbers that all the sensors are operating at and that was awesome but I can't find anything about what the sensors should be operating at. If anybody has any info to help me read this scanner rather than pay somebody $90+ just to tell me its the MAF again is greatly appreciated.

If it is the Maf again what is causing my truck to burn them up so quickly???

 

Do you have a cold air intake with a filter you oil?

 

No, I removed my k&n a long time ago and currently run a stock paper filter. I even closed off my deck plate hole.

 

Appears that your code indicates catalytic converter issue/ or exhaust leaks near O2 sensors, have you looked in that area?

 

^ This

PO420 does not appear to be related to the MAF sensor, from what I've read. You may have gotten bad advice originally, or mis-understood it. The problem lies in the converter, or one of the 2 sensors on either side of it. How old is your converter?

 

Are you getting crappy fuel milage or black soot on the tail pipe? If so that indicates the a/f sensor is bad.

 

YES!

P0420 is catalytic converter inefficiency. The computer compares the readings from the upstream and downstream 02 sensors and decides if the CAT is working at high enough efficiency. It sets the code if it isn't. Most of the time it's the CAT. An experienced tech with the proper scanner should be able to tell just by watching the sensor readings live with the truck running. I just had one of my CATs die, the dealer diagnosed it properly the first time, there was no mucking around with sensors, they went straight for the CAT.

I would take it somewhere else, have it fixed, get everything in writing, then if you feel it's appropriate, take the first dealer to small claims court. If you took it in for a P0420, with no other codes, with the truck still running good and they changed the MAF, they did you wrong. I'm sure that wasn't cheap.

I AM NOT A PRO MECHANIC! Take this with a grain of salt, I think my understanding is pretty good. As far as reading the sensors, I am not sure on the newer vehicles, with the older ones a sign of health was that they should "cross count" rapidly back and forth with .5 volts being the mid point. I think the newer sensors are higher voltage, I know a 2nd gen truck is for sure from watching my scangauge while I was having my CAT issue. This is for the front sensor that the computer uses to adjust fuel mixture. The rear sensor is just looking for excess oxygen, which should not be there if the CAT is strong. Excess 02 means that combustion isn't occurring in the CAT to burn that o2 off. If I recall correctly, higher voltage means more 02.

 

I cleared that code the other day and as soon as I started the truck yesterday the light casme back on. I hooked the scanner up to see the numbers of the sensors and it threw a P1135 which seems to lead to the O2 sensors. Back in May I replaced the rear sensor when i had a muffler installed.

Can anybody make heads or tails of these numbers? They were read at idle shortly after engine was started. I see one O2 sensor isnt doint much....

 

What dealer? MAF error codes are P01xx. Those guys are retarded, I would call back and get a refund. More likely you need a new AFR/O2 sensor. If not that, Cat conv.

 

Check for an exhaust leak. I replaced two O2 sensors and then found the leak which was the problem all along

 

I'm currently chasing the same code. Replaced AFR sensor, threw the code again. I took it in and my mechanic says one of my cats is bad. Called the dealer I bought it from, they told me they replaced one of the cats when they got it as a trade in. I live in MA and bought it in PA, so I had them send me a check to cover my costs for new cats. Had my guy put them in and the code came back. Anyone think I should've replaced the rear O2 sensor when I did the AFR? Truck runs great and I'm at my wits end with this check engine light...

 

I had the same code last summer. Checked the cats with a rubber mallet, exhaust leaks, temperature in and out of the cats, voltage and resistance of the O2 sensors. It ended up being a bad gasket on the rear O2 sensor that was allowing a leak. I just replaced the whole thing for $50, problem solved.

 

Saturday I received my Denso upstream O2 sensor from Rock Auto. Took me 10 minutes to change it and the light went away as soon as I turned the truck on so I would guess that was it. Thanks everyone for the replies!!