For months now I've been getting a two CELs P0420 and P0111.


I'm running the Racing beat Intake & duct/ and have the Mazsport DR Mid Pipe.

I know that the P0420 is related to emissions and the lack of a Cat.

I know that the P0111 is related to the IAT (Intake Air Temp.) and the differences in temp. between the intake air and the exhaust temp.

However, I have gotten the P0111 since the install of the Mid Pipe. I have changed the MAF (IAT sensor is located in the MAF) not once but 3 times now in order to fix the P0111. Everytime I have changed the MAF I have removed the CEL with a scanner and disconnected the battery to do a reset.

Today I installed the 3rd MAF since this past April and drove 10 miles and the P0420 and P0111 code came back once again. I'm not to worried about the P0420. However, Could it be that I have a bad wiring harness causing the P0111? Is there something wrong with my PCM? Or, Could it that the midpipe is causing the issue? NOTE: I do have a Cobb AP that is ready to be installed to the car. But I'm waiting to see if a solution can be found before the install. I know that the Cobb can prevent certain CELs. Is the P0111 one of these CELs that should be masked?

I've been getting good gas mileage and the car seems to be running alright. Bottom line; will the P0111 cause any long term damage to the motor? And what do you guy think is a the fix for this combo of problems?

I'm sorry for all the questions that are asked in just this one post... But any help that you guys can bring to the table would be appreciated. Thanks In Advance

The IAT sensor is bad or the wring is bad. Its under and near the intake.

The IAT sensor is bad or the wring is bad. Its under and near the intake.

I was thinking the IAT was bad the first two times it was replaced. But now I'm thinking something else could be the problem like the wiring harness. Isn't the IAT located inside the MAF sensor? I'm pretty sure its all one unit.

they are generally in different places. lets consult the manual nope same sensor...

OK so there are 3 possibilities I can come up with

1) PCM is fubar

2) there is corrosion on the connector to the MAF/IAT or the ECT sensor

3) there is corrosion on the PCM harness or a bent prong

you can check for continuity if you think its the harness use pin D on the maf harness (consult the manual) put the positive on pin D and the negative on a ground wire if there is continuity your golden.

also you can check your ECT sensor it may be faulty sending messed up temp readings its located on page 288 in the #3 manual engine details.

Please look past the grammatical errors I'm dropping a deuce.

^^^ i do appreciate your helping out while taking care of business LOL. i will take a look for any type of corrosion. the car being a year old i think the possibility of corrosion will be slim. but i will check. I will look for a bent prong too and continuity. Where can i find the ECT sensor? i will have to get my hands on a 8 manual.

I'm going put my Cat and stock airbox back on this week reset the PCM and see if the problem continues. If so, its going to the dealer.

spelling errors are acceptable while on the pot. Haha

will this problem cause any type of motor issues now or in the future?

When I had this problem on my celica I noticed 0 problems and I ran with that on for 4 years. However that is a celica..

In all honesty the only sensors you need are o2, maf, coolant, and the fuel gauge. all the other bs is more for safety reasons. For example if the IAT were reading the same temps as the ECT that would be a safety issue...

That's why when you switch to a stand alone like haltech you wont see all the bs sensor's just the ones that keep the a/f in check and make the powwaaaaa...

To summarize if the car still runs performs and gets the same MPG I wouldn't go replacing a whole engine harness over it. However if its an easy fix like a bent pin or some corrosion id handle it.

P.S. If its your PCM this could be the calm before the storm and I'd get that replaced asap.

P.P.S. If you search on the forums there is a link to a website that hosts the entire service manual in PDF form

I found the link for the manual. there's a few sections that wont let me download 4,10,11. i think two of these sections could help me with my problem. I'm hoping for an easy fix. However its an 08, bought it less then a year ago. I've never played with anything under the hood so I'm thinking its a harness problem or PCM problem. Like i said in my first post all these issues started after my mid pipe install- have the racing beat intake for over 5,000 prior the mid pipe and the CELs.

I'm going try to take a look asap- as soon as the rain stops. But i/m very curious to see what will happen once i put in back to stock.

try the stock mid pipe back on with the airbox...

The p0111 getting thrown because of a mid pipe is slightly confusing but hey ya never know these cars have a mind of their own.

you need section 3 that gives you the pinouts. in the search field on the PDF document type MAF Sensor and it will pull it up, then type ECT Sensor and if you keep paging through it will show you where its located and how to replace it, you can also type IAT sensor they come off the maf harness but the pinouts are different on the PCM.

Thanks shady... your info will help a lot.

I hope so.. Goodluck and godspeed!