Haven’t really posted on something like this before but my cats got me fully stumped now. I am young, don’t know a super whole lot about cars, I work at a salvage yard so i know a little. My 2007 Honda Fit Sport automatic has been what feels like throwing itself into “limp mode” and not letting me shift gears, rev engine at times, or anything like that, just coasts until it reaches a speed it feels safe, usually 40mph while on the highway, 20mph if i’m just starting to go right after i park it. When it did it first time CEL came on with p0420, took a camera in the 02 sensor and discovered the front half of the cat was also clogging. Gutted the cat, and tried the car again, and no use. any ideas?

 

Limp mode means your engine's ECU has detected a serious fault with the engine or transmission. It reduces power so you don't blow it up by driving it some more.

p0420 means reduced catalytic converter efficiency in bank 1. It often means a bad cat, but it can also mean bad oxygen sensors, an intake or exhaust leak, or a fuel system problem like faulty injectors dumping raw fuel into the cat (which will clog it quickly).

It can also mean a problem with the cat itself. It could already be toast and nothing short of replacement will get the ECU to stop throwing the code.

Outlier idea: If the cat is installed too far back in the exhaust system - near the muffler and not the engine - the cat never heats up properly and throws p0420. Long shot but it does happen.

I get the feeling your problem is upstream of the cat. Might want to have the injectors checked out. If it is faulty injectors, you're killing the cat by dumping raw fuel, and eventually you'll need a new cat if you don't already.

 

Cat was for sure going bad, for testing purposes, we completely gutted the cat on the car and the problem remains, with that p0420 code, now since the cat is empty. I don’t believe it is an actual “limp mode” as there are no codes… (borrowed a buddies scanner)
Thank you

 

Your engine and/or transmission is obviously malfunctioning - inability to shift and revving - but no codes other than p0420?

I think your ECU might be fried. It should be sending a boatload of codes under that kind of distress.

 

I got a junk yard ecu already and can flash it to the car, i’ll keep posted. Thank you again.

 

My Live data is reading that engine load % is sitting way higher than normal, especially in drive
Park:25-30
Idling in drive:40
idling in reverse:40
and while driving, it spikes to 100% super easily, could this be a cause? i’m leaning towards a simple transmission flush if so.

 

Tranny problem? I doubt it.

Engine load higher than normal indicates something is wrong with the fuel delivery system or air/fuel mixture. The engine is working harder than it should without having to produce any power.

Vacuum leak, bad spark plugs, bad injectors, bad sensors.

And that's in addition to a possibly bad ECU if you're not throwing codes from all these issues.

 

Update, ecm is in and programmed and trans fluid has been drained and filled, driving it tomorrow to work seeing how it does wish me luck 🙏
Thanks again

 

Trans flush drove great for about a week, facing same problem again. Not sure if it’s from weather outside temp, or if it’s simply trans slipping or torque converter getting locked, but I’m at a loss. If it were to be the transmission, does anyone know a good place to get one? Thanks so much again.