P0174 code after replacing thermostat housing

[John_H]

I replaced a leaking thermostat housing on my sister's 2001 4.0 Explorer. Prior to the repair, no check engine light. During the repair, I disconnected the battery and it seems once the computer cycled through that's when the check engine light came on. During the repair I had to move the air inlet with the MAF out of the way, separating the two sections.

My guess is I missed hooking something back up, maybe broke something, etc. But I've gone over it and can't see anything obvious at least. And it seems to be running okay, but I don't have the diagnostic tools to say for sure.

Any ideas? Thanks.

 

[Anime]

Welcome to the site!

P0174 is a code for a lean running engine (too much air / not enough fuel), so my guess would be that the air intake or the inlet stuff you moved around is either not assembled correctly, or it was somewhat fragile/brittle from age/cold outdoor temps and you wound up putting a crack in it that now leaks, and the air leak caused the code.

Best bet is check simple stuff first, especially the MAF connector if you unplugged it. It may just not be pushed in all the way.

You might need to redo what you did with the air inlet, or do it over with any tools needed to remove the air inlet so you can re-assemble it carefully. Check the connecting ends for cracked/torn/folded rubber sealing gaskets. It's easy to get a leak at the connections, especially on the bottom or back where you can't see. If you can, shine a flashlight into the inlet tubes at night or in a dark garage, look for any light showing through the plastic, indicating a crack and air leak.

You can seal any cracks with black or clear RTV silicone, or plastic epoxy might work. Getting a replacement tube is best, but a fix is fine until you can find a replacement part in decent shape if you need it.

Also be sure the screws and clamps are tight, from the air filter housing to the throttle body/intake manifold. Not too tight, but snug enough. Sometimes the clamps need to be positioned the exact same way they were before, they wear into the plastic or rubber and not seating them that same exact way results in an imperfect seal.

 

[John_H]

Thanks, Anime. I won't have access to the vehicle until the weekend, but I'll work through what you suggested.