Codes p0174 and p0401

[romeroabigail444]

I Desperately NEED HELP
My car desperately needed some repairs. My trusted mechanic replaced all 8 ignition coils and spark plugs. Now My car isn't shaking at all anymore when idling but here's the problem.///The check engine light came on after doing a smog check(probably because i haven't driven it yet)the smog check mechanic said to do a 60-100+ mile drove cycle.///And i noticed something BEFORE driving, my car usually has a 13 mpg range but it LITERALLY had 5.5 mpg/// I then started doing the drive cycle. 60-70 miles on the street and 200 on the freeway(until now) but it's only gone up to 11.2mpg, and only on the freeway it goes up/// I scanned my car using the autozone scanner and it emitted 2 codes p0174 and p0401. I'm not even sure if I completed the drive cycle or I simply need to erase the codes myself, I literally don't know/// My question is do I still need to drive My car so it can reach the desired mpg of 13-14 and then clear the engine light and the codes myself? But I'm my opinion overall the car doesn't shake when it's idling and feels pretty good
PLEASE ASK ME QUESTIONS.
I'm literally paranoid because I can't stop stressing about it (the codes)and the fact that I don't have a mechanic knowledge makes it worse.
If yall can recommend me to another subreddit that can help me, I'd be grateful

 

[Hamfisted]

Well the P0174 is a vacuum leak of some sort on the driver's side of the motor, and will contribute to bad gas mileage. The P0401 is a restricted EGR air flow, usually caused by a sooted up EGR passage in the elbow there on the throttle body itself. The throttle body and elbow have to be removed to clean out that EGR passage. Or you might be able to clean it out by removing the EGR valve and spraying some carbon cleaner in there ( CRC Intake Valve Cleaner is a good foaming cleaner...), and using a brass pipe cleaner or brush into the hole and rooting out the soot without removing the throttle body.

YouTube Video - Cleaning Out the EGR passage on a Ford 5.4








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[jr1under]

The info in the printed report is what you'd expect after the battery has been disconnected. Starting from scratch, some of the tests need multiple trips and types of driving before they can be performed.

 

[romeroabigail444]

Ah i see then so it's essentially just cleaning the egr valve and checking for any air/vacuum leaks that's making the car run too lean? ....... thank you

 

[jr1under]

Ah i see then so it's essentially just cleaning the egr valve and checking for any air/vacuum leaks that's making the car run too lean? ....... thank you

If you're lucky, that may be all that's needed.

After removing the throttle body cover(three 10mm bolts), look for cracked or brittle hoses in the vicinity. Or melted, as can happen if one touches the EGR valve. If the TB looks anywhere as dirty as the one in the picture, I would follow Hamfisted's advice and remove it so it can be thoroughly cleaned.

 

[EngineerMike]

both code causes could contribute to bad mileage, the EGR cleaning is simple as described above, hunting down the vac leak (which is likely the larger contributor to bad mileage) is hunt & peck. Vac hose replacement is probably best using aftermarket stuff rather than wasting time trying to get OEM hoses. You can get assortments of fittings and pliable hose at any good parts house or online.

 

[JerryT]

I Desperately NEED HELP
My car desperately needed some repairs. My trusted mechanic replaced all 8 ignition coils and spark plugs. Now My car isn't shaking at all anymore when idling but here's the problem.///The check engine light came on after doing a smog check(probably because i haven't driven it yet)the smog check mechanic said to do a 60-100+ mile drove cycle.///And i noticed something BEFORE driving, my car usually has a 13 mpg range but it LITERALLY had 5.5 mpg/// I then started doing the drive cycle. 60-70 miles on the street and 200 on the freeway(until now) but it's only gone up to 11.2mpg, and only on the freeway it goes up/// I scanned my car using the autozone scanner and it emitted 2 codes p0174 and p0401. I'm not even sure if I completed the drive cycle or I simply need to erase the codes myself, I literally don't know/// My question is do I still need to drive My car so it can reach the desired mpg of 13-14 and then clear the engine light and the codes myself? But I'm my opinion overall the car doesn't shake when it's idling and feels pretty good
PLEASE ASK ME QUESTIONS.
I'm literally paranoid because I can't stop stressing about it (the codes)and the fact that I don't have a mechanic knowledge makes it worse.
If yall can recommend me to another subreddit that can help me, I'd be grateful
View attachment 80483

Here’s another video which may be helpful. I would start with checking for a vacuum leak and replacing old hoses. I’ve had this problem on my 98 Expy and thoroughly cleaned the throttle body and intake manifold, there’s already a post on that. Good luck and don’t fret, you’ll get it fixed. https://m.youtube.com/watch?v=OFMexZ2kLNc