I have a 1997 F150, 4.6L,4x4, Fully Loaded.....CEL is on and have had it checked....


P0171
P0455
P0401
P0174

Now with that said....The throttle body has been taken off and clean, (was not even clogged), EGR valve replaced last year, DPFE sensor replaced last month... Where to from here......

 

Chevy Dealer

 

LOL ..

P0171 combined with P0174 is almost always the pcv line, usually the 90% rubber boot on the back of the intake, also check the line from the vapor management valve next to the power brake booster, the one with the green clip gets toasty near the EGR valve. P0455 could be a bad or loose gas cap - could be something else. P0401 could be DPFE or the vacuum regulator solenoid controlling the EGR or it could be plugged ports, burnt dpfe hoses or or or ..

use the search function it should help.

 

Replaced severla of the vaccum hoses to day when I pulled the throttle body off to clean it, the ones behind the throttle body, gas cap was also replaced 2 months ago, will check the PCV line tomorrow....

 

Lets go over your codes:
1. 171 and 174 are a pair attributed to the same fault.
.. What are they?
............A. fuel tables have shifted to their richest data setting trying to account for too much air in the mixture.
............B. unaccounted for intake air after the mass air meter.
............C. not enough fuel, making the air/fuel ratio to lean.
2. 401; is the test failure code for an EGR system test.
............A. blocked EGR passage into the intake.
............B. leaking metal tube.
............C. faulty DPFE.
............D. faulty EGR.
............E. faulty EVR/hose.
............F. electrical connection.
3. 455 is gas tank evap system operation fault. A leak detected as part of a test sequence.
...........A. fuel cap.
...........B. faulty canister tube
...........C. canister valve stuck closed.
...........D. fuel tank pressure sensor.
...........E. any associated hardware.
.
You have 3 different faults to address.
Suggest you chase the most important one first, being the 171/174 codes, then the 401 second.
Check code clearing only for the code being addressed, until you get it fixed, then move on to the next.
Work one at a time to keep the confusion under control.
Good luck.

 

After reading that last post I'm thinking if the EGR valve was stuck open it would cause the 171 & 174 codes.

 

Thanks Bluegrass, I guess I have a Saturday all filled up......

 

If the EGR was stuck open, the motor would run very rough and the 401 code would not be present for a low flow fault.
To expand; an open EGR would allow uncontrolled exhaust gas to flow into the intake. This would make the motor run very rough because exhaut gas cannot burn the second time and leans out the air/ fuel ratio to much causing the roughness.
The 401 code is a fail code after a flow test has been tried and detected by the DPFE as a low flow.
So a valve stuck open is at odds with a low flow test.
Old saying " you can't fool mother nature".
Good luck.

 

Ok guys My brother had a friend who figured it out...I tried all the suggestions....The guy took the passenger side fender liner out and found that the vacuum storage canister was missing....the truck had been wrecked previously and they never replaced it the hoses were hanging down. I didnt see them because of them being on top of the fender liner...

 

That will do it.
We answer on the basis of nothing funny has been done.
Good luck.