P0171 & P0174 codes on 2001 5.4
10-20-2017, 01:00 AM
#1
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P0171 & P0174 codes on 2001 5.4
My truck throws a P0171 code and sometimes a P0174 code when first run at outside temps under 50 deg F. Doesn't happen when first started. Usually comes on at a stop sign after about 5 miles. Once reset, it doesn't come back on unless it has sat for awhile. Cleaned the MAF and did a smoke test but no problems were found. Engine may have been too warm? Almost seems like it may have a cold vacuum leak that seals when the engine warms up. Any ideas?
10-20-2017, 02:30 AM
#2
My truck throws a P0171 code and sometimes a P0174 code when first run at outside temps under 50 deg F. Doesn't happen when first started. Usually comes on at a stop sign after about 5 miles. Once reset, it doesn't come back on unless it has sat for awhile. Cleaned the MAF and did a smoke test but no problems were found. ...
Do you have any broken exhaust manifold studs?
Tighten the exhaust pipe to manifold nuts.
I had a P0171 that would get set and found the exhaust pipe flange nuts were 3/4 turn loose.
10-21-2017, 08:16 AM
#3
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More than likely a vacuum leak. Number one suspect is always the PCV hose and elbow. When your CEL comes on after a reset does not matter. It has a process of checking, and will not always come on right away, or right when you start it.
10-24-2017, 08:56 AM
#5
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I don't follow...
Are you saying the CEL is on when you start it, and it shuts off when the vehicle is warm?
Are you saying the CEL is on when you start it, and it shuts off when the vehicle is warm?
10-25-2017, 04:31 AM
#6
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Starting out in cold weather with no light on. After a few minutes the light comes on. I read and reset the code and it stays off until the next time I start in cold weather and motor has cooled. Does not do it in the summer or above 50-60 degrees.
10-25-2017, 08:13 AM
#7
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So you are shutting it off, not the ECU?
By doing that, you are confusing the hell out of anyone trying to help you.
I stand by my original post (post 3) in that you have a major vacuum leak. Have you checked what I specified in that post?
By doing that, you are confusing the hell out of anyone trying to help you.
I stand by my original post (post 3) in that you have a major vacuum leak. Have you checked what I specified in that post?
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10-25-2017, 07:13 PM
#8
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He's clearing KAM. The PCM then needs time to complete the monitor/test. Since testing is done at different temps throughout the drive cycle. This clears all monitors as well. Nothing more than a waste of time vs tackling the issue (s). Hoping it's a comp glitch I expect lol.
10-25-2017, 07:57 PM
#9
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He's clearing KAM. The PCM then needs time to complete the monitor/test. Since testing is done at different temps throughout the drive cycle. This clears all monitors as well. Nothing more than a waste of time vs tackling the issue (s). Hoping it's a comp glitch I expect lol.
10-25-2017, 09:10 PM
#10
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Right. If the PCM could express itself, it would say, -why me? 
On the other hand, if warm idle in park is above 730 rpms = small leak. Above 750, = graduating to a large leak. There's a list of reasons for these DTC's. Start at the air box connections, IAT grommet and MAF o-ring. Easiest first that doesn't cost anything but your time. Then the PCV set -up or vise versa. All vac should follow. It's bound to be there. From there you dig deeper. Chances are you'll find it early on if thorough.
On the other hand, if warm idle in park is above 730 rpms = small leak. Above 750, = graduating to a large leak. There's a list of reasons for these DTC's. Start at the air box connections, IAT grommet and MAF o-ring. Easiest first that doesn't cost anything but your time. Then the PCV set -up or vise versa. All vac should follow. It's bound to be there. From there you dig deeper. Chances are you'll find it early on if thorough.