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Check engine light on, code P0171 with a pending P0103 code?

Tiny
BILL MARTIN4
  • MEMBER
  • 1999 FORD EXPEDITION
  • 5.4L
  • V8
  • 4WD
  • AUTOMATIC
  • 250,000 MILES
My check engine light has come back on again. I checked with my Obd2 scanner, and it shows a P0171 code with a pending P0103. I have checked all hoses for leaks both with a smoke test and carb cleaner and found no leaks. I have replaced gas cap and replaced MAF sensor. After replacing MAF sensor it drove for a few weeks then the check engine light came back on with the above-mentioned codes. I also replaced the air filter. Any assistance is greatly appreciated. I can provide video clips of live data from scanner I took without engine running.
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Friday, January 5th, 2024 AT 3:21 PM

16 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
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Hi,

Based on the codes, my first suspect is you have an exhaust manifold leaking pre-catalytic converter on bank one.

These vehicles commonly develop a leak at the exhaust manifolds. If there is a leak, it can cause the system to think the engine is running lean. Also, since it is specific to one side of the engine, bank 1, chances are it has nothing to do with a vacuum leak. A leak would affect both sides.

I checked for the most common causes and the exhaust manifold is first followed by a leaking PCV hose elbow. See pic below.

Check both of these and let me know what you find.

Take care,

Joe

See pic below.
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Saturday, January 6th, 2024 AT 12:11 AM
Tiny
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Thank you, Joe. I will check and get back to you.
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Saturday, January 6th, 2024 AT 3:58 AM
Tiny
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Hi,

You are very welcome. Keep in mind, often an exhaust leak will sound like a ticking.

Let me know.

Joe
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Saturday, January 6th, 2024 AT 9:21 PM
Tiny
BILL MARTIN4
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No leaks were found near the exhaust manifold. I still need to check the PCV hose elbow. I couldn’t pull up the picture you sent, but I am pretty sure I know what you are talking about. One thing that I forgot to mention is when I took it to the shop and they diagnosed that the mass airflow sensor needed to be replaced, they said that it needed to be a specific one from Motorcraft, and they gave me a parts number I was unable to locate, the exact one that they recommended, but I got another one that stated that it fit that same part number. I will send you a picture of the invoice from the shop. Do you think that that would have anything to do with the problem I’m having?
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Wednesday, January 10th, 2024 AT 6:32 AM
Tiny
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Hi,

I can't do it from here, but the part number I have is different. I looked it up using your VIN. See pics below. See if you can cross-reference the one you got.

Let me know.

Joe

See pics below.
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Wednesday, January 10th, 2024 AT 5:35 PM
Tiny
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I crossed referenced and the one I got does match my vehicle. I got it from Oreily’s auto parts. To clarify what I was asking is do you think that there are other aftermarket sensors other than that specific one from Motor craft that the mechanic recommended that will work.
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Thursday, January 11th, 2024 AT 4:44 PM
Tiny
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He said that just about any other sensor other than that specific motor craft sensor will continue to have problems.
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Thursday, January 11th, 2024 AT 4:47 PM
Tiny
JACOBANDNICKOLAS
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Bill,

I haven't had any issues in the past related to the sensor brand. It is always a good idea to use an OEM part, when possible, but others work well, too.

Let me know.

Joe
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Thursday, January 11th, 2024 AT 8:16 PM
Tiny
BILL MARTIN4
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The mass airflow sensor that I bought is an OEM part. It no longer shows the pending P0103 code. P0171 is only code now. What is the best way to check for a leak at the exhaust manifold?
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Saturday, January 13th, 2024 AT 1:40 AM
Tiny
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Hi,

The easiest way is to listen for a ticking sound from the affected side. Have a helper hit the throttle while you listen under the hood. If there is a leak, the tick should be more obvious.

If you take a look at the pic below, that is the start of the diagnostics. Once that procedure is complete, the manual takes me to multiple other possibilities to check. If you want, perform the inspections and let me know the results. I can walk you through it one test at a time if you want.

Let me know. Also, is the engine running normally?

Joe

See pic below.
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Saturday, January 13th, 2024 AT 3:30 PM
Tiny
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I replaced the PCV valve tonight and reset the check engine light. I like your idea to troubleshoot each step to figure this out. To answer your question, the engine has been running great, and I have not noticed any ticking sounds, or sounds of a hissing hose. Hopefully this will solve the issue. I will let you know if the check engine light comes back on. I really appreciate your help with this matter!
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Saturday, January 13th, 2024 AT 11:40 PM
Tiny
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Bill,

No problem whatsoever. I'm glad to help.

Let me know how things turn out. Hopefully, the hose will resolve the issue.

Take care,

Joe
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Sunday, January 14th, 2024 AT 6:52 PM
Tiny
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Hey Joe, I wanted to let you know that replacing that PCV elbow that goes into the manifold seems to have resolved the issue. It was working great until yesterday the hose seemed to come off the metal piece that plugs into the manifold. I am wondering if there is an adhesive that may keep it on there or would that mess with the sensor? Any suggestions?
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Thursday, February 1st, 2024 AT 3:41 PM
Tiny
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Bill,

I'm glad to know that this has resolved the issue. As far as the hose coming off, are you able to get a clamp on it to tighten it in place? As far as adhesives are concerned, I suspect you could use something like a thin coat of Permatex and allow it to dry. I would just suggest finding something made to resist high temperatures.

Let me know.

Joe
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Thursday, February 1st, 2024 AT 6:49 PM
Tiny
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Okay, thanks so much for your assistance. I will look for a small clamp.
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Friday, February 2nd, 2024 AT 12:29 PM
Tiny
JACOBANDNICKOLAS
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Hi,

You are very welcome. If you have a chance, let me know how things work out for you.

Take care,

Joe
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Friday, February 2nd, 2024 AT 9:26 PM

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