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Trouble code P219A?

Tiny
LEWISC13B
  • MEMBER
  • 2014 FORD MUSTANG
  • 5.0L
  • V8
  • 2WD
  • AUTOMATIC
  • 36,000 MILES
Hello,

I've asked a question about my issue before and have new information I believe may be helpful. My issue was that my car was idling rough, but only after shifting it to park or neutral. The RPMs bounce from 500 to 1,000, and it's only after driving then going to neutral or park, it idles fine at a stop light. I've been getting a pending error code P219A and have ran checks on it using a reader I got off of Amazon. I have tuned the car 4 times with different companies and on a dyno with no resolution. I've cleaned the throttle body, cleaned the MAF, changed the spark plugs, just replaced all O2 sensors, put seafoam in the tank and still nothing. The modifications are a cold air intake, long tube headers, and high flow catalytic converter X pipe.
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Tuesday, October 10th, 2023 AT 7:12 PM

10 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,885 POSTS
Please understand, due to the modifications, this will make it a bit more difficult to diagnose.

However, the code you have is specific to an air/fuel imbalance between the two engine banks. It can be caused by a few different things. For example, a weak fuel pump can cause it, an engine vacuum leak, or even an exhaust leak. Since you have installed headers, are the upstream oxygen sensors still present, and if so, are there any leaks in the exhaust pre-converter?

Do me a favor. Take a look at the pic I attached below. Note the list of possible issues/causes. Let me know if you have already checked the possible causes listed.

Let me know.

Joe

See pic below.
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Tuesday, October 10th, 2023 AT 7:52 PM
Tiny
LEWISC13B
  • MEMBER
  • 21 POSTS
Hello, honestly, I have not checked any of those. The issue with the rough idle was before the header installation, but the P219A code first appeared about 2 weeks after replacing upstream O2 sensors. I replaced them in hopes of resolving the rough idle. I have been keeping an eye on my STFT while driving, and what I noticed was bank two was always lower than bank 1. When I put the car in neutral or park, I'll see the stft drop to about -30 and catch back up eventually. If tried taking the car to a mechanic but my car won't let their readers work due to the tune. And I can't revert to stock without removing parts. Seems like I've dug myself a hole, lol.
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Tuesday, October 10th, 2023 AT 8:21 PM
Tiny
LEWISC13B
  • MEMBER
  • 21 POSTS
And yes, I do still have all O2 sensors. And I've tried to check for leaks pre cat by listening and feeling and I have not really noticed anything unusual.
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Tuesday, October 10th, 2023 AT 8:25 PM
Tiny
LEWISC13B
  • MEMBER
  • 21 POSTS
Hello, I'm back again. I had a new code pop up today and the CEL finally illuminated. The new code is a U401.
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Wednesday, October 11th, 2023 AT 9:57 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,885 POSTS
Hi,

Is it a U0401? If it is, that isn't even listed for this vehicle. I do know it is related to invalid information from the ECM. Please confirm that is the code.

Next, how long do the STFTs stay at 30%? That is excessive. To me, that would indicate a failed fuel injector that is dumping fuel.

Let me know.

Joe
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Wednesday, October 11th, 2023 AT 7:18 PM
Tiny
LEWISC13B
  • MEMBER
  • 21 POSTS
I apologize the code is a U401. Which came up as invalid data from the PCM. I took the car to AutoZone last night where they tested the battery and confirmed it was a bad battery, but alternator was good. Changed battery and will monitor it. For the fuel it will not stay at 30% long, I would say less than a second. When I changed the upstream sensors, I did not use Motorcraft brand, my friend is telling me Ford cars sometimes won't respond well to non-OEM sensors, maybe I'll give that a try and see if it clears the P219A code.
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Thursday, October 12th, 2023 AT 6:39 AM
Tiny
LEWISC13B
  • MEMBER
  • 21 POSTS
Is it possible that a bad battery could cause idle issues? I'm reading mixed opinions on the battery's effect on the engine with some claiming the alternator does all the work when the car is on and others saying that the alternator would have to work harder to charge the battery if it's bad.
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Thursday, October 12th, 2023 AT 6:42 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,885 POSTS
Hi,

A weak battery can cause all kinds of electrical glitches. Is there a reason you are questioning whether the battery may be faulty? If so, follow this guide and check the alternator output. Let me know what you find.

https://www.2carpros.com/articles/how-to-check-a-car-alternator

Also, the code you provided should be a letter (U) and a 4-digit number. See pic below.

Let me know.

Take care,

Joe
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Thursday, October 12th, 2023 AT 7:49 PM
Tiny
LEWISC13B
  • MEMBER
  • 21 POSTS
Hello, I apologize it was a U0401. Before this code showed up, I had some other weird codes pop up such as front wheel speed sensors invalid. I had both the battery and alternator tested and the battery was in fact bad. I replaced the battery and all my codes have magically disappeared.
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Friday, October 13th, 2023 AT 6:03 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,885 POSTS
Hi,

Wow! That's good news. Also, I appreciate the update. I'm glad to know it was an easy fix and you were able to resolve it.

Take care of yourself and feel free to return anytime in the future.

Joe
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Friday, October 13th, 2023 AT 8:02 PM

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