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Flashing check engine light with codes P0172, P0175 and P0300

Tiny
JEFFROHOTROD1985
  • MEMBER
  • 2004 GMC YUKON
  • 5.3L
  • V8
  • 4WD
  • AUTOMATIC
  • 290,000 MILES
Hello, at first I had codes p0172 and p0175 when driving around town but noticed no problems when I would get on interstate or highway and driving at steady higher speed the light would go off and only come back on when stopping and going in city. Today it started running rough and the check engine light flashing. Ran codes same p0172 and p0175 and also multiple misfire p0300. Within the past year I have replaced plugs, wires, fuel filter, intake gasket and catalytic converters. Could all the codes be pointing to the same thing or what should I be looking at? Thanks
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Friday, May 28th, 2021 AT 6:39 AM

8 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,128 POSTS
Hi,

These two codes indicate an extremely rich fuel mixture. First, we need to check fuel pressure and the regulator. And yes, the rich fuel mixture will cause the P0300. The flashing engine light was indicating a misfire.

Here is a link that shows in general how to test fuel pressure:

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

Here are the manufacturer's specifications for fuel pressure.

Do this and let me know what you find. Also, let me know if you have a live data scan tool. If you do, let me know what the short-term fuel trims are.

Take care,

Joe
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Friday, May 28th, 2021 AT 8:03 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,128 POSTS
Hi,

I forgot to add the fuel pressure specifications. I did this time at the bottom.

I hope this helps. Let me know the outcome.

Take care,

Joe

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Sunday, May 30th, 2021 AT 5:54 PM
Tiny
JEFFROHOTROD1985
  • MEMBER
  • 12 POSTS
The fuel pressure with key on engine off was 50 PSI key on engine on was 45 PSI when snapping throttle psi went to 50 under load pressure stayed around 45. The freeze frame from when the code was set the stft bank 1 was -5.5 stft bank 2 was -11.7.
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Monday, May 31st, 2021 AT 7:17 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,128 POSTS
Hi,

The pressure sounds good. The trims indicate a rich fuel mixture. I'm wondering if there is a fuel injector or injectors leaking. When you checked fuel pressure (engine off), what happened to the fuel pressure when you turned off the key? Did it hold or did it drop somewhat quickly? Is the air filter in good condition and nothing blocking the air inlet?

The negative fuel trims indicate the computer is trying to lean the fuel mixture.

Let me know.

Joe
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Monday, May 31st, 2021 AT 8:39 PM
Tiny
JEFFROHOTROD1985
  • MEMBER
  • 12 POSTS
The pressure seemed to hold good it dropped about 5 PSI in 30 seconds but held around 45 for awhile. Air filters like new and no obstructions. I don't think it would be related but the mil came on today with a p0455.
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Tuesday, June 1st, 2021 AT 8:18 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,128 POSTS
Hi,

That code indicates a large leak in the EVAP system. Code 455 can indicate the canister purge valve is stuck open. This could draw fumes from the EVAP leading to a richer fuel mixture.

Do me a favor. The solenoid is on the intake manifold. Confirm the connector is tight, the wiring is good, and let me know what you find.

I attached a pic below showing the location of the part.

Take care and let me know.

Joe

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Tuesday, June 1st, 2021 AT 7:01 PM
Tiny
JEFFROHOTROD1985
  • MEMBER
  • 12 POSTS
The connector is tight and all the wiring and hoses looked good. Is there a way to test it or should I just go ahead and replace it?
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Wednesday, June 2nd, 2021 AT 9:26 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,128 POSTS
Hi,

I don't want to arbitrarily replace it because it may not be the problem. I have attached the diagnostics below for checking the system, but it does require a scan tool that can communicate with the vehicle. This is the only way to be sure of the cause.

Take a look through the directions and let me know if it is something you feel comfortable performing it.

Let me know.

Take care,

Joe

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Wednesday, June 2nd, 2021 AT 4:58 PM

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