P1179 Message diagnosis runs and drives fine?

Tiny
TWOZZIE
  • MEMBER
  • 1997 LAND ROVER DEFENDER
  • 4.0L
  • V8
  • 4WD
  • AUTOMATIC
  • 150,000 MILES
Car runs and drives fine, no problems apart from the P1179 message. The 4 areas of diagnosis I think are MAF, Vacuum, O2, Fuel Pressure. MAF was cleaned as is good. Vacuum hoses are all good. I tested Fuel pressure and its 32 at KOEO and drops to 28 when at idle. Manual says pressure should be 34-37 although I heard it should be 27-31? I changed out the Fuel Filter and tested the FPR (both were replaced in 2021) no fuel in the vacuum hose, removing the hose caused the pressure to increase to 32, blanking off the return line forced the pressure to 50+ and then held there. Never seen any leak down. I had a New old stock FPR so I changed it out regardless but nothing seemed to change per se. Now Im looking at the sensors and attached is one of the scanner screen shots. I think B2S2 looks like an issue but I cant be sure. Any help is appreciated
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Thursday, January 8th, 2026 AT 11:58 AM

6 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,182 POSTS
Hi:

You are correct. The code is related to a few things; however, something is causing a misfire.

I attached the possible issues below. Here is what I need you to do. First, you will need a live data scan tool.

I need you to allow the vehicle to reach operating temperature first. Then, we need to check the fuel trims. I suggest starting with this because something as simple as a vacuum leak can cause a lean fuel mixture and cause this. On the other hand, excessive fuel pressure can cause a rich mixture. That can be caused by a pressure regulator.

If the fuel trims are within specification, at the same time, check the mass air flow rate to determine if it is working within spec. The specifications are listed in the pic below.

Let us know what you find or if you have other questions.

Take care,

Joe

See pic below
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Thursday, January 8th, 2026 AT 8:00 PM
Tiny
TWOZZIE
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  • 9 POSTS
Hi Joe, Fuel trims as per attached. Will get the air flow today. Cheers
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Friday, January 9th, 2026 AT 7:26 AM
Tiny
TWOZZIE
  • MEMBER
  • 9 POSTS
Also Joe, how did you determine there is a misfire as the car starts and runs fine, no issues, cheers, Ewan
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Friday, January 9th, 2026 AT 7:46 AM
Tiny
TWOZZIE
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Sensor voltage
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Friday, January 9th, 2026 AT 8:44 AM
Tiny
TWOZZIE
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  • 9 POSTS
Mass airflow
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Friday, January 9th, 2026 AT 8:45 AM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 54,475 POSTS
JACOBANDNICKOLAS is one of our best!

P1179 = Long-term fuel trim too lean - Bank 2

This shows one bank lean but it looks like both banks are lean, thanks for the scan BTW, this helps with the diagnosis. So this is classic lean condition which can be caused by low fuel delivery, vacuum leak, or the MAF sensor is going bad. So I would check the intake tube between the MAF sensor and throttle body. Then replace the fuel filter, here is the location and then check for a vacuum leak, this video will show you how.

https://www.youtube.com/watch?v=LRKWV4Are5c

this guide does a great job with lean conditions you can go over for more information

https://www.2carpros.com/articles/repair-lean-mixture-codes-p0171-or-p0174-on-some-manufacturers

Clear the codes once completed. Check out the images (below). Let us know what you find.

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Saturday, January 10th, 2026 AT 8:56 AM

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