Fiesta ST P2279 Issue

[Mst]

Hi everyone,
I have a 2015 Fiesta ST and I’m dealing with an issue that no one has been able to properly diagnose.

After driving for a while (usually 15–20 minutes, once the engine is warm), a spanner light appears with “Engine Service Now”, and the car goes into limp mode. After restarting the car, everything goes back to normal.

The issue is very inconsistent — sometimes it happens every day for a week, then it disappears completely for 1–2 weeks.

What’s been done so far:
Cleaned the MAF sensor
Replaced the MAP sensor
Smoke test initially found a leak at the valve cover, which was replaced - After that, the car ran perfectly for about 3 months, but now the same problem is back

Now I did smoke test again - no leaks found
Fault code: P2279 (intake air system leak)

Additional thing I noticed:
On cold start, RPM sometimes fluctuates briefly while dropping, then stabilizes

Has anyone experienced something similar or knows what could cause this, especially with P2279 but no visible leak?

Any help would be really appreciated!

 

[SteveS]

If you checked all the vacuum lines and there's no leak, it could be a damaged or faulty PCV valve.

 

[MHBGT]

Hi everyone,
I have a 2015 Fiesta ST and I’m dealing with an issue that no one has been able to properly diagnose.

After driving for a while (usually 15–20 minutes, once the engine is warm), a spanner light appears with “Engine Service Now”, and the car goes into limp mode. After restarting the car, everything goes back to normal.

The issue is very inconsistent — sometimes it happens every day for a week, then it disappears completely for 1–2 weeks.

What’s been done so far:
Cleaned the MAF sensor
Replaced the MAP sensor
Smoke test initially found a leak at the valve cover, which was replaced - After that, the car ran perfectly for about 3 months, but now the same problem is back

Now I did smoke test again - no leaks found
Fault code: P2279 (intake air system leak)

Additional thing I noticed:
On cold start, RPM sometimes fluctuates briefly while dropping, then stabilizes

Has anyone experienced something similar or knows what could cause this, especially with P2279 but no visible leak?

Any help would be really appreciated!

I've been grappling with this same issue for a few years now. Ford could never fix it even under warranty, as it was too intermittent. The car is no longer my daily, so I've slowly been gathering parts and upgrades to throw at it.

After my engine rebuild, it started occurring more regularly, but even with a smoke test, they could not determine the cause.
It seems to get better for me in mild weather, 23C -28C outdoor temps, and occur more often at high and low ambient temps. So that leads me to believe it is a valve, connector, or seal that is intermittently failing during the driving cycle when things are either too hot or cold. My car is about 12 years old now, so it could be any of the pipes/gaskets plastic housings or even the PCV valve on the valve cover that is causing it.

My prime suspect is the pipework around the PCV system. I'll try replacing it with a catch can kit (with new pipes) that might solve two problems, but will keep you posted.

 

[Mst]

I've been grappling with this same issue for a few years now. Ford could never fix it even under warranty, as it was too intermittent. The car is no longer my daily, so I've slowly been gathering parts and upgrades to throw at it.

After my engine rebuild, it started occurring more regularly, but even with a smoke test, they could not determine the cause.
It seems to get better for me in mild weather, 23C -28C outdoor temps, and occur more often at high and low ambient temps. So that leads me to believe it is a valve, connector, or seal that is intermittently failing during the driving cycle when things are either too hot or cold. My car is about 12 years old now, so it could be any of the pipes/gaskets plastic housings or even the PCV valve on the valve cover that is causing it.

My prime suspect is the pipework around the PCV system. I'll try replacing it with a catch can kit (with new pipes) that might solve two problems, but will keep you posted.

Definitely keep me posted if you find the solution, I'd really appreciate it👍