This code doesn't get a lot of diagnostic love on here, and I'm trying to get a little specific before popping the hood.
One longer louder start yesterday, and lower than normal RPMs at cold start idle today when the CEL came on are the only symptoms.

13 GLK 350 with 150k. The plugs have 10K on them.
LPFP, fuel filter, fuel pressure switch, and fuel pump module replaced 10 months ago.

I'm leaning towards it being the high pressure fuel pump, but wonder if old plug wires or injectors could throw a P1CCF.

I've had the hpfp out twice, once for the pcv valve and when I swap the cam adjusters 15k ago. So I can do it again, but I want to be a little more specific than just throwing a new high pressure fuel pump in.

 

I googled it , catalytic converter below efficiency . iPhone —16 AI

 

I've been searching all morning and found nothing catalytic related. Could you hit me with that link?

Edit, I found one single post, on this site, where someone hypothesized it might have been catalytic, but like all the other threads on here with this code it went dead with no answer.
Would think there would be some performance issues no?
It just started with no check engine light and the idle over a thousand RPMs like it should be. One time it did start cold with low idle.

 

Personally, I'd be VERY leery of any "iPhone AI" results ... or any AI results, for that matter. It's all still very experimental - I've been a software engineer for over 30 years (now retired) and AI is still in its infancy - not ready for primetime.

I also do not search ONLY on this forum, when looking for technical guidance... I do the typical web-wide search.

Sadly, not many definitive answers show up for that P1CCF. The majority of answers point to your potential fix: high pressure fuel pump.

I've also read where folks recommend checking for associated faulty/ degraded wiring.

Unfortunately, I don't have a definitive answer either.

 

Yeah I am old enough to know that AI sucks *****.

Hey let's throw in a b2266 code for Gear range D or R cannot be engaged. That's happened once or twice since it's gotten colder.

Now I'm thinking a new battery would solve everything. And yeah I search everywhere too. Found someone on Reddit say a battery fix their P1CCF 🙄

 

Well, a degrading battery can have a boatload of side effects. Our 2014 GLK350 Base still has the original battery. (South Central Texas here).

Do a load test on yours to see if there's degradation... if yes, should be replaced anyway... then see if it "fixes" the P1CCF 👍

 

Maybe I typed wrong the first time , I think your on right track

 

iPhone AI is impressive. Only on 15/16. AI is automatic when searching . Accuracy I don’t know. It’s AI , in continual development, until it takes over 😯
Others said battery .did you test it? What is tested voltage rested for hours ? Should be above 12.4 . test and charge it. In this weather charge anyway. Below 12.2-12.5 it grows cancer ! Sulfation!

 

So I put a new battery in two weeks ago, it's been over 200 miles couple dozen starts and the P1CCF code is still in the background although it has never illuminated the check engine light since that one time.

Vehicle hasn't been unable to go into reverse since the new battery either. And I've noticed it seems to run even smoother, more peppy, and even better gas milage since the ECO now kicks on more frequently and stays on for an entire red light. I think that's a good sign the new battery was needed. For the record gas milage and performance have always been great.

How long should it take this damn code to go away, or become a bigger issue and show me something?

My blue driver scanner won't clear it. I'm honestly at the point I was thinking of pulling the - battery to clear it to see if it comes back, although I know that's not ideal, and I don't know why it didn't clear when I swapped the battery because I don't think I did it in under 60 seconds. That's how long the internet says it should take.

This code is so freaking mysterious. Most of the threads it pops up in there's a bunch of other fuel related codes and issues. The few threads where it's just this one code often points of battery.

Here's a screenshot of the fuel trim range on a little drive I did this morning. I don't know what that drop is but long-term seems right enough? Rail pressure is always in range and it never gives us a problem starting no misfires no hiccups.




It got a new low pressure fuel pump fuel pump module pressure switch and fuel filter 11 months ago and haven't had any issues.

I finally searched this in a manner that found me that AI answer pointing to catalytic converter, but when you read it's two sources they don't mention catalytic at all. I'm really not scared of AI taking over the world.

 

Have you ever replaced the auxiliary battery? The gassers with the Eco option use that small aux battery to run systems in the car while the engine is off when stopped at a light.

New main battery probably resolved 99% of the issue, a new aux battery would likely take care of the rest.

If the code is not active, that means the error is not active. If it remains that way for a set amount of drive cycles, the ECU should clear the code itself.

Lastly, it probably wouldn't be a bad idea to run a good fuel system cleaner when you get your next tank of premium fuel.

 

My findings are that the Aux. battery in the Gasser is responsible for very little. Eco is not an option but standard, at least for the N.A. market, on the facelift GLK. If your Aux battery is bad you get a warning message every time you start the engine. If the message is shown Eco Stop/Start is, by default, disabled - so, it's not running any systems. If you remove the Aux. battery the only negative is the recurring warning message. The positive is you no longer have to push Eco Stop/Start button, to disable the feature, each time you start the engine.

 

My experience is the same ... I think I posted a reply stating all that (or maybe not - memory has gone saggy since retirement). We got the Aux battery Warning on the dash ... no problems driving the GLK while it was "bad" ... after some days, I installed a new Aux to get rid of the dash message.

 

When I eventually replaced my Aux. battery I first disconnected the main battery. Then I connected the new Aux. battery and tried everything electrical I could - radio, door locks, light, fan, wipers, horn, windows etc. Nothing worked/nothing had power.

Same as your findings - although I drove a few months with no Aux. battery in place at all, either bad or new. No problems of any type.

 

My understanding is it has something to do with the electronic gear shifting. My GLK (Diesel) which does not have Eco start-stop, does have an auxiliary battery, albeit a smaller one.

 

The AUX battery in the eco start/stop GLK350 has only one function — that is to run the auxiliary pump in the transmission to enable immediate take off after eco stop. The main pump is driven by the input shaft and can’t provide pressure when the engine is off. It doesn’t power anything in the vehicle except that, consistent with what you’re all finding. That function is consistent across all facelift model 204s (W/X) with the eco function.

 

Then, why do I have one?




Could it be that yours does both functions?

 

Who knows? Diesels were different from gassers. FL was different from pre-FL. The ‘15s even had different components in places from the rest of the FLs.

The diagram, and a paste in page in my owners manual, said that my ‘15 GLK350 had a lithium ion battery in the console making total of 3 batteries. When I disconnected my main battery to change it years later, every component inside the car, radio, dash display, lights was dead. So I figured that the battery in the console had gone bad. NBD, the aux battery in the back was good and everything returned to normal when the new main battery was connected. Later, when I did some work on the A/C control module, I figured I would change the one in the console while I was at it. I went to buy one at the dealer parts counter, gave them my VIN, and they said “nope, don’t have one.” Curious, I looked anyway and there wasn’t a third battery. So if the auxiliary battery in the back of the GLK350 supports something other than the transmission auxiliary pump, its not obvious what it is. A MB trained acquaintance told me that there’s only one auxiliary battery charging circuit in the GLK, so it can’t have 3 batteries, but I didn’t query him on what the one in the back supported.

I have an ton of model 204 manuals and I still don’t get things right. And … we don’t have any 204s left in the local fleet which I help maintain.