08-06-2021, 02:37 PM | #1 |
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P0172, aka BMW 118002, Fuel Trim
For those that may have battled a CEL from the the pesky DTC P0172 / BMW 118002, please follow along...
This code indicates a rich condition. P0172 is the generic code and the BMW diagnostic system (which goes into more depth) reports it as 118002. In both cases, it is a RICH condition. Most diagnostics start with a check of the turbo plumbing for leaks... and the same with the vacuum system. Mine has a few minor issues at 240K miles (LOL) but was easily fixed with a few new turbo seals. Next people suggest to clean the MAF, or even replace the MAF. Did both - the problem may have eased briefly but returned soon thereafter. There are a number of other sensors that people also call out here, like the MAP, the fuel rail pressure sensor, and even the diverter valve. All of that stuff was either new or got replaced and same thing - minor improvement at first then back to the same poor running and CEL. My car had a rough idle and an off-idle hesitation that would sometimes even result in the car (almost) stalling. It seemed worse if the car had the AC on or if the Eco Mode auto start/stop was engaged. Both at the same time was the kiss of death (made it easy to reproduce the problem). I solved this with some help from a local independent BMW service guy, who got me thinking about it in the right way after he had the car for a half day and charged me just 1 hour of diagnostic time. The key to the solution was using a blue-tooth based scan tool to monitor the Short Term and Long Term fuel trims in real time. What I found was that the car was desperately trying to take out fuel, showing as much as -29% adjustments despite still running rough. My Indy told me about a service bulletin that mentioned the need to update the engine SW to help address an 'overly sensitive' map that could result in rough running. Since I had been running BM2 Stage 2 for _YEARS_ , we agreed to skip out the SW thing. The Indy also called his BMW help line and a local dealership where he is friendly with the service manager. He was told that P0172/118002 is one of those codes that you just throw parts at. He called out that there are (3) items that the BMW dealer will do if the car is under warranty to ensure the issue if fixed in a single visit: 1. Change the Front O2 sensor (upstream) and possible the rear (if it looks bad) 2. Change the HPFP and then change the oil *oil change listed as REQUIRED 3. Change the Fuel Injectors and then change the oil * again oil change REQUIRED Since I had swapped both O2s already, I was looking at either the HPFP or the injectors. Out of curiosity, I asked why the oil change was required. This is where the moment of enlightenment happened.... The reason BMW tells you to change the oil after you swap the HPFP or the injectors is since if either one is failing it can result in gasoline making its way into your oil!!! The injector will leak into the cylinder and down the walls, past the rings, and into the sump. Here it will mix with your engine oil (YIKES) The HPFP is driven by the exhaust camshaft in the N20 engine. There is a cam follower that actuates the pump from inside the engine. When the seal on the pump fails, gas can leak past it and into the head and down into the oil (OH NO!!!). Aside from the scariness of having gas in your oil, here is why you get the P0172/118002 code, and also why it tends to get worse once the car is warmed up. The fuel that is now in your oil gets turned into gas vapor due to the heat of the engine oil during operation. Next, the super efficient PCV system on the N20 sucks up all that lovely vapor and routes it to the engine to be burnt. This is part of the secret to its good emissions, but when the oil is fouled with fuel it ends up sucking up a TON of vapors and triggering a rich code. Until I had the conversation with the Indy I was suspecting the injectors, since a failing fuel pump usually means a lean condition, not rich... IMHO, the reason(s) it gets worse when hot is because (1) the engine does not run in closed loop mode until it warms up so it does not 'realize' how rich it is until then and (2) the fuel in the oil vaporizes more slowly when the engine is cool and nearly instantly when the engine is fully hot. So, armed with my newfound knowledge, I bought the Bosch HPFP upgrade kit from the folks over at FCP Euro for ~$300 USD and installed all the parts in about 75 mins including removing and replacing the strut tower brace for ease of access (the Indy wanted $600 to do it). The difference was immediate. The car started right up and ran better and better as it warmed up. In the days that followed, it got better still - guessing it burned off all the soot from running rich for several months while I was trying to diagnose this issue. One tip for the install - before you button up all the covers and stuff... leave just the top fitting btwn the new HP supply line and the fuel rail hand tight. Next wrap it in a rag to catch a bit of fuel. Last, DO NOT TRY TO START THE CAR, just turn on the ignition. This will trigger the in-tank pump, which will force the air out of the pump and HP supply line. If you do not do this, you car will crank for 15-30 seconds before it starts. Not sure about you, but that would make me cringe, esp after the motor got 'cleaned' by fuel thanks to the HPFP failure. Interested to hear if this helps anyone.
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Last edited by pcking; 06-27-2022 at 01:37 PM.. |
04-22-2022, 08:30 PM | #2 |
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I want to thank you for this! I have been fighting with this code for a couple of months as well, and your post is the only one I could find that points the finger at the HPFP. I replaced MAF, TMAP, spark plugs, all with no luck. Once I put in the HPFP, all was right in the world! Thank you, I owe you a beer.
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04-27-2022, 12:24 AM | #3 | |
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06-24-2022, 06:26 PM | #4 |
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Man, I owe you more then just a beer!
Also after months of searching I found the cause of my hate for my BMW, thanks to your post! Almost forgot how nice it drives when all works well… Thank you so much for your time to write this. |
06-25-2022, 06:10 AM | #5 |
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Any mechanic, or service advisor that tells you "this is a problem you just throw parts at" is a moron and you should not do business with them. That clearly shows they do not know proper testing procedures. Yes many, most people, in the dealer world are inadequately trained as far as diagnostics go. They live in a world where they can throw parts at a car that dont fix it, and have an entire backup team there to convince you to pay for it anyway. Show them a labscope and they get all starry eyed. Mention an in cylinder pressure transducer and they are on the floor convulsing.
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06-27-2022, 10:02 AM | #6 | |
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06-27-2022, 01:43 PM | #7 | |
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FYI, my car has 289k miles on it!!! *LOL*
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06-30-2022, 04:25 PM | #9 | |
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DMM's, and oscilloscopes are the tools a TECHNICIAN uses to diagnose a car. A computer can not backprobe wires and take measurements. The dealerships model is to get cars in, fixed, and out as fast as possible for as cheap as possible. That means NOT EVERY tech gets the same training. 1 or 2 guys will get full on diagnostic training...But that doesnt mean your car goes to their bay. There is only 1 manufacturer that regularly calls out the usage of an oscilloscope in their diagnostic procedures...One! Hyundai/Kia. They supply reference waveforms and even show how to hook up the scope, for NON-TECHNICIANS. This guy right here, https://www.youtube.com/channel/UCR7...7-P541g2qlfRrg is an independent technician in europe. His channel is FILLED with cars the dealer could not fix. BMW included. If motherland BMW doesn't have the answer, then we're SOL over here 'across the pond' One of my favorites! Last edited by LA1Z24; 06-30-2022 at 04:36 PM.. |
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06-30-2022, 04:34 PM | #10 | |
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06-30-2022, 06:31 PM | #11 | |
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Just look at the forum for proof. How many people on this forum have paid the dealer to fix X problem, only to leave the dealer still with X problem. The "throw parts at it till its fixed" is a cover for IDK how to test that. |
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07-01-2022, 09:47 AM | #12 | |
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07-01-2022, 11:33 AM | #13 |
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Wishing you luck in that effort!!!
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09-01-2022, 12:54 AM | #14 | |
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Hi! Thanks for your useful tips! I have same issue on my f10 n20 too. I have replaced the HPFP. The problem still exist. Same code. I am considering the replacement of injector and o2 sensor. By the way, I have spend lots of money on this issue. |
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09-02-2022, 03:47 AM | #15 |
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Thank you for sharing with us your thoughts. Currently, I facing the same problem. I have been told with this code same diagnosis as you had mentioned many other things: O2 sensor, catalytic, etc.
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09-03-2022, 05:04 AM | #16 |
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Hi
Hi, I just wondering did you manage to how to fix the issue?
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09-03-2022, 05:08 AM | #17 | |
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09-03-2022, 05:44 AM | #18 |
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I have replaced O2 sensor as well and nothing. The catalytic converter has been washed/cleaned - nothing. Now they saying the catalyst needs to be replaced because the old one might be damaged really annoying issue.
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09-03-2022, 05:46 AM | #19 | |
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09-03-2022, 06:06 AM | #21 |
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09-15-2022, 02:06 AM | #22 |
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Post update
I have replaced HPFP problem gone.
Last edited by Raflus; 10-19-2023 at 06:48 AM.. Reason: Update |
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