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08-13-2020, 02:49 AM | #1 |
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Drivetrain Malfunction - Boost Pressure Control & Camshaft Sensor
Hey folks,
Currently struggling to diagnose a weird issue with my F10 M5 2012. The car is totally standard with 82,000 miles. No warranty What's the issue? Typical drivetrain malfunction warning on the iDrive, then reduced power. Usually occurs after about 45 minutes of driving. If I then stop the car, turn off, it clears, but then can reoccur much more quickly when I get going again. It can also occur several times in the same journey. In all other respects the car runs fine. No smoke, no noises. As soon as the fault is cleared by switching off, it's back to it's best. What codes is it showing? 120408 Boost pressure control: shutdown due to reaction 164022 Inlet camshaft sensor 2, electronic short circuit to positive 120908 Boost pressure control 2, cut-off: pressure build-locked 120918 Boost pressure control 2, shutdown coupling: pressure build-locked What have I done about it? I took the car to my local BMW service centre who normally look after the car and, despite a few visits, they were unable to find a cause or solve it. To be honest, I got frustrated by the experience with them and gave up. You know how it is.. you have to talk to the tech via the service guy, so it's all so slow and frustrating. I've now got it in with a really reputable local BMW specialist and they definitely seem to be trying their best, but they're a bit stumped too. They've replaced the Inlet camshaft sensor, and updated to the very latest engine software (which is the common solution to the mixture of boost control codes). So far, it's not fixed anything. How can you help? The challenge here is that the issue is so hard to recreate. So, the mechanics try something, I pick the car up, spend a few hours driving it to see if it'll reoccur. It eventually does. Take it back to the mechanic and repeat. It's not their fault - But I don't want to be paying for some guy to drive my car around for hours, so I do that part myself. But, I wondered if anyone has seen this particular set of circumstances and had a strong view on a potential root cause? I'd like to avoid replacing lots of expensive parts as some sick game of whack-a-mole if I can! If it was something really obvious, I'm convinced that these two sets of mechanics would have found it by now. So.. I'd really appreciate any concrete ideas? Cheers |
08-14-2020, 06:36 AM | #2 |
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I wish I could give a "concrete" direction for you. When I was reading your post, my first reaction was the same as the your mechanics. Cam sensor shorted, must be the issue and it's causing the boost codes.
So what driving condition is causing the DTM? Are you just cruising along? Is it when you "tip in" to the throttle that it sets off the DTM eventually? Also, since the cam sensor was replaced, does that code return still? When was the last time the car was serviced, specifically topside of engine such as spark plugs, coils, injectors, etc. The direction I'm taking this line of questioning is to see if maybe a DME connector wasn't quite seated correctly. Typically when that happens you will get a lot more faults, but anything's possible. |
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08-14-2020, 11:58 PM | #3 | |
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Since I wrote the post above, the guys replaced the replacement sensor (to rule out a faulty replacement and then re-fitted/checked the connectors and..... so far, so good! Hard to be certain because the issue is so random - can be WoT, cruising or zero throttle, high speed, low speed, Comfort, Sport+, you name it. I’ve managed a 90 minute run and a few short runs since picking it up without issue (which bodes well) so hopefully sorted. I’ll update here either way. Thanks again for the post |
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08-15-2020, 08:17 AM | #4 | |
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Definitely will appreciate a final update if it's fixed. Will be a data point for someone in the future. |
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08-16-2020, 08:11 AM | #5 |
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Small update - thought it was fixed but.....not.
Seemed fine for a day or two but the inevitable ‘bong’ and message arrived on a recent journey. A quick scan shows the same issues, but is now reported on the Exhaust cam sensor 2 (when it was intake sensor last time). This tells me that either the task of replacing the intake sensor knocked or damaged the exhaust sensor, or it has also failed but was being masked by the intake sensor, or it’s decided to fail out of pure coincidence, or there’s something else going on. Oh well, back to the tech I go... Doh! |
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08-17-2020, 05:49 AM | #6 | |
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08-18-2020, 04:11 AM | #7 | |
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Thanks for the continued advice. |
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08-18-2020, 07:07 AM | #8 |
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It would also explain you short for sensor code that was thrown, the machine cant tell if it's the sensor itself or along the way just that it has a short for that line.
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08-25-2020, 07:21 AM | #9 |
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Small update - we've decided that, rather than immediately replacing another sensor or the harness/loom, we'd go for one final (conclusive) test:
They're swapping over the supposedly-faulty sensor from the exhaust cam side of bank 2, with the exhaust cam sensor of bank 1. I'll then do my best over the next few days/weeks to get the car to fault. Then, it'll either show a fault in bank 1 (meaning it must be the sensor that was moved over) or in bank 2 (meaning it must be the harness/loom on bank 2). Fingers' crossed for the former, as a sensor is a lot cheaper & easier than the harness/loom. I'll update once I know which it is Edit: It's also worth saying that it's definitely heat dependent. Hot days and warm starts cause it to typically fault within about 45 minutes. Colder days, cold starts can mean up to 2 hours before it faults, or sometimes no fault at all. I agree that probably points more to the harness/loom than the sensor but, could still be a sensor issue. To try and get it to fault then, I need to get out and get it really warm. Last edited by Mdifficult; 08-25-2020 at 07:26 AM.. |
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08-25-2020, 05:05 PM | #10 |
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Good luck!
BTW, given the heat factor, have you noticed if it does it more frequently or more quickly when the throttle is in economy or sport, as opposed to sport plus? Sport plus keeps the coolant temp noticeably lower. |
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08-26-2020, 02:56 AM | #11 | |
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Anyway, car is now picked up so I'll be driving it over the next couple of days and we should get conclusive proof of the issue. Lay your bets now... |
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08-26-2020, 12:11 PM | #12 |
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Progress!
Took the car out for a long run this afternoon using my new tried and trusted methods to build heat (low gears while cruising, high gears and full throttle when accelerating) and 'bong!' Parked up and a quick scan shows the following: 164030 Exhaust camshaft, electrical: short circuit to positive 164031 Exhaust camshaft, electrical: short circuit to ground 120408 Boost pressure control: shutdown due to reaction It's not saying which bank, so I assume that means bank 1. Which means, a second faulty sensor rather than faulty harness/loom on bank 2. This is good news Now the question is, with the inlet cam sensor already replaced on bank 2, and now the exhaust sensor seemingly also dead is it: A) The task of replacing the intake sensor knocked or damaged the exhaust sensor, killing it or B) It failed at the same time as the intake sensor, but was being masked by the intake sensor so didn't throw a code or C) It decided to fail out of pure coincidence. I'll almost certainly never find out, so looks like I'm in for two sensors rather than one. But, that's better than a new harness/loom for bank 2! Car's going back in tomorrow for the tech to confirm all of the above and make the fix, then fingers' crossed I should be at the end of this one. Let's see... |
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08-26-2020, 06:42 PM | #13 | |
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I personally do maintenance on advanced machinery(fanuc robotics and fanuc controlled cnc's) anyhow we had a machine at work that had one sensor that blew. Changed it with a new one and 10 minutes later blew that. The wire harness had a short to ground and would blow that sensor. The problem might of been you sensor, but it might be the harness that is killing your sensor, but it could also be a short that happens in the sensor. just odd that the problem persists with 2 different sensors. |
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08-27-2020, 06:49 AM | #14 | |
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Either way, this sensor needs to be replaced so I'm going ahead with that. If it fixes everything then happy days - and if one of the newly-replaced sensors fails then I know something's up with the harness/loom. I'm really hoping at this point that, with both sensors being original from new, both being in the same bank of the engine, and both having covered the same mileage in the same location, on the same DME, that it's not beyond the realms of possibility that they'd both fail in sync with each other. Should pick the car up this afternoon and then it's just a case of driving it over the next few days/weeks/months and seeing what happens. Again, big thanks for the thoughts and suggestions. As with anyone running a high mileage M5 without a warranty, I'm always just happy when the issue is something electrical rather than large bits of metal making a bid for freedom |
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09-06-2020, 07:35 PM | #15 | ||
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09-07-2020, 10:32 AM | #16 | |
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Fingers' crossed that's it for now - hope this helps anyone else with a similar issue. |
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12-08-2022, 03:02 PM | #18 |
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im also having this issue on x4m with s58. driving me nuts. happens as soon as car starts but drives fine otherwise.
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