MAF Sensor causing limp mode. - Club Touareg Forums
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post #1 of 18 Old 01-27-2019 Thread Starter
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MAF Sensor causing limp mode.

Hello all.
So this past week has been extremely cold where I live and has been causing issues with my V10. It doesn't like to start smoothly and it has been running really rough. I used a very basic code reader to scan codes and it said my MAF's were bad and something was wrong with a glow plug. OF course being a basic reader it didn't say more then that.

I finally took it in to a shop on Friday and they ran codes with VCDs. Again, found errors with the MAF's and a misfire code for cylinder #6. I already had new MAF sensors (I just haven't had time to install them). So the shop installed the MAF's, cleared all codes, and let it run for a good 20-30 minutes. No codes came back on. I drove it the 30 miles home and all seems to be good.

Here is my question. Should I still be worried about the glow plugs? Or do you think I will be ok for now?

P.s. I am still having issues with getting her started in this cold weather. It is still super cold out. I do need to change the fuel filter soon. Could that be an issue for not wanting to start?

Any advice would be greatly appreciated.

Thank You.

I will try and post the scans soon.
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post #2 of 18 Old 01-27-2019
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What does a glow plug do? www.yourmechanic.com/article/symptoms-of-bad-or-failing-glow-plugs

Quote:
Glow plugs are an engine management component that is found on vehicles equipped with diesel engines. Their purpose is to preheat, and help warm up the engine’s cylinders so that diesel combustion can occur more easily. They play an especially important part in warming the vehicle’s cylinders during cold starts, where starting the engine is most difficult.
Fix the bad glow plug, replace the old fuel filter, and run some diesel treatment in the fuel, especially during cold weather.
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post #3 of 18 Old 01-27-2019
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I don't understand how people post about having a problem which is giving them grief (hard starts) and then they ask if they should worry about it.

I say don't worry about it.... it certainly doesn't affect me or my cold starting.... just wait till it warms up and the problem fixes itself.
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post #4 of 18 Old 01-28-2019 Thread Starter
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I have a new fuel filter on order and will be replacing it as soon as it comes in (dealer had to order one for me. And yes I know I could have gotten it cheaper from somewhere else).

My next question is, why does it not crank for more than 2-3 seconds?

I put the key in the ignition, turn it to auxiliary mode, let the glow plugs warm up, I turn the key to start it and nothing.
The starter will make a noise for 2-3 seconds or revolutions and then stops.
I have to remove the key and start the process over in order for it to attempt to crank again.

She has no problems starting in warmer weather. She will fire every time during the summer. Which makes it hard to believe that there is a "flat spot" on the starter preventing it from turning over.
I have had this issue and a previous vehicle and it would cause this issue no matter what the temp was outside.

Any idea or suggestions?

I do plan on bringing it in to a shop soon, if I can get it started.

Please, I don't need more negative comments. I am looking for actual advice.
I already know that I should still be worried about the potential misfire and bad glow plug. But when all codes go away and don't come back on, makes me think that the 2 MAF's were a pretty big potential cause for that misfire. Or maybe I am just that dump.
Either way, If you don't have any actual advise, please don't waster all of our times.

Thank you to all.
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post #5 of 18 Old 01-28-2019
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The engine really needs all the glow plugs working correctly, if you want good cold weather starts. Otherwise, every single time it gets really cold, you are going to have cold weather starting problems. Every time it warms up, the problems will go away. The engine is pretty good at starting without the glow plugs as long as the temp is above freezing.

You are thinking of this as a old school engine. Turn it over enough times and it will eventually start. The rules of mechanical diesel physics no longer apply to you. You have a computer nanny between you and the mechanics of the diesel.

You don't even trigger the starter. You turn the key to start, but the computer decides if the starter relay is activated or not. The computer also decides for how long the start will turn. That is why you only need to flick it quickly to start and let off. All you are doing is asking the computer nanny to activate the start sequence.

The computer nanny can decide to do strange things. Such as deciding that it should use a secondary start method due to an error code being present. Such as doing something stupid during a startup when it sees a misfire in a single cylinder.

It would not surprise me if an error was present and then it sees a misfire, that the computer would just abort the start sequence.

This is one reason a full third of the forum will not answer someone unless a VCDS scan is also posted. You really can not do a lot without a scan. You can not properly repair a VW without a scan anymore.

Half the time, if you replace the correct part but you do not manually clear the codes, the computer keeps running the system as if the defective part is still on the engine. Clearing the codes is as important as replacing the defective part. You have to keep the computer nanny happy.

If you wish to be involved in the repairs, you need to get a proper code reader (VCDS-VCDS-VCDS) or just start dropping it off at the shop with a blank check and tell them to get it running and fill in the amount for you. The generic code reader is just not going to cut it.

PS: You really want to run a good diesel treatment year round but it is pretty much mandatory that you run a cold weather diesel treatment in cold weather.
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post #6 of 18 Old 01-29-2019
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Quote:
Originally Posted by ArgonSr View Post
Please, I don't need more negative comments. I am looking for actual advice.
I already know that I should still be worried about the potential misfire and bad glow plug. But when all codes go away and don't come back on, makes me think that the 2 MAF's were a pretty big potential cause for that misfire. Or maybe I am just that dump.
Either way, If you don't have any actual advise, please don't waster all of our times.

Thank you to all.
You are wasting the time of those who are "wasting their time" trying to guide you.... just keep throwing parts at it instead of doing it properly like some of us are suggesting. Negative or not, there's a right way and there's the way you're doing it.......

As stated by other wise users, today's vehicle systems are quite complex and rely on a lot of various things to save us from ourselves..... if you have sensors or components that cannot provide the inputs\values required, the system only gets "some" of the information required and starts getting in the way of things......

Good luck.
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post #7 of 18 Old 01-29-2019
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Ok, just went through this so here is what happened to me....

Read up on the glow plug and starting sequence and realized that even with new glow plugs and two new harnesses still got glow plug errors. Both batteries were tested and good but still had issues. Knowing that the battery under the spare tire was for the glow plugs I was confused as to what was causing a slow start.

Traced the wires back and found a mega fuse blown under the drivers seat. Replaced the mega fuse and still had issues? Then I tested the relay behind the trunk battery and found it to be bad. So I swapped it out with one I had in my other V10tdi and sure enough the starting problems swapped with the relay. This is what worked for me.

3 V10TDI's: (2)2004 Black/Black, Silver/Black and 2004 V10TDI in 1990 Corvette
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post #8 of 18 Old 01-29-2019
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That is one crazy problem starting problem Blownvette. Gosh-Dang computerized cars can be hard to fix.

This question is for the V10 owners.

We have an error code for a single dead glowplug on cylinder 6. We have hard starts when cold. Easy starts otherwise. My instinct is that the hard start will not go away until #6 glowplug is fixed.

Agree/Disagree? Also is there anything else you would check?

(thanks)
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post #9 of 18 Old 01-29-2019
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Quote:
Originally Posted by nickyt View Post
That is one crazy problem starting problem Blownvette. Gosh-Dang computerized cars can be hard to fix.

This question is for the V10 owners.

We have an error code for a single dead glowplug on cylinder 6. We have hard starts when cold. Easy starts otherwise. My instinct is that the hard start will not go away until #6 glowplug is fixed.

Agree/Disagree? Also is there anything else you would check?

(thanks)

What experiences have you had with glow plug faults?

Mine was a mystery #5. Would guess #6 would be similar as it is the end glow plug as was my #5? Can only relay my personal experiences. The first thing that should be done is understanding the system you are trying to diagnose. Or have a twin in the driveway to swap parts! Both ways take a bit of time from your day!

3 V10TDI's: (2)2004 Black/Black, Silver/Black and 2004 V10TDI in 1990 Corvette
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post #10 of 18 Old 01-29-2019
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Thanks for answering Blownvette. As a V10 owner, you were automatically included in the request.

You only had a single glow plug fault??? For some silly reason, I was thinking you had a multiple glowplug fault. That is 100% My bad. I didn't read your reply carefully enough. I see you stated it clearly.

I was thinking that an electrical or controller fault usually had a pair of the glowplugs go out together and assumed that a single fault usually meant that the glowplug itself was bad. <<Not necessarily true.

Well, I am glad I asked for further input. Something seemed off, so I wanted some more input. Little did I know that it was going to be me that was off. lolz.

To the OP: Blownvette is part of the core group of helpers on this forum. Or, to put it simply. If Blownvette says to he has seen "this" and that you should check "that", then you should check "that."

The sad part is that tracing and checking for electrical faults is beyond the scope of many owners. It is a specialty. But, lets make it really easy with a checklist. The OP or the garage the OP went to could check (if the OP can not).

Actually it might be pretty simple. Please double check this Blownvette. (thanks!)

1. Check every fuse under the seat/near the battery.
2. Would you recommend checking both the left and right hand fuse box and and the ones under the hood also? I am just double checking myself at this point. One goof a day is enough!
3. Check the relay in the trunk. I would assume we would want ohm's checked and the contracts visually verified as clean and non-pitted.
4. Done
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