MAF sensor failure leads to DPF issues

[fujii13]

Just putting this out there for any other folks who find themselves in this situation.

Last week I noticed some soot buildup around the muffler and a little bit of rough idle and acceleration. I took it to the the dealer (yes I still go to the dealer as they have treated me extremely well with both my JSW and the Passat we have for my girlfriend both with the sale and service) and they said it was a simple MAF sensor issue and while the fix was cheap at only a half hour of labor, the part was not, reaching up to $300. I said go ahead and order it, and made an appointment for this Thursday since the part would not be in until Weds afternoon.

There was no indication that I should not be driving the car any different so when I had a beer event to head to in Lake George the next day, I didn't think twice about the 70 mile drive. About halfway up there, a significant amount of soot started coming out of the exhaust. A few miles later, the DPF light came on. I got off the highway so I can drive around in 4th gear a bit like the owner's manual states, but this does not help the issues. Still tons of soot, to the point where it is blackening the hatch. Later on, the check engine light comes on, but I do make it to my destination.

The beer event was a bust, the beers weren't that great and it was too cold for my camera to work so there was really no point in me heading up there. Oh well, decided to head back home after dinner with a friend, and while the CEL and DPF lights were off when I started the car, once I got back on the highway, not only did they return, but so did the cat light, and with all three, limp mode.

While in limp mode there was no soot but I couldn't keep up with highway speeds, especially not on the hills. Given that it was getting late and I was over 50 miles from home, I turned off the car and then back on so limp mode was disabled, and I was able to make it home with a pulse and glide technique, but any amount of cruising would cause limp mode to return.

When I called the dealership this morning and told them the story they said to bring it in and they had a car for me (a 2014 Beetle R-Line which is surprisingly zippy and sounds wonderful). Around lunch time they called me back saying they had the part and they could do the install that afternoon and I could be on my way.

Got to the dealership and the install was quick and easy. They took it out for a spin to make sure all of the lights stayed off and the DPF did a regen cycle. After waiting an hour, I knew something was up. Later, the service advisor came by to inform me that the DPF needs to be replaced due to the MAF sensor failure, and that it would typically be a $5,000~ cost but it was covered under the emissions system warranty.

So, they gave me the Beetle and I was on my way. The car is not expected to be done until Weds or Thursday at the earliest. Hoping for the best and no more surprises at this point. While I know the DPFs do not last forever, I was planning on doing a DPF delete plus Malone tune whenever mine failed. It gets a reprieve at this point.

Not sure what I could have done differently in this situation to prevent this other than just not drive the car when the CEL came on. I'll keep you guys updated as the rest of the story unfolds.

 

[OilBurningBrit]

Sorry to hear of your troubles, but glad you're covered by the warranty.

About the MAF sensor problem resulting in DPF failure though: I can see why it may lead to a clogged DPF, but if you were seeing significant soot at the tailpipe, I believe that indicates a cracked DPF ... and I don't understand how the MAF sensor could contribute to that. Did the dealer explain how exactly the DPF failed and what the linkage is between sensor failure and DPF failure?

 

[schultp]

...also, another forum member just had his dpf replaced for $2400. He had about 245K miles on his JSW and paid out of pocket for the replacement. The $5K cost quoted by the dealer either includes other items or is very high.

Paul.

 

[frugality]

...also, another forum member just had his dpf replaced for $2400. He had about 245K miles on his JSW and paid out of pocket for the replacement. The $5K cost quoted by the dealer either includes other items or is very high.

Paul.

tadurkee is a she. A courier of computer parts. She had her first DPF replaced under warranty at something like 20k, and then had the next one replaced 245k later, when she first learned that it should be checked, and it was found to be a bit over-loaded.

Someone else reported a $2200 DPF replacement bill.

 

[schultp]

tadurkee is a she.

Thanks. Hard to determine gender from online usernames.

 

[ticketed2much]

Sounds a little fishy to me. Was there a CEL for the bad MAF?

 

[fujii13]

The $5K was less a direct quote and more of a "I've seen that go for up to $5K!" while telling me it was all going to be covered. I'll know the full amount of what it actually costs when I get the invoice. As long as VW is paying for it, I don't really care what the dealership feels like charging them.

Sounds a little fishy to me. Was there a CEL for the bad MAF?

There were CEL, DPF and Cat lights on, not sure what was for what.

 

[n1das]

Sorry to hear of your troubles, but glad you're covered by the warranty.

About the MAF sensor problem resulting in DPF failure though: I can see why it may lead to a clogged DPF, but if you were seeing significant soot at the tailpipe, I believe that indicates a cracked DPF ... and I don't understand how the MAF sensor could contribute to that. Did the dealer explain how exactly the DPF failed and what the linkage is between sensor failure and DPF failure?

Sounds a bit fishy to me. Back in the pre-DPF days not too long ago, while smoke generally indicates something "bad", it was useful as a diagnostic tool. Now with DPF equipped diesels, the DPF does a good enough job of hiding smoke that you could have a smoke problem and not know it until the DPF is clogged up.

Since you were getting a LOT of smoke, something is really wrong. It could be as simple as an intake pipe came off from where it should be and you have a boost leak. Does the engine sound louder than normal and/or can you hear the hiss of a major air leak from under the hood when you get on the power? Prior to it dropping into limp mode, was power down at all?

Usually a dead or dying MAF sensor leads to a drop in power and LESS smoke due to the MAF under-reporting the actual amount of air. The ECU responds by reducing fueling accordingly. The other effect I've experienced is you can get more smoke with a dead MAF due to you catching the engine off-boost more often when you get on the power. The third scenario is the MAF output is pegged at maximum (unlikely to happen) and over-reporting the amount of air and causing fueling to be increased and resulting in more power but also more smoke. You may or may not get a CEL code for a MAF failure, depending on the failure mode. Also if you try unplugging the MAF, a default limp mode value will be used by the ECU and may throw a CEL code. Unplugging the MAF is useful for troubleshooting. If power improves with the MAF unplugged, the MAF is bad. If power drops with the MAF unplugged, the MAF is good.

Since a MAF usually under-reports the amount of airflow when they die and causes the ECU to reduce fueling, I don't think the MAF actually caused the smoke show and DPF getting clogged up. I suspect something else is wrong. It could be an intake hose downstream of the turbo popped off because the dealer mucked with it during the first visit. With no boost from the turbo you will get a ton of smoke, enough for some to get past a DPF and clog it up in a hurry.

Good luck.

 

[30_Yr_Dsl_Veteran]

Someone else reported a $2200 DPF replacement bill.

Simply just don't replace it - it is a superfluous item!!!