Oil pump failure or balance shaft module FAQ B5 VW Passat or Audi TDI engine
VW Passat, Audi A4, and A6 2.0L TDI engine oil pressure issues FAQ: from cracked engine oil pan, oil pump failure, oil pump chain tensioner, or balance shaft failureAlso see page 2 for the repair procedure and engine inspection. Page 1 and 2 of this article gives background and technical information, the other article deals with only the DIY replacement procedure.
The Passat TDI sold in North America from 2004-2005 has a decent engine, the BHW model. However, many cars have had worn oil pump hex drives, rounded sprockets, and failed chain tensioner/chains. These are part of the oil pump/balance shaft assembly and failure of any of these components will result in low or no oil pressure. If you see a warning on the instrument cluster that says STOP - low oil pressure, shut off the engine as soon as is safe and pull over to the side of the road. Do not risk getting into an accident to save the engine, always keep control of the car and concentrate on safe driving first. Your second priority should be to pull over and shut the engine off as soon as is safe. This tip also applies to any car.
The repair procedure below also applies if you lost oil pressure from a cracked engine oil pan and kept driving with low oil pressure. The engine oil doesn't dump out immediately unless there's a massive hole. If you hit the oil pan you should pull over as soon as is safe and inspect for dripping oil.
The Audi A4 and A6 TDI 2.0L sold in Europe in the same time period had the same problem, more on this below. The Audi A4 has never been sold with the affected TDI engine in North America.
Many Passat show excess chain noise and wear anywhere from 50,000-100,000+ miles. Cars have broken the chains/tensioner as low as 65,000 miles. This is just a range of cars that have been reported, diagnosed, and repaired. The actual statistics on dealer repairs or failures is unknown and I've heard cars over 100,000 miles that, in my opinion as a non mechanic (most mechanics wouldn't recognize this sound and problem either), aren't noisy. From what has been reported, noticeable noise/chain-tensioner wear/greater risk of breaking is around 80,000-150,000 miles. In my opinion, very few will last past 200,000 miles but your individual case may vary. The most obvious symptom is a rattling loose noise from the oil pan. Unless you listen to a Passat TDI with a tight chain and one with a loose chain, it's hard to describe the difference other than rattling chain noise.
Here's a video I made showing how the module works and a little bit about the repair.
Below are some example videos. Below left is a good running engine with 160,000 miles with minor chain noise. Below right is a bad 180,000 mile engine with a broken chain tensioner, worn sprocket, and low oil pressure.
Here is a good 60,000 mile engine with the gear driven module (I also did an engine swap):
Below left is a video from leicaman of a 56,000 mile engine with chain module. Below right is the same engine with the gear module.
Below left is a video of a 48,000 mile engine. Below right is a video of some pretty nasty chain noise on an engine with only 86,000 miles.
While I've experienced a broken chain and heard excess chain noise in another, a sample size of 2 means absolutely nothing. The reason the gear drive oil pump modification was started is because a few mechanics who specialize in TDI started to see many worn oil pump chains/sprockets/tensioners. As time went on, this became a well documented issue with many, many reported failures. There will always be a few defective parts that come off the assembly line and all mechanical components like chains wear out sooner or later, but in my opinion, the failure rate is abnormal considering the number of Passat TDI sold versus the number of reported oil pump failures and the relatively low mileage at which it occurs. This does not necessarily mean that every or even most Passat TDI will have this problem, just that the reported failure rate is high enough to consider this part a design failure. Nobody, not even VW-Audi knows the average time between failure for these parts and the percentage of cars that will have this problem, but they changed this design and if you want to not have this specific failure, the only sure way is to swap to the geared module or do the balance shaft delete with new oil pump. The delete will be more reliable, is significantly cheaper, and nobody has yet found the slightly increase vibration at idle objectionable. Because it's dimplier to install, there's also less chance for the installation to be messed up.
The most common failure is the tensioner cracking and a loss of tension on the chain. Here is one case where it was caught just after failure: the tensioner was barely in place and hanging on against the oil pan (click to enlarge).
Here are two more units for comparison. The one on the left came off an engine with about 55,000 miles, the right one had failed and worn away the sprocket teeth until the low oil pressure warning light came on at idle. If the car is giving the low oil pressure warning it's already too late!
Another failure is of the oil pump's allen drive shaft. It's explained some more in the magazine scan at the bottom. Here's a video illustrating a bad chain drive and the loose allen drive for the oil pump.
Here is an example of how sudden failure can punch through the front cover. The light is focused on the chain sticking out of the cover! This driver was lucky that it didn't punch through an inch to the right and throw the timing belt.
Similar engines on European Audi and VW 2.0L TDI had rolling changes from the chain driven pumps to gear driven pumps. Because the mk4 Passat TDI was only sold 2004-2005 in North America, we never saw these changes. There appears to have been a recall in Europe for "premature wear of the gears on the balance shaft module" on a similar 2.0L Passat TDI engine but I'm sure of the details or conditions because it applies only to specific cars built during June-Sept 2006. Here is a translated link to adac.de, a German auto site that has some details.
While mk4 and newer 1.9L TDI engines also use a chain driven oil pump, they run the pump at half crank speed (larger sprocket) and run only the pump. The 2.0L engines run the pump at twice crank speed (smaller sprocket) and also have to drive balance shafts. The chain tensioner, the part that is often the first to break on the 2.0L engine, is also different.
While it's frustrating, if you just look hard enough, many recent cars from many brands also have stupid design failures that can cause serious and expensive damage. Some examples are: a single capacitor on the ECU melting and destroying the computer which isn't available anymore or an inline oil filter on the turbo feed line causing oil starvation and destroying the turbo. Even B6 VW Passat with 6 cylinder engines had a recall where a bolt backed out of the oil pump, causing engine failure. This really wasn't a design failure but a manufacturing failure traced to defective bolts on the assembly line and only affected cars manufactured within a certain range, but it's a good example of how such a simple part can cause serious damage.
If you do/did have this problem, file a complaint with the NHTSA or Canada's auto safety agency. If enough people make a complaint it can start an investigation. It's possible that this could motivate a recall or TSB which could result in at least partial reimbursement of any repair expenses.
So why not sell your Passat TDI and buy a new Jetta/Golf TDI with the newer common rail engine which uses a gear drive oil pump? The newest generation Jetta grew and is comparable in size to a Passat but the Passat has many unique features like a sophisticated multilink front suspension, slightly better interior/rear room, projector headlights (can be safely converted to HID lights), very good safety ratings, and for those who don't mind automatics, a solid and proven transmission. ZF transmissions are also used in Audi, BMW, and Porsche. The TDI transmission is very similar to the one used in the same generation Audi A4/A6/A8. The new Jetta will get better fuel economy but the driving feeling is slightly different and you'll definitely spend much more money buying a new car vs. fixing your current car. Since depreciation is the real cost of owning a car, as soon as you drive a new car off the lot you've lost more money than the cost of this repair. And while the Passat BHW engine and 2009+ Jetta/Golf CBEA/CJAA engine have similar power ratings, the power comes on stronger and lower in the Passat. The Jetta's powerband is slightly higher but smoother and the engine is cleaner but more complex. The Passat engine is simpler with no post combustion injection or complex emissions filters. For a technical comparison of the engines, see 1000q: direct injection vs. pumpe duse vs. common rail.
How would you know if someone already changed your VW TDI or Audi TDI 2.0L engine to the gear module or (Europe) if it came from the factory with one? Here's how to tell.First, if the previous owner did the swap or paid someone else, they would know since it's not a cheap service. The sound before and after the module change is also very different because the gears are quieter.
If you're not sure if your Audi A4 TDI came from the factory with a geared module (all replacement new short blocks should have the geared module) you can try the dipstick test discovered by MOGolf. The dipstick on a chained assembly should have a little resistance at the very end of dipstick insertion. A geared assembly does not. In the picture below, you can see that the chain module slides the dipstick through the passage indicated below with the yellow arrow. The geared module has an open space and a wider hole so the dipstick doesn't have the same resistance. Unless you have experience, they'll probably feel the same to you.
If someone did a balance shaft delete (my current recommendation), you should not feel any resistance because the dipstick is going into empty space.
Here is another view. There are a few other minor casting differences, the most important one being the spot for the intermediate gear which is why you can't convert a chain module to the gear module.
Here is a view with the module in place. The dipstick got stuck to the side when I put the geared module on the engine, it should actually pass through the hole.
The proactive oil pump repair and more detailsFirst, if you have read a few articles on this site, you have found that they contain a minimum of editorial opinion and avoid scaremonger language. It's unknown how many cars are having this problem or will have this problem. However, any car or machine needs regular and preventative maintenance to run reliably so if you choose to do this modification, consider it preventative maintenance.
You could replace the chain tensioner/chain/oil pump assembly with an identical replacement part but it's recommended to either replace the chain driven balance shaft-oil pump with a gear driven assembly or completely delete the balance shaft assembly. Either method requires removing original oil pump assembly and balance shaft. While there were few direct replacement chain driven oil pump assemblies in dealer inventory, my opinion is that the gear driven oil pump assembly was more reliable. VW/Audi had a rolling change on a similar European TDI engine to this new part and the newest North American 4 cylinder TDI engines use a similar design. Credit for discovering the compatible parts and the original repair procedure goes to Oilhammer and MOGolf.
However, the most reliable repair is to completely delete the balance shaft assembly and replace it with an oil pump from an ALH diesel engine. The reason why it's more reliable is because the balance shaft assembly retains the hex drive for the oil pump which is a possible failure point. The delete conversion requires slightly more modification but is cheaper than the gear conversion and is slightly easier to install. The side effect is that removing the balance shafts slightly increases noise and vibration but nobody has yet reported it to be objectionable. See the installation article for the DIY.
The most common worn/failed components are the hex drive for the oil pump, the tensioner, and the sprockets. The hex drive had some problems rounding, possibly from vibration and loose chains. This causes a loss of oil pressure for the oil pump. The chains can break but this is probably due to the failure of bad tensioners or sprockets. The tensioners are breaking without warning, causing loss of oil pressure due to no tension on the chain. The sprockets are also rounding their teeth because of loose tensioners. The replacement gear driven oil pump/balance shaft assembly still uses a similar balance shaft but with a different oil pump and gear drive. It is not possible to retrofit the gear drive onto an existing oil pump assembly since the gear drive is part of the new assembly.
Other than the obvious problem of breaking tensioners, one possible contributing factor to failure is the speed of the oil chain sprockets. ALH engine oil pump sprockets also use a chain with a tensioner but they spin at half crankshaft speed and only run the oil pump. The BHW engine oil pump sprocket spins at twice crankshaft speed and also has to drive a pair of balance shafts.
The oil pump intermediate gear is part of the entire balance shaft assembly and cannot be retrofitted to your current oil pump/balance shaft assembly. As a side effect, the gear drive will quiet the engine. Part of this is the switch from chain to gears and part of this is the fact that most chains may already be making excessive noise. Because the increase in chain noise is gradual, it may be mistaken for normal when it's really just the driver getting used to the noise. If you listen to your car and another 2004-2005 Passat TDI you may notice a difference in the chain noise. If you completely delete the balance shaft assembly it will slightly increase noise and vibration. Other North American TDI engines do not use this assembly. There were similar engines on European VW and Audi TDI that used a similar balance shaft module and had a silent rolling parts change to the gear driven module.
Getting the dealer to repair it under warranty
Some dealers did repair the balance shaft module under warranty. I would not normally buy an extended warranty but if you feel you want to be proactive in repairing or protecting against this problem, it may be worth it to you. Some extended warranties can be used at independent repair shops but carefully check your warranty terms since most extended warranties are rip offs and will find a way to avoid paying claims. These cars are long out of warranty so most extended warranties will no longer cover it anyways.
It's not possible to have a dealer delete the balance shaft module. Even though the delete parts are all VW TDI parts, you're making modifications from another engine instead of bolting on direct fit parts.
If you hear excess noise and your car is under warranty, take it to the dealer and tell them that it's making excess chain noise. The first step in any warranty claim is your complaint. They must investigate the complaint and if they conclude there's excess or loud chain noise they must make the decision to investigate it further to find what is making the noise. If there is excess chain noise, they will find that wear on the oil chain/tensioner is causing the noise because it's the only chain on the engine. If your car is under warranty the repair is covered by the engine warranty.
Then you have to convince them to use the gear driven replacement instead of the stock chain driven assembly. There are still some chain driven assemblies in stock. The BHW engine on your car was not sold in Europe. The replacement part VW# 03g 103 295 q is off the European VW TDI engine "BGW". Since it makes sense to do the timing belt at this time I would also pay them extra to do it now. The timing belt has to come off during this job so the only extra part/labor is water pump, tensioner, and idler roller pulley installation. Also have them inspect the motor mounts for leaking as shown in 1000q: balance shaft assembly replacement - part 1.
Please see page 2 for the engine inspection and repair procedure (it's a separate article than how to replace just the module since that article assumes no engine damage)
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Here is some more info about the oil pump drive in Audi Driver magazine (it's the exact same part used on your engine):
Continue to page 2 for the TDI engine inspection and repair procedure