Mercedes CDI Diesel and Sprinter SCR Problems

I recently observed a factory Mercedes webinar for the complex problem of diagnosing and repairing Mercedes SCR systems for diesel cars and trucks and Mercedes Sprinter vans. We put this knowledge to use today for repairing a 2010 Sprinter van with an SCR problem.

SCR stands for Selective Catalytic Reduction and the vehicles that have it are usually labeled or badged ”BlueTec” It is the environmentally-friendly diesel technology from Mercedes Benz used to reduce emission levels. BlueTec uses Urea or diesel emissions fluid injection into exhaust gas stream in specially designed chambers in the exhaust to reduce emissions, especially NOx (oxides of Nitrogen).

The factory scan tool can be misleading and it is common for technicians to misdiagnose the system and change expensive parts needlessly. This fairly new technology uses the Mercedes SD connect to connect directly to the high-speed chassis CAN network of the vehicle. This allows monitoring of the raw sensor data and non-calculated information for precise diagnosis. The factory Xentry scanner cannot display and process this information the way this specially designed package can. On this vehicle we discovered a slight difference in the NOx sensor readings between the front and rear sensor and this led to diagnosing a faulty front NOx sensor. These sensors are around $600 at the time of this article but this is still way cheaper than if it was misdiagnosed as an SCR failure (currently $3700).

Cold Solder Joint Repair on Mercedes Module

At Autobahn Performance we can sometimes save money and time for our customers by repairing cracked or cold solder joints. Manufactures seem to use too little solder on some joints with high current/heat. The solder tends to crack over time. Our certified mechanics are experienced at repairing these circuits. Here’s an image of a recent circuit repair.

Audi Timing Belt

At Autobahn Performance in Ft. Lauderdale Florida we have done hundreds of timing belt services on Audis. We see some shops replace the belt but neglect to replace the belt tensioner, roller, or water pump. Failure of any of these components can cause the belt to break, causing major internal engine damage. Most Audi engines are interference engines and will break and bend valves if the timing belt breaks. At Autobahn Performance in Oakland Park (north Ft. Lauderdale), we use only high-quality replacement parts and dealer-trained technicians to perform a timing belt service on your vehicle.

Belt replacement intervals change year to year and model to model. The belts are made of rubber and will deteriorate regardless of the miles put on them. It is even worse for a belt to be rarely used than if it were to be used regularly. Timing belts should be replaced every 5 to 8 years, even if the vehicle has low mileage.

Porsche Cayenne Coolant Tee Failure (Plastic)

We are working on a 2008 Porsche Cayenne V8 Turbo. The vehicle developed a coolant leak behind the engine against the firewall. After painstakingly gaining access, we found that a cheaply made plastic coolant tee connector had become brittle and failed. We obtained a parts schematic from Porsche but nothing in the diagram looks like this. This part is probably a Volkswagen part as the Touareg is built on the same platform.

We could install a brass tee with hose barbs on it in place, but will give the dealer more time to produce the correct part. We may find that the part is available only as a hose assembly. We will add the correct part number and a picture of the new part when we find it.

Volkswagen 2.0l TDI Engine BHW Oil Pump / Balance Shaft Modification to Gear Drive Assembly

The VW TDI (Diesel) engine of 2005 is prone to problems with the oil pump assembly. The oil pump that came in the car is chain-driven and the pump also drives the balance shafts that smooths the engine vibrations. VW has updated the balance shaft and oil pump assembly to a gear-driven unit. The chain and chain-tensioner of the original style assembly wears and creates slack, lowering oil pressure. This can eventually break and cause no oil pressure and severe engine damage.

The oil pan needs to be removed to gain access to the assembly. (This also requires lowering of the sub-frame assembly.) The front lower timing cover / crankshaft seal fixture needs to be removed and the factory chain-driven gear pulled off the front snout of the crankshaft with a special puller. Ours came right off with the special puller. We’ve heard of difficulties removing the gear and having it break and needing to be chiseled or cut off. The new crankshaft drive gear needs to be heated to the proper temperature and it will slide right in place. There is no key-way for the drive gear. The balance shaft assembly is timed with a special lock tool. The oil pan and lower timing cover are sealed with sealant only — no gasket. Special VW approved Diesel oil must be used in these engines.

1981 VW Rabbit Broken Clutch Cable Bracket

Our good friend Rolf Engelfried had his very clean and original 1981 Volkswagen Rabbit Diesel towed in to the shop with a non working clutch. We had adjusted the clutch cable on a previous visit and thought the clutch may have failed. After inspection it was discovered that the clutch cable had broken its retaining bracket off of the steering column and the cable casing was pushing against the firewall instead of the bracket under the dash.


I remember working on a lot of these cars at my uncle’s repair shop J&R foreign cars of Lowell Massachusetts in the late 80’s and remember seeing this before. Unfortunately the only way to fix this properly is to completely remove the steering column form the vehicle and re-weld the bracket in place. We ground the old weld mostly off and cleaned the area on the column where the new welds needed to go. We welded the bracket on more than just the two ends that were welded from the VW factory. Here are some photos of the process.

Mercedes C300 Broken Rear Axle

It’s been a while since I needed to use this trick and it saved me (and the customer) about 8 hours of labor. This 2010 Mercedes C300 204 chassis vehicle broke the rear axle shaft (1/2 shaft). It sheared clean off where it comes out of the side of the differential. Vehicle was in a minor accident and somehow the axle twisted and broke. We used a miller stick welder and the largest diameter welding rod we had around. We let the rod get a good molten puddle going in the center of the broken axle stub and then pushed the electrode straight into the weld puddle stopping the arc.

We quickly unclamped the rod and shut the welder off. After allowing the rod to cool we used a slide hammer with a vice-grip attached to the pulling end (This is also a neat and useful trick / tool I made). I tightly clamped the vice grip to the end of the welding rod and with one good pull of the slide hammer the broken stub popped out still attached to the electrode. The new axle went in fine and everything worked good without removing and disassembling the differential.

Mercedes SL600 with Wiring Problems

We are working on a very clean and original 1995 SL600 (129 chassis) that has less than 30,000 miles on it. Unfortunately this vehicle was made by Mercedes with faulty wiring insulation that has deteriorated and caused short circuits in many components. The main engine harness (just includes the fuel injector wires and a few others) is in the worst condition. The main body mounted engine harness has some wiring circuits that are bad, Mostly the air mass meter harness. This harness is over$5000 for the part and approximately 60 hours labor to replace. It runs from the headlights to the trunk of the car, behind the dash and under the interior. This job at the Mercedes dealer could legitimately be $14,500. Just for the body mounted harness.

Here at Autobahn Performance Inc. in Ft. Lauderdale Florida we have developed a repair kit and procedure to repair this harness without removal for less than $1800. It will work on V12 engine in the 129 (SL convertible) chassis and the 140 chassis (4-door sedan or 2- door coupe). In rare cases more than the normal wire circuits are affected by the insulation deterioration and the harness is unrepairable. This is usually only in European-delivered vehicles and the sedan 140 chassis. If a wire suffers from insulation deterioration the entire length of wire must be replaced. Trying to splice onto a section of the wire will not work properly and will result in short circuits and possibly a fire. The insulation will start to crumble near where you are trying to repair it and you will probably make your problems worse rather than better.

The throttle actuators (electronic controlled throttle body, TBA Throttle Body actuators): There is one for each side of the engine. (note: the one on the right side of the engine feeds the air into the left side of the engine and vise versa) The actuators have a short wire harness coming out of them, it’s about 14 inches long, that connects to the body-mounted engine harness. These harnesses also have the insulation failure problem. The harnesses are part of the actuators and are not available as a separate piece from Mercedes. The Actuators can be rebuilt and new harnesses soldered into place. Again, do not try to repair these as you will not be able to properly connect new wires to the electrical connector end of the harness. Short circuits in the wiring of the actuators commonly cause damage to the E-GAS actuators (the control units that control the throttle actuators). These also can be rebuilt.

Mercedes Benz 107 Chassis Euro Bumper Conversion

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Mercedes Benz – Theft Relevant Parts (TRP)

Autobahn Performance is L.S.I.D licensed to purchase TRP parts. You do not have to take your vehicle to the dealer for TRP part replacement!

A new worldwide Mercedes-Benz anti-theft policy went into effect at Mercedes-Benz USA on November 10, 2008. This policy has specific requirements for the ordering and delivery of Theft-Relevant Parts (TRPs), which may require you to get information from the vehicle owner to place an order for certain spare parts. In addition, for certain theft-relevant parts, such as electronic keys, electronic ignition switches, infrared and other locking control units, it is mandatory for the dealer to install them. Please contact your local dealer for a copy of the policy so you can be better prepared to help them protect all Mercedes-Benz vehicles from theft.

Mercedes Benz claims the reason they classify parts as TRP is to keep your insurance costs down, on their vehicles.

Please visit Bob Beckmann’s great website that explains TRP and the difficulty shops like ours will face in the future if the parts that manufacturers can classify as TRP parts and their availability to the aftermarket is not limited by the lawmakers.

These Mercedes parts listed here are vague and could involve a majority of the repairs we perform at Autobahn Performance. We have the equipment and the capability to install all these TRP parts.

[1] Keys: electronic and traditional blade type (also green and orange programming keys
[2] Electronic Ignition Switch EZL
[3] Infrared control Unit, Drive Authorization Module DAS
[4] Locks and Lock Cylinders: mechanical and electronic
[5] Electronic Selector / Shift Lever Modules (electronic shifter assembly) on models 215, 220 and 230 only
[6] Transmission gear control unit (Electronic Valve Body on 722.9 G-tronic transmissions only)
[7] Engine Control Module
[8] Flashware or repair CD’s
[9] Certain Airbag / SRS supplemental restraint system cables, etc.
[10] Body Shell, certain body panels, and components

At Autobahn Performance Inc., we have been negotiating with our local dealers and with other affiliates to resolve this problem.

It is insulting to a reputable company like Autobahn that Mercedes and our local Mercedes dealers, that we have purchased hundreds of parts from over the years, that they would treat us as insignificant and do not trust us, or even think that we are stealing vehicles or parts from them.

If the dealers correctly fill out the paperwork and forms (as required) on the theft relevant parts that we purchase, there would be an obvious paper trail leading back to us, if a vehicle we had repaired, was stolen.

I am sure that there are companies out there that will do this, but there is no amount of money that could entice Autobahn Performance Inc. to knowingly become involved in the theft of a vehicle or parts and jeopardize our name and reputation for such a minimal profit. Our annual sales averages are in the millions of dollars; and to risk all that on some illegal activity is absurd.

Some of the parts listed seem to have no relevance to the possibility of using the part to steal a vehicle. How could you steal a vehicle with an ignition lock cylinder (with no key to it), or with an un-programmed engine control unit (ME control unit)? The only way that I can see is if you use that part to throw through and smash the glass window of a locked vehicle to gain access to the interior of that vehicle. I hope Mercedes is not trying to corner their share of the repair market by requiring customers to have their vehicle repaired at the dealer. This would be a monopoly and should be illegal. The dealerships seem to be using the TRP policy to their advantage by selectively enforcing their interpretation of the policy and requiring that vehicles be brought to them to be repaired when the sale of parts is refused due to the policy’s vague guidelines.

I think the reason that Mercedes is pressing this issue is to keep insurance costs on their vehicles down. If the vehicle is harder to steal or fewer are stolen, the customer’s insurance cost for that vehicle will be lower. In turn, Mercedes should sell more cars due to a lower cost of ownership.

If anyone has any further information or updates on this policy, please contact me. I would like to hear your stories and ideas on this subject.

On January 2012, Autobahn Performance, inc. became a licensed locksmith with a NASTIF LSID locksmith ID (a lengthy and expensive process). We can now acquire TRP parts and repair your vehicle without being forced to refer our customers to a dealer.

On 6/22/2009, Mercedes refused sale of an instrument cluster for a 2005 Mercedes CLK55 AMG. Customer’s cluster was totally dead, there was no communication and nothing at all lit up or moved. The vehicle still drove fine but soft top operation was locked out, probably due to the vehicle speed signal not being distributed on the CAN bus due to the failed cluster. The convertible top control module needs to know the vehicle speed to make sure the top is not being operated while the vehicle is in motion. Autobahn has the technology and the equipment to install the new cluster, but Mercedes and our local dealer, Mercedes of Ft. Lauderdale, refused to sell us the replacement part. The part has been ordered from an outside source and we should have the vehicle repaired for the customer in three to four days. This is normally a one day job if the parts are available locally.

On 7/7/2009, Mercedes refused sale of RCL or DAS module of a 2000 Mercedes SLK 230. Part number is 168 820 03 26. This vehicle has a current or hard code in the RCL locking system of B1000 internal module failure. This code will not clear / is always present. The customer also has a problem with intermittent engine CAN communication problems; when this occurs the transmission goes into limp home mode and does not shift. This problem may or may not be related to the DAS module but its replacement is warranted due to the B1000 code. We got the module from another source and it corrected the fault code. With this part alone there is no way to compromise the security of this vehicle.

As of 6/20/2011, Mercedes will not sell 722.9 valve bodies or conductor plate control units. Even with the TRP paperwork completed. The newer Mercedes 7 speed transmissions (also called G-tronic) have the electronic control unit mounted inside the transmission these control units are failing frequently; with speed sensor codes (the usual codes are related to speed sensor faults). The speed sensors are not replaceable as they are part of the electrical conductor plate that bolts to the valve body inside the bottom of the transmission. The transmission does not need to be removed to replace the valve body or the conductor plate. A valve body does come complete with the conductor plate / control unit. Early valve bodies must be replaced as a complete unit but later second or third generation units can be repaired by just replacing the conductor plate / control unit assembly. Autobahn has replaced many of these and have the capability of performing the SCN coding to complete the installation of this repair.

These units are failing so often that the dealer has restricted selling them even in their own shops. To order a part the dealer must submit a request with computer scans and control unit log reports of the suspected failed vehicles electronics. The factory then sends the parts they deem necessary for the repair (conductor plate assembly or complete valve body).

It is rumored that Siemens VDO, the manufacturer of the electrical control units is in a battle with Mercedes over the validity of failing units. Why should an internal problem with Mercedes and its suppliers affect our ability to acquire parts and repair our customer’s vehicle? Mercedes is requiring the vehicles be brought into one of their dealers for any valve body or conductor plate repair even if the vehicle is not covered under warranty and the customer is paying for it. Our customer’s view this would be perceived as an inability for us to repair their vehicle and give the dealers an unfair advantage at gaining the customers business. Losing a customer for ever could be worth 10’s of thousands of dollars.

On 10/19/2012, we installed our first 722.9 valve body since the “dealer only” ban. We probably have had 75 – 100 missed sales on valve bodies and conductor plates alone. We have established a non-local (can acquire next or second day) source. Installed and SCN coded with no problems. our source told us we would not be able to install the part and that the vehicle would need to be towed to a Mercedes dealer for installation. We Installed and coded this module to the car with no problems or delay’s. If your vehicle needs a new valve body, we can get this part and install it in your vehicle saving you a lot of money. Most importantly, keeping you from having to go to the dealer.