Mercedes CDI diesel and Sprinter SCR problems

Jason recently observed a factory Mercedes webinar for the complex problem of diagnosing and repairing Mercedes SCR systems for diesel cars and trucks and 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 SDconnect 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). 

Another Mercedes V12 wire harness repair job.

Autobahn Performance is doing another air mass meter wire harness repair. We are getting lots of these cars in for the repair, even being shipped in from across the country. We can repair the air mass meter portion of the body-mounted engine harness without removing the harness. Do not attempt to cut open the body harness and repair the wires; this customer did and ended up cutting and damaging non deteriorating wires.

You can see in the pictures the wires are molded into a pass-through loom. It’s impossible to separate and untangle the wires without damaging the entire harness. We have repair harnesses in stock to repair the body-mounted engine harness on V12 600’s. Usually, only the air mass sensor wires fail. $295 each, 2 needed per vehicle.

The harness can be run alongside the factory harness, sheathed in long lengths of heat shrink tubing and connected directly to the engine computers. The other harnesses that often fail are the lower engine harness (also called starter harness or positive cable harness). We can repair your damaged harness but it may be available at a reasonable price from the dealer. (Get me your VIN and I will get you a price.)

The throttle actuators have harnesses that come off of them and connect to the body harness. These harnesses fail internally. To check them you need to carefully make a 1 to 2 inch incision in the covering of each actuator harness and examine the wires inside. If they’re bad we can rebuild your actuators (done in house): $695 each includes internal motor, plastic gears and new cable harness connector end is  disassembled and re-used.

The fuel injection harness sits on the top of the motor and is usually available from the dealer at a reasonable price. These can be rebuilt by us but must be inspected to give an accurate price. The body harness of the car usually does not fail or deteriorate on 129 SL’s. If it has deteriorated it probably should be replaced with new from dealer. (We could rebuild this harness but it would be expensive and time consuming.)

Clutch cable bracket broken on 1981 VW Rabbit

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 we 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 from 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 pictures:

Autobahn Performance has new diagnostic equipment

Autobahn Performance has recently purchased the Verus Pro d10 the top and latest diagnostic platform from Snap-On Tool Inc.

VERUS PRO Diagnostic & Information System Features
  • Stay connected to the vehicle and the internet while moving freely around the service bay
  • Ready faster – less than 30 seconds for VERUS PRO software suite to load
  • New thin-edge profile display tablet is 3 lbs lighter than previous model
  • Modular, dockable scope/meter with 9 ft USB cable for extended reach and portability
  • Exclusive SureTrack™ interactive community provides diagnostic experience, repair timesavers and parts replacement records from actual completed repairs
  • Genuine Windows® operating system for true multitasking
  • Shared vehicle ID – select the vehicle once for all diagnostic functions
  • Easy navigation – shows exactly the systems and tests available for the selected vehicle
  • Built-in browser and Wi-Fi to access your choice of web resources – parts suppliers, technical forums, repair information systems, OEM websites
  • Exclusive Snap-on Fast-Track® Troubleshooter provides millions of vehicle-specific code tips, symptom tips and timesavers for a faster repair
  • Industry-leading functions, tests and coverage previously found only in expensive factory tools
  • Avoid unnecessary parts replacement. Exclusive Fast-Track Guided Component Tests, component locator, known good values, and waveform library help verify good/bad components.
VERUS PRO Specifications
Display Tablet
  • Thin-profile tablet with 10″ high-resolution 1024×600 touch screen for a detailed view
  • On-screen touch keyboard
  • Built-in camera to save and share photos for your repair records
  • User-programmable shortcut key for frequently used actions
  • Bluetooth® wireless and Wi-Fi to access your favorite web resources
  • High-energy lithium-ion battery pack for hours of continuous operation
  • USB, audio and auxiliary ports make it easy to add accessories
  • Big 250GB hard drive to save data and install your own applications
  • Exclusive ShopStream™ integrated diagnostic suite with one-touch access to all major functions: scanner, scope, guided component tests, online expert forum, vehicle records, and the optional ShopKey® Repair Information System
  • Genuine Windows® multi-tasking to view multiple applications side-by-side
  • Configure display options, set triggers, record and playback results with the touch of your finger
  • Powerful data manager saves vehicle records, photos, technician notes, screen images, scanner and scope data
Scanner Module
  • Single keyless adapter for OBD-II vehicle applications – saves time
  • Connects wirelessly to the display tablet with Bluetooth® for remote operation
  • OEM-specific coverage for over 40 makes, as far back as 1980 (European optional)
  • Codes, live data, functional tests, relearns and adaptations for dozens of vehicle systems
  • Exclusive Fast-Track® Troubleshooter with millions of validated code tips, symptom tips and timesavers
Scope Module
  • More flexibility with the new hot-dockable scope module with 9 ft USB extension cord
  • High-speed 4-channel lab/ignition scope and digital/graphing meter
  • 6 megasamples/second sample rate and glitch capture detects faults other scopes miss
  • Scale range: 0-100mV to 0-400V, 50kV secondary ignition
  • Sweep rate: 50 microseconds to 20 seconds (5 min in GMM mode) so you don’t miss a thing
  • Exclusive Fast-Track guided component tests for 40 domestic, Asian and European makes
  • VDC, VAC, ohms, frequency, duty cycle, pulse width, diode test and more