Posted on 22 March 2014

When carrying out sensitive procedures on BMW vehicles such as Programming or Coding functions it is VITAL that the vehicle battery and electrical system is “backed up” by using a heavy duty, high current 13.8v power supply unit which is capable of a continuous output of at least 40 amps.

Because coding and programming can be time consuming and require the use of the vehicle ignition and main electrical system to be active throughout, using an external power supply in tandem with the vehicle battery is crucial in order to prevent against voltage drop outs and the eventual flattening of the battery due to the high continuous load which is placed on it, when having the vehicle ignition switched on. Even with the HVAC and other accessories switched off, the combined load of the DME / DDE and Fuel Pump(s) can create a load of upto 40 Amps which will flatten even a healthy battery in a short space of time.

Should the vehicle battery become flat during a precision programming operation, or worse still a voltage drop or sudden voltage fluctuation occur, then it may corrupt the data within the module, wipe the vehicle identity (VIN) from one or more modules, and essentially leave you with a “bricked” vehicle which will no longer start and will require expensive remedial work – probably more expensive than the problem that you were working on in the first place!. Therefore it is false economy to take a risk, and attempt to program or code the car using only the vehicle battery, and no external power supply.

You should avoid using conventional battery chargers to provide the external power supply, due to the fact that the output from these is either completely unregulated, or poorly controlled and relies on the state of the vehicle battery to determine the current output, rather than supplying a continuous load. These are NOT suitable for coding and programming operations.

BMW recommend that these operations are carried out using the power supply which their dealerships use, namely Deutronic DBL-800 model which is capable of a 45 amp continuous load  for older (“E” and “X” series BMW’s) . For newer (“F” series) models BMW Recommend using nothing but the Deutronic DBL-1200 model, which is capable of a huge 80 Amp continuous output.

Unfortunately both the Deutronic DBL-800 and Deutronic DBL-1200 Models are priced well outside the budget of most BMW owners and smaller workshops, costing an eye watering £1000 and £1500 respectively.

Luckily, most of these  Deutronic current ratings are well above what most BMW models will actually consume when sitting idle with their ignitions switched on and any non critical systems turned off, and once the electrical system settles down after switch on, the current consumption rarely goes above 30A – 35A, therefore with some careful planning, it is possible to use a much cheaper power supply with a rating of 40A – 50A continuous.

It is important, however, before embarking on programming or coding your vehicle to ensure that all non critical electrical systems are switched off to reduce the load on the main electrical system. These include HVAC / Climate control systems, Radio / Navigation, Wipers, Reverse Lights, Interior Lamps.

As an affordable alternative to the BMW Deutronic DBL-800 , we recommend using one of the following power supply units.










You should only use heavy duty, Automotive Electrical cable, rated between 120A and 150A for connection between the Power Supply unit and the Vehicle. We recommend using 135A 20mm (266 / 0.30mm) Hi-Flex cable in Black and Red .

This cable is sold by the metre and the cable length between the power supply unit and the battery should be kept as short as is physically possible. The ends of the cable  should be suitably crimped / terminated to allow connection to the power supply and battery terminals.

The specified power supply output voltage for Programming and Coding operations using BMW DIS / SSS and BMW ISTA is 13.8V – 14.0V and under no circumstances should the power supply unit be increased beyond 14.5V, or the vehicle started with the power supply unit still connected.


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