What happens during programming
When a control unit is flashed, its old software is erased and new software is written block by block. With the ignition on, fans, modules and lights draw a lot of current. If the battery sags below what the module needs, the write can stop halfway, and the module may not start again until it's recovered.
The target: 13.0–14.0 V, steady
A battery on its own drops quickly under load. A proper programming power supply or a strong smart charger with a supply mode holds the voltage steady for the whole session. A small trickle charger is not enough.
- Use a charger or power supply rated for programming, ideally 30 A or more for larger cars
- Connect it to the jump points under the bonnet, not through the cigarette lighter
- Switch off lights, climate control and the infotainment screen where possible
- Close the doors and keep the key in range
Other things that break sessions
- Laptop going to sleep or running Windows updates mid-session
- Weak Wi-Fi: a cable or a strong signal near the car is best
- Loose OBD connector or a low-quality interface clone
Before your session with me
I go through this checklist with you at the start of every session. If something's missing, we fix it first. It's faster than recovering a module afterwards.
Frequently asked questions
Can I just leave the engine running?
No. Most programming needs the engine off and ignition on. That's why a charger is needed.
Is a jump starter pack enough?
Usually not. They're built for short bursts, not a steady supply for 30–60 minutes.