BMW 640 F13/F12: Tracking Down a Battery Drain and a Smart Keyless Go Repair

This BMW 640 wouldn't start after standing. The battery drain came from a faulty Keyless Go handle, which we replaced cost-effectively.

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CarBMW 640i F13 (3.0 petrol)
ServicesBattery drain diagnosis, Keyless Go handle replacement
Date22.05.2026

How the job went

Problem

After standing for a short time, the battery went flat and the car would not start.

What we did

We measured a 0.5 A drain in sleep mode and traced it to a faulty Keyless Go handle on the passenger side. We fitted a used genuine handle in the car's colour.

Result

The drain is gone, the car goes to sleep properly again, and the owner did not have to pay for painting a new part.

Job details

The BMW 6 Series (F12/F13 Gran Coupe/Cabrio/Coupe) is a refined premium car that is literally packed with complex electronics. When a car like this starts mysteriously draining its battery, it usually turns into detective work for the workshop’s auto electrician. A customer came to GT Garage with a BMW 640 (3.0 petrol, 235kw) that would no longer start after standing for a short time.

1. Electrical system diagnostics: why is the power disappearing?

Our auto electrician began an in-depth search for the parasitic drain, taking measurements at the point when the car should be in full sleep mode.

Measurement result: A constant 0.5A drain was found while the car was “asleep”. Under normal conditions this figure should be close to zero. A draw like this can completely empty even a new, powerful battery in just a few days.

2. Locating the fault: a comfort access error

After systematically checking the fuses and electronic modules, we successfully located the fault:

The fault found: A faulty comfort access (Keyless Go) handle on the passenger side.
How does it affect the car? Due to moisture or wear, the microchip inside the handle had started to malfunction and was constantly sending signals to the car’s central control unit. As a result, the car physically couldn’t “go to sleep”, keeping the electronic modules active.

3. A smart solution that cuts costs

Buying a new genuine Keyless Go handle from the dealer, then preparing and painting it, usually means a considerable outlay. At GT Garage we always try to find the most cost-effective yet technically correct solution for our customers.

Our solution: We sourced and fitted a genuine, used Keyless Go handle in exactly the colour of the customer’s car.
The benefit: This fully restored the comfort access system and gave the durability of a factory part, while completely avoiding the extra cost of painting the part.

The result

After the handle was replaced, the BMW 640’s electronics returned to factory parameters: the drain disappeared and the car now “goes to sleep” properly and safely. The customer got a fully working car with no unnecessary expense.

Photos from the workshop

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We always look for the most affordable fix that is still technically right. A used genuine handle in the car's colour saved on both the part and the paintwork.

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