Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Load-Circuit Peak Reduction
If battery discharge is detected while the engine is running (despite increased idling speed), the power supply to electrical consumer circuits are gradually reduced or completely shut off according to a table of priorities. The consumer systems concerned are divided into two groups: Priority group A and Priority group B.
| Priority Group A | Priority Group B |
|---|---|
| Rear window heater | IHKA fan (Except during defrost) |
| Headlight washing | Rear IHKA fan (E66 only) |
| All seat heaters | |
| Active seat | |
| Seat ventilation | |
| Steering wheel heater | |
| Mirror heater | |
| Windshield wiper blade heating | |
| Wet arm heating |
Priority A systems are dependent on battery SoC (State of Charge) and generator output during the operation of the consumer.
Priority B systems are only dependent on the battery SoC.
The Power Module also sends out a telegram indicating the status of the Load-circuit peak reduction function. The priority level of the message is classified by a number 0 through 6 and is as follows:
- 0 = Normal operation without peak reduction (KL 15 "ON")
- 1 = Terminal R "ON" without peak reduction OR generator defect or under-voltage acknowledged.
- 4 = Corresponds to maximum peak reduction.
- 5 = Corresponds to medium peak reduction.
- 6 = Corresponds to minimum peak reduction.
The computation by the Power Module to determine which priority level is necessary is based on the battery SoC. Example: the threshold for priority level 6 is a 65% SoC.
Current vehicle priority levels can be displayed in the Diagnosis Program.
Use the Manual With the Right Hardware
Pair factory procedures with proven DIY tools so the instructions are easier to execute.
Disclosure: Verified tool recommendations may earn an affiliate commission at no cost to you.
When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.
Rather have a pro handle this?
A certified mobile mechanic comes to your home or office. They bring the tools, you stay comfortable. No tow truck, no waiting room, no surprises.
No obligation. See pricing before you book.