Audi 48V alternator repair (A6, A7, A8, Q7, Q8)

The MHEV's main positive difference – a 48-volt power system designed to be simpler and cheaper than the high-voltage equipment of familiar hybrids. While the developers have succeeded in achieving their goal, mild hybrids do have weaknesses. The unit that most frequently requires repair – the Audi alternator.

What an alternator is and how it differs from a conventional one

One of the main manufacturers of cars with the Mild Hybrid system is the Audi brand. Mild hybrids can be not only petrol but also diesel cars, which makes them even more economical. The operating principle of the MHEV evolved from the «start-stop» system. The engine doesn't actually idle; in traffic jams and at traffic lights it is switched off and then restarted, but with the help of a 48V starter generator.

The same unit helps the engine in emergencies (sudden acceleration, uphill climb) and charges the 48-volt battery in the rear of the car. At the same time, a conventional 12 V starter is present in parallel: it starts the internal combustion engine if the oil temperature is below 45oC. Due to its presence (and connection with the flywheel), the connection of 48-volt starter-generator in Audi cars is realised by belt transmission, like other attachments. This is more convenient for integration into existing engines.

The 48V &ndash generator is a three-phase alternating current (AC) motor with an integrated 12V inverter to supply the on-board mains. The starter-generator is linked to the engine ECU via its own CAN bus and controls the pump (coolant pump) itself, as it is water-cooled.

The starter-generator is a water-cooled motor.

In addition to Audi, several other brands have a similar 48-system with similar characteristics

• Renault (Grand Scenic, Austral)
• Jeep (Wrangler, Avenger and others)
• Dodge (RAM)

In the vast majority of cases, the manufacturer of 48V alternators is Continental. However, their parameters differ, first of all, it concerns the amperage delivered by the device. 

The most common faults of 48-volt starter generators

Starter-generator problems are quite common in cars. The first recalls of Audi cars due to this unit in Europe date back to as early as 2020. But while dealers replaced it free of charge then, those who later experienced the «mild-hybrid disaster» as it was dubbed in the media, had to pay the cost of replacing the Audi alternator out of their own pockets.

The Audi starter-generator has been recalled in Europe since 2020.

The driver learns about the faults from the messages on the dashboard. But you should bear in mind that these will not tell you that the alternator has broken down, but that there are more general faults in systems such as:

The alternator is not the only thing that's broken down.

1. The mains
2. Start-Stop system
3. Brake power booster and other certain components connected directly to the starter-generator or 48-volt battery

Further details can be obtained from the error information available to the diagnostic equipment. The most common errors that the ECU generates in the event of 48-volt system failures are:

• P065C00 Alternator mechanical characteristics - Intermittent operation

Also available:

• U046900 Starter generator control unit, 36564 invalid signal
• P0CA700 Hybrid drive battery, discharge current too high
• U046900 Starter/generator control unit, invalid signal

The most common problems are caused by electrical boards and contacts in the alternator processors breaking down. While Audi officially cited moisture as the cause of some of the recalls, the real cause was different. The operating current was too high, causing the power transistors to heat up and the power board to blow out.

A car in most cases stops showing signs of life, i.e. immobilises, because the alternator, when it fails, completely drains the 48-volt battery and the battery goes into protection. Even installing a new alternator doesn't solve the problem: first you had to remove the protection with ODIS. In addition, the discharge of the high-voltage battery threatened it with irreparable processes – destruction of cells. In addition, in most cases, the car stops showing «signs of life» i.e. it becomes immobilised.

How much does it cost to replace or repair a 48V starter generator on an Audi

Frankly, car (VAG) and appliance (Continental) manufacturers have given little thought to the repairability of these units. Repairing an Audi alternator is difficult even for qualified specialists. The high-tech product consists of complex electronic components: microcontrollers, electronic boards and other equipment. In addition, 48 V is considered dangerous to human life.

Therefore, do not attempt repairs yourself without the proper skills and qualifications. Nor should you be in a hurry to give your 48V generator to a dubious organisation, as it often loses the function of the starter after such a botched repair. It is advisable to go to a reliable company that has extensive repair experience and an exchange fund of repaired units.

So you should not be in a hurry to give your 48V alternator to a dodgy organisation.

STS Parts offers remanufactured starter generators for various Audi models at the following prices:

The client receives a fully restored to factory parameters (and to some extent exceeding them) workable unit, which is covered by a warranty. Since Audi has learnt to treat «childhood diseases» of its starter-generator by re-flashing it to the required parameters, we eliminate the factory defects made in the first versions of the starter-generator. We fill it with firmware, which already lowers the current produced by the generator, which ensures its further trouble-free operation.

As you can see, this is much more favourable than the cost of replacing an Audi alternator, which is about 2000 euros (more than 8500 zł at the current exchange rate).