BMW Charging Fault
“Your electrical machine electronics (EME) unit has failed. It will need replacing — and the total cost including parts and labour will be just over £9,500.”
That was the news Mr G received from the BMW dealership when he sought help for his 2020 BMW 5 Series 530e Plug-In Hybrid. For any driver, it’s the kind of conversation that makes your stomach drop.
Faced with such a daunting bill, Mr G was left wondering what to do next. The car’s heating and air conditioning had already stopped working, and the charging system had shut down, leaving the high-voltage battery unable to charge. With several critical systems failing, the BMW was edging closer to being undrivable.
Instead of accepting the dealership’s verdict, Mr G turned to CSN Autos in Wymondham. For us, this wasn’t the end of the road — it was the start of a challenge. And it was one we were ready to take on.
Read on to discover how our BMW specialists carried out an expert repair that brought his BMW back to life… at significantly less than the dealer had quoted.
Initial Investigation into the BMW Charging Fault
Our work started with a thorough conversation with Mr G, who gave us a clear picture of how the faults had developed, what symptoms had appeared first, what steps had already been taken, and what had already been suggested. This crucial stage ensured we didn’t just look at the car in isolation but understood the whole backstory.
From there, we connected our dealer-level diagnostic equipment to the BMW and retrieved the stored fault codes. Several codes were logged. They were:
- 21E720 – Charging electronics fault: A fault was logged showing that the connection between the charging system and its control unit was missing, which stopped the car from charging.
- 80120E – Electric A/C compressor undervoltage/overvoltage: The air conditioning compressor was shutting down because it wasn’t receiving a stable voltage within the correct range.
- 8011C4 – A/C compressor voltage sensor fault: A sensor inside the compressor was sending out incorrect signals about the high-voltage supply.
- 030ECD / 030EC1 – Charging management faults: The car’s charging system was unable to manage the charging process safely.
Together, these codes revealed a clear pattern: several high-voltage systems, the car’s charging system, PTC heater, and air conditioning, were all being affected.
Interestingly, the systems affected were all managed through the electrical machine electronics (EME) unit, the very part that the main dealership had already condemned. For us, this wasn’t a conclusion, but a pattern that pointed towards a central issue affecting electrical distribution, which would demand careful investigation.
Uncovering the Link Behind the BMW Heater Fault and Other Issues
Using wiring diagrams
Because these codes all traced back to shared high-voltage supply lines, the next step was to investigate the system in detail using BMW’s genuine wiring diagrams. These diagrams act as the car’s electrical blueprints, showing exactly how every component is connected and where voltage should be delivered.
Checking the evidence
When we reviewed the serial data from the high-voltage components, it became clear that the A/C compressor wasn’t receiving any voltage at all. That meant the issue wasn’t with the compressor itself, but with the power supply; no voltage was leaving the EME to feed the system. Wiring diagrams confirmed that the heating system, air conditioning, and charging electronics all relied on that same feed, protected by a single internal fuse inside the EME.
Applying our own test plans
To push further, we also used custom high-voltage test plans we’ve developed in-house for complex hybrid and electric vehicles. Working with high-voltage systems carries serious risk and requires specialist training and qualifications. Our technicians are fully certified to handle these systems safely, and these advanced test plans allow us to evaluate each individual component under controlled conditions and confirm whether it’s performing as it should.
Digging into the EME
Unlike the main dealership, who would have replaced the entire EME unit, we stripped the unit down and tested it at the component level. Inside, we discovered the high-voltage fuse had blown. A fuse doesn’t usually blow without reason. In most cases, it means that another part of the circuit has drawn too much current, forcing the fuse to sacrifice itself to protect the system.
Isolating the culprit
To uncover that root cause, we isolated and tested each component on the circuit in turn: the wiring harnesses, the A/C compressor, the charger, and finally the PTC heater. This was the part that stood out. Its resistance reading was far too low, meaning it was drawing more current than it should and had caused the fuse to blow. We carried out careful calculations to confirm the diagnosis.
The combination of all these forms of extra evaluation gave us a clear view of the problem. We knew it was one blown fuse that was the problem, and we could then set about fixing that directly, without a full replacement of the EME unit.
The Repair That Restored Charging and Heating
With the diagnosis complete, the priority turned to repair:
- Sourcing the fuse: A high-voltage fuse that meets the correct specifications was required, a part not available separately from BMW. Using our network, we sourced a trusted supplier. With the fuse secured, we stripped down the EME, fitted the replacement precisely to the manufacturer’s specification, and reassembled the unit correctly.
- Replacing the PTC heater: The faulty heater was removed and replaced with a high-quality component, restoring safe operation of the high-voltage circuit.
- Final testing: The system was re-tested in full using our specialist equipment, including an Insulation Resistance Tester and multimeter. With the high-voltage feed re-established, the power supply again worked as intended. Heating and air conditioning returned to normal, and the vehicle successfully charged from the mains.
The BMW Back on the Road and a Customer Relieved
With the repair complete, the difference was immediate. The BMW’s high-voltage systems powered up exactly as intended: the heating returned, the air conditioning started without issue, and the vehicle could once again charge from the mains. What had been a car on the verge of being unusable was restored to full working order.
For Mr G, the relief was enormous. Faced with the main dealership’s recommendation to replace the entire EME unit at a huge cost, he had been worried. Our work proved that it wasn’t necessary. And it wasn’t down to chance; it resulted from persistence, detailed diagnosis, and the ability to apply specialist skills to complex systems.
By combining our BMW expertise, qualifications to be allowed to work on high voltage systems, genuine wiring diagrams, and our own custom test processes, we were able to pinpoint the true fault and repair the car at component level.
The outcome was not only a BMW back in perfect running condition, but a delighted owner who saved a significant sum and gained lasting confidence in choosing a skilled independent garage over the dealership.
Why CSN Autos Is the Independent Garage of Choice
When our expert technicians were faced with this complex BMW case, we brought every part of our expertise to bear. Detailed diagnostic work which evaluates every possibility, persistence in tracing the fault, and the specialist knowledge to work at component level all came together to deliver the right outcome for the customer.
That careful process is what sets CSN Autos in Wymondham apart. We don’t just swap parts — we identify the root cause of a problem and deliver a solution that makes sense for you and your vehicle.
Here’s what you can expect when you book with us:
- Fault evaluation that saves unnecessary replacements
- Dealer-level diagnostic equipment and technical expertise
- Clear explanations and advice you can trust
- Premium quality repairs for all makes and models
- 12-month parts and labour warranty
- …And significant savings on dealer prices
We’re proud of the results: we have a {{average-rating}} star Google rating from {{review-count}} satisfied customers.
Book with CSN Autos in Wymondham today. Because your car deserves answers, not guesswork.
