EV Hybrid Service/Services
The DC-DC converter and the on-board charger
A hybrid or an electric car has no alternator. The 12 V battery is charged by the DC-DC converter, from the high-voltage battery. When the converter fails, the small battery goes flat, warning lights come on and the car may refuse to start. We check the converter and, where relevant, the on-board charger before replacing anything.
When the converter or charger needs checking
It is worth coming in when the 12 V battery won’t hold, there are faults on the converter or on-board charger, and replacing the small battery again and again doesn’t solve anything. We use measurements to separate the converter, the charger, the wiring and the 12 V battery.
The 12 V battery keeps going flat, even though it is new
If the small battery drains again and again, the cause may be the DC-DC converter no longer charging it. A new battery without checking the converter is money spent with no result.
Several warning lights, the car won’t go into READY
The car’s control units, ABS or hybrid system can throw faults when the 12 V voltage drops. We measure the voltage at rest and under load, not just read an isolated code.
Charging from the socket is slow, stops or shows an error
On plug-in hybrids and electric cars, the on-board charger (OBC) turns the alternating current from the socket into direct current for the battery. We check the supply, the communication and whether the fault is in the charger, the port or the cable.
A smell, noise or heat from the power unit
The converter and charger handle high power. Signs of overheating or coolant leaks need checking before the fault spreads.
Why we check the converter and the charger together
On many hybrids and electric cars, the DC-DC converter and the on-board charger share their supply, cooling or communication, and on some models they are even in the same unit. A 12 V problem can hide a charging problem, and vice versa.
The 12 V battery depends on the converter
The small battery powers up the control units and relays that bring the car to life. After that, the whole 12 V system is supplied by the converter. Without it, the battery goes flat within a few dozen minutes of driving.
On some models they share a box
On the Hyundai Ioniq 5, Ioniq 6, Kia EV6 and some Genesis models, the charger and converter form a single unit, the ICCU. Its faults led in 2024 to the recall of more than 200,000 cars: the 12 V battery stopped charging and the car gradually lost power.
Parts replaced by guesswork are expensive
Power units are expensive. We tell you what we have confirmed by measurement and what we can’t check, before you order any part.
How we work, step by step
We start from the 12 V or charging symptom, read the codes, measure the voltages and communication, then fix the confirmed cause.
1. You tell us what is happening
Whether the 12 V battery drains, whether charging from the socket fails, or what errors you have seen. From that we decide whether to start with the converter, the charger or both.
2. We read the codes and measure the voltages
We read the relevant codes and measure the 12 V battery voltage with the car off, with the ignition on and with the car running. With the car in READY, the converter should supply around 14 V; if it doesn’t, we look for why.
3. We check the on-board charger, where relevant
On plug-in hybrids and electric cars we test charging, communication with the charging station or socket, and the charger’s signals. We separate the port, the cable and the unit.
4. We fix the confirmed cause
We repair or replace the faulty part, or fix the wiring or cooling problem, based on the measurements. We don’t replace the converter or charger on a hunch.
5. Final test and handover
We check the 12 V voltage again and, where relevant, charging, clear the codes and explain what we measured and what we replaced.
What converter and charger work includes
The details depend on the model and the symptom. As a rule, the check includes:
- Diagnosis of the DC-DC converter and the 12 V system
- Measuring the 12 V battery voltage at rest and with the car running
- Checking the converter’s supply from the high-voltage battery
- Reading on-board charger faults and charging communication, where relevant
- Visual inspection of connectors, wiring and hot spots
- Checking the cooling of the power units, where accessible
- Checking the recalls that apply to your model
- Fixing the confirmed cause, a final test and a warranty on the work
What we often find
We will publish real, documented jobs one by one. Until then, here are situations we come across often:
Hybrids
A new 12 V battery that still goes flat
The converter no longer charges the small battery when loads are switched on. A new battery hides the fault for a few days, then the problem returns. Measuring the converter settles it.
Plug-in hybrids and electric cars
Charging from the socket fails
The on-board charger shows communication or supply errors. Sometimes the port or cable is to blame, sometimes the unit. We separate them by testing, not by replacing parts one after another.
What the work covers and what it doesn’t
The warranty covers the work on the converter, the charger or the confirmed cause, under the conditions on the handover sheet. It doesn’t cover wear of the 12 V battery or faults unrelated to our work.
A warranty on what we did
You get in writing what we replaced or repaired, what we measured and for how long we guarantee it.
Limits stated from the start
If the fault only appears now and then or needs major dismantling, we tell you from the start. We don’t give firm verdicts without data.
If the problem is elsewhere
If the wiring, the port, the charging station or the high-voltage battery is to blame, we tell you and suggest the right step. The converter is replaced only if the measurements show it.
Frequently asked questions about the DC-DC converter and on-board charger
What does the DC-DC converter do on a hybrid or electric car?+
It steps the high-voltage battery down to around 14 V to supply the 12 V system and charge the small battery. It does the job of the alternator on a conventional car.
Why does the 12 V battery keep failing?+
Often it isn’t the battery’s fault but the converter’s, which no longer charges it properly. If you replace the battery again and again without checking the converter, you are treating the symptom, not the cause.
Is the on-board charger the same as the DC-DC converter?+
No. The on-board charger (OBC) charges the high-voltage battery from the socket. The DC-DC converter supplies the 12 V system from the high-voltage battery. On some models, such as the Hyundai Ioniq 5 and Kia EV6, they are in the same unit; on others they are separate.
I have an Ioniq 5 or EV6 and the 12 V battery keeps going flat. What should I do?+
First check whether the car has an open recall for the ICCU unit. Hyundai and Kia fix it free of charge at a dealer. If the recall has already been done and the problem persists, we can help with the diagnosis.
How long does the diagnosis take?+
It varies from case to case, depending on the symptom and the model. We give you an estimate after the measurements.
Could my home charging station be to blame rather than the car?+
Yes, when charging from the socket fails. We check the communication on the car as well as the station’s usual signals. If the station looks to be at fault, we tell you.
Check the 12 V system and charging
Book a diagnostic check. We tell you whether the problem is the DC-DC converter, the on-board charger or something else, before you replace the wrong part.
Book a diagnostic check