Euro 6 engine charging issues — solved!

Right, I've been chasing this one for months in my van conversion. Got a 2020 Euro 6 diesel and the alternator output was all over the place — sometimes 60A, sometimes barely 40A when the engine management system kicked in.

Turned out it was the CAN-bus communication between the engine ECU and my Victron Orion-Tr Smart 12/24-500. The Euro 6 engines are paranoid about load requests and throttle back charge output if they think something's not talking to them properly.

What actually worked for me:

Swapped to a Redarc SBI12 with proper CAN integration. Cost a bit more than a basic DCDC, but the engine management finally plays ball. The charger basically tells the ECU what it's doing, and there's no conflict. Been getting steady 80-90A now instead of the erratic mess before.

I know some others have had success with the Orion just by updating firmware and tweaking voltage setpoints, so it might depend on your exact engine variant. Some Euro 6 engines are pickier than others.

Worth checking:

• Battery voltage stability (dodgy earth caused half my grief)
• Alternator output specs for your specific engine
• Whether your DCDC charger actually supports your engine's CAN protocol

Be curious if anyone else has cracked this differently — particularly interested in experiences with Fogstar or Renogy units on Euro 6 engines. Reckon there's a pattern here we haven't quite unpicked yet.

Ah, the classic Euro 6 dance. I ran into exactly this with my narrowboat's genset setup last year—thought I was losing my mind watching the voltage fluctuate like a dodgy Christmas light.

The engine management on those newer diesels is incredibly aggressive with load shedding. Mine was dropping alternator output whenever the glow plugs fired or the DPF regeneration cycled in. The fix for me was fitting a proper DC-DC charger between the alternator and leisure battery rather than relying on the van's factory charging logic.

A Victron Orion-Tr did the trick—it buffers the erratic input and actually conditions the charge. Costs a bit more upfront but saves you tearing your hair out chasing phantom electrical gremlins.

Did you check the engine fault codes? Sometimes there's a parasitic load drawing current that's telling the ECU to reduce alternator output. Worth a scan if you haven't already.

Has anyone looked at the CAN bus communication yet? Euro 6 engines are notorious for throttling alternator output based on what the engine management system thinks it needs — battery voltage, load sensing, all that.

I had similar voltage instability in my tiny house setup when I first swapped to a Victron MPPT with a smaller DC-DC charger. Turned out my alternator was getting confused signals because the battery management system wasn't talking properly to the vehicle's ECU.

Worth checking:

• Is your battery voltage stable during charging? (Mine was fluctuating between 12.8-14.2V)
• What's your earth/ground connection like? Poor earth can confuse the sensors
• Have you logged the CAN bus data to see what the engine's actually doing?

I ended up installing a separate isolator with decent capacitance smoothing and that sorted most of it. What charger are you using at the moment?

This is exactly what I've been wrestling with on my garden office setup — got a Euro 6 unit powering the battery bank and the voltage regulation is a nightmare.

@Liz1979's spot on about the CAN bus. Have you checked whether your alternator's actually compatible with the engine's native control system, or are you using a standalone regulator? I switched to a Victron Orion-Tr 48/16 DC-DC charger specifically because it ignores the engine's mood swings and just takes whatever amperage it can get cleanly.

The other thing worth testing — what's your actual load demand when the alternator's throttling back? Mine was doing the same thing until I realised the engine management was protecting itself because the battery wasn't accepting charge fast enough. Sorted itself once I upgraded the battery clamps and checked the cabling.

What alternator have you got fitted? Some of the OEM Euro 6 units are notoriously conservative with their output curves.

Mate, if your Euro 6 is doing the alternator limbo dance, check whether your DC-DC charger is actually talking to the engine management system or just guessing. Mine was throwing a right wobbler until I realised it needed proper CAN bus integration—turns out the ECU was actively suppressing output thinking the battery was full, even when it was sat at 70%.

Swapped to a Victron Orion-Tr with proper automotive sensing and it's been rock solid since. Worth verifying your charger's actually handshaking with the engine rather than just reading raw voltage, because Euro 6 engines are basically paranoid teenagers—they need constant reassurance they're not about to blow up the electrics.

What charger are you running currently?

Yeah, the CAN bus throttling is a proper nightmare with Euro 6. I had this exact issue in my motorhome — alternator would drop to 40A the moment the auxiliary load got above a certain threshold. Engine management system thinks it's protecting itself.

The thing that actually sorted mine was an isolator relay on the alternator sense wire. Stops the ECU from seeing the charger's demand and clamping output. Some folks use a Victron Orion-Tr Smart DC-DC which has configurable charge profiles, but honestly the relay approach is simpler and cheaper.

Worth checking your alternator spec too — 2020 Euro 6 diesels often come with undersized alternators anyway (110A-150A max). If you're trying to push serious charge current through a DC-DC, the engine's just saying "nah, not happening."

@QuietMaker — what capacity are you aiming for on the charge current? And is your engine management kicking in at idle or under load? That'll narrow down whether it's a protection strategy or just a limitation of the alternator itself.

The CAN bus throttling is definitely the culprit here. Euro 6 engines are paranoid about thermal management and will deliberately starve the alternator if they think they're getting too hot or the battery's already charged.

What sorted mine was installing a Victron DC-DC charger (the Orion-Tr Smart) rather than relying on the vehicle's native charging logic. It essentially bypasses the engine's decision-making and manages the charge profile independently. Cost a fair bit but the stability is night and day — now pulls consistent 80A regardless of what the engine management thinks.

Worth checking your alternator's CAN configuration too. Some units have a programmable "smart output" mode that you can adjust through the OBD port, though you'll likely need dealer software or a specialist.

If you're dead-set on sticking with stock charging, make sure your battery bank isn't sending voltage feedback that's confusing the ECU. A cheap multimeter check between alternator output and battery terminal can show if there's a voltage drop that's triggering the throttle.

What charger are you currently using? That'll help narrow down

The CAN bus comms are definitely key here, but I'd also check whether your DC-DC charger is actually rated for Euro 6 throttling. I'm running a Victron Orion-Tr Smart 12/24-16 in my static caravan setup (separate diesel gen, not a van engine) and the difference between a charger that listens to the engine management system and one that just hammers the alternator is night and day.

What charger are you using? Some of the cheaper units don't negotiate properly with modern ECUs — they just pull whatever they can get, which makes the engine clamp down harder. Worth checking if yours has CAN integration or at least proper load-sensing.

Also, are you seeing the drop happen at specific RPM ranges? Euro 6 diesels often get aggressive with alternator output around 1500–2000 RPM to manage EGR temperatures. If your charger's pulling too hard in that sweet spot, the ECU will throttle it back ruthlessly.

How long have you been running this setup? Sometimes the issue sorts itself once the charger and engine learn each other

This thread's hitting on something I wrestled with in my own motorhome conversion last year. The CAN bus throttling is definitely part of it, but I found the real game-changer was upgrading to a Victron Orion-Tr Smart 48/16 that's explicitly Euro 6 compatible.

What @WhatsAFuse65 and @WattAndrea are spot on about — the engine management system genuinely believes it's protecting itself. But here's the bit that caught me out: my old DCDC wasn't actually communicating back to the engine ECU to say "mate, I'm not maxing you out, chill."

The Victron handles that handshake properly. Once that was in place, my alternator settled into a predictable 80-90A charge window instead of the erratic dancing I was getting before.

Worth checking your charger's spec sheet specifically mentions Euro 6 CAN protocol support. Some older units just don't speak the language, and the engine gets paranoid about thermal load.

@BayJason's got it exactly right — it's not just about the

Yeah, the CAN bus throttling is annoying but there's a practical workaround. Have you isolated the DC-DC charger from the engine's CAN network? Some units like the Victron Orion-Tr Smart handle it fine, but cheaper alternatives don't always.

What I did with mine was run a dedicated alternator on a second belt (bit more complex but bulletproof). Alternatively, fit a manual isolator switch between the alternator and DC-DC so you can bypass the smart charging when stationary and just bulk-charge from the engine at full tilt.

Also worth checking: is your alternator actually Euro 6 spec? Some older units weren't, and they'll throttle harder. And confirm the DC-DC charger's firmware is updated — Victron releases patches for this exact issue.

What charger are you running? That'll make a difference to the solution.

The CAN bus throttling on Euro 6 engines is a proper headache — been there with my boat's auxiliary charging setup. What @Wez1961 mentioned about isolation is spot on, but I'd add that you need to be careful not to confuse throttling with actual alternator regulation issues.

Check your DC-DC charger's input voltage ripple first. I found mine was oscillating wildly because the alternator's internal regulator was fighting the charger's demand. Swapped to a Victron Orion-Tr 48/16 with input filtering and it sorted it completely.

The other thing nobody mentions — make sure your engine's battery sense wire isn't being used for CAN communications. Some Euro 6 setups (particularly Bosch systems) piggyback diagnostic data on that line, which confuses aftermarket chargers.

What charger are you running? And is the van's OEM system trying to manage charge differently when you're stationary? That can be the real culprit rather than the CAN bus itself.

Interesting thread this. Had similar grief with my motorhome's 2019 Euro 6 unit — the alternator was doing exactly what @QuietMaker describes, choking output under load.

Before you go down the isolation route that @Wez1961 mentions, have you checked what your DC-DC charger's actually seeing on the CAN bus? Mine turned out to be receiving conflicting load signals from the engine management system. The workaround that finally worked was swapping to a Victron Orion-Tr Smart with the right firmware version — it's got better filtering for those noise spikes Euro 6 systems chuck out.

Also worth verifying your alternator's actually rated for continuous high output. Some OEM units on those engines are gimped deliberately for emissions compliance. If yours is undersized, no amount of tweaking the charger will fix it — you might need an uprated replacement.

One thing nobody's mentioned yet: what's your battery spec? If you've got undersized cables or a weak leisure battery, the DC-DC charger will throttle itself down trying to protect the circuit. Worth measuring actual voltage at the

Cheers for sharing this, @QuietMaker. Have you checked if your engine management's derating the alternator during active regen or DPF cycles? That's often the culprit. Also worth verifying your alternator's CAN termination resistor isn't faulty — seen a few dodgy units cause erratic output. What's your current DC-DC setup handling the voltage variation?

The CAN bus throttling @Davo24 mentions is definitely the culprit here. Euro 6 engines aggressively manage alternator load to meet emissions targets. I'd recommend isolating the charging circuit with a dedicated DC-DC converter — Victron or Renogy units with configurable input limits work well. This bypasses the engine management entirely and gives you consistent output. What's your current battery setup handling?