Fiat 500 ECU causing misfires

Apparently this specific combination of words is used a lot in the worlds most favourite search engine Google. And we can’t blame the people for searching this, because despite being a fun little car, it’s notorious for being prone to misfires. So, are you curious what’s causing these misfires on the Fiat 500 engines? Let’s have a look at it.

Spark plugs and ignition coils

First of all a small warning: If you want your Fiat 500 to drive effortless for a longer time, use OEM parts. We know these are way more expensive, but there’s a proper reason for this: quality. The spark plugs aren’t really the problem on the Fiat 500. However, the ignition coils are prone to fail, causing misfires or one cylinder not firing up at all. And when they do fail, a lot of people choose an aftermarket coil. Pro tip: don’t fall for this. They won’t last very long.

Luckily it’s fairly easy to replace them. Both 1.2 8v and 1.4 16v engines need to have the plastic air intake removed that’s mounted on top of the engine. After this, you can exchange the ignition coils.

Fortunately the 0.9 Twinair engine is not known for having a weak ignition system. So, if you’re having ignition problems, consult an expert.


So, if a faulty ignition coil really is the problem, the car should be running perfectly again in no time. But it’s not that easy when the problem of misfiring still occurs after replacing the ignition coils. That’s mostly the first time people start to Google “Fiat 500 misfire”. In this case we advise all people to PROPERLY check all wiring and all connections. So, use a multimeter! And check the fastening tension on all connectors! (Are they clean?) Misfires often occur intermittent due to the vibration of a running engine. And therefore the source of the problem is usually a bit hard to find. You have to be really thorough. 

Back to the basics

Still no solution to your Fiat 500 causing misfires? Well, we don’t want to scare you, but this might be a good moment to check the basics. For both the 1.2 8v and the 1.4 16v engine there are plenty of examples of blown head gaskets. And if this happens, sometimes causing some coolant to leak into the cylinders, misfires will occur. So, check the compression if you’re still haven’t found the problem. Or Google “Fiat 500 ECU misfire” instead, because this is the last part that could become defective.

ECU: Magneti Marelli IAW 5SF

Ok, so here we are: ECU trouble in a Fiat 500, causing misfires. If your OBD diagnostic devices show you fault codes like P0300, P0351 or P0352, and all of the above tips didn’t solve the problem, chances are the Magneti Marelli IAW 5SF has some internal damage, causing misfires and fault codes. We strongly advise you to check the ignition signal from the ECU connector. If it’s not there, you may check the immobilizer system to rule out anything else, but the ECU may really be defective.

How to solve a problem with a Fiat 500 ECU causing misfires?

In our opinion there are only two viable options: Replace the Magneti Marelli IAW 5SF with a new original OEM device from the manufacturer or let it be repaired (remanufactured) at a specialist like ACTRONICS. This will save you a lot of money, the repaired part is plug-and-play and you’ll help the environment as well. After all, recycling is always a better option over throwing an old device away and buying a new one.

Quality guaranteed

We assure you our repair services meet the highest standards, using highly automated processes, quite like OEM manufacturing. Several years ago, we slowly but steadily moved away from the old way of repair and implemented an array of robots and machines to carry out the process. This guarantees a constant high quality, just like you’re used to with OEM parts.