Hoping this helps someone save a LOT of time and money if they have a similar issue with the MOTOR CONTROL RELAY causing very intermittent starting issues throwing a "Service EV System" fault error on the dash.
I bought a used 2020 SL+ in Dec of 2023. 40K miles. Original 12V battery.
Shortly after buying it, in Jan 2024, we had several days of subzero temps (-10 F, -15 F) here in Chicago. That's when I started have very intermittent problems with the Leaf not starting. With foot on the brake and press of the start button, the dash would show "Warning. Service EV System. Power Reduced. Stop Safely" / "No Power. Stop safely" After a couple google searches, it seemed this was likely a 12V battery issue, which seemed to fit with the issue starting when it was cold outside. Also, jumping the car worked to get it restarted. Despite the fact taht my battery voltage seemed fine via my voltmeter, every 5-6th start, the problem would return. So I bought a new 12V battery from AutoZone, and everything was fine. Except one time, on a not so cold spring night, it happened AGAIN. Luckily, my friend was around and was able to give us a jump to start the Leaf. The rest of the spring, summer, fall of 2024, all was fine.
Then this winter, Nov of 2024, the starting problem started happening all over again. But not every start. Every once in a while, every couple days, often after it hadn't been driven for several hours. I'd try to start it 5, 6, 10 times, and nothing. Then suddenly it would start after not touching or changing anything. Very frustrating. Looking back, it was the tell-tale sign of a Relay going bad.
Taking it to the dealer, they were convinced it was a battery issue and said their technician wouldn't even touch it unless we installed a Nissan battery. $375 with installation. Ouch! But they also did a "free" diagnostic and it threw no codes. And it started for them over and over. So I went home. And wouldn't you know it, the very next start, it failed! As I cursed and swore and tried to restart the car 5-10 times, it suddenly started. Of course I drove it straight back to the dealer. They kept it for 2 weeks, starting several times a day, and it never gave them a problem. So I picked it back up. And sure enough, 3 days later, it wouldn't start. And this time, even after about 50 tries starting it, it still wouldn't start, so I had it towed to the dealer.
Finally, they were able to reproduce the start failure, and identified the Motor Control Relay (M/C relay) as an issue by having multiple DTC's thrown that all led back to the M/C relay. Apparently the M/C relay is responsible for all the failed systems that showed up on their checks and I think on my LeafSpy DTC checks (see below) I tried to sleuth these myself for a bit via the 2015 manual on nicoclub.com, but it never led me to the m/c relay....
$475 more and they replaced the relay and now I have a functioning car that starts every time. Out $850 for this little relay.
I did run Leaf Spy DTCs when I was having issues, but I don't think I did it right. Pretty sure I should have cleared the DTCs after it successfully started (which I was scared to do becuase of the LeafSpy warning about clearing DTCs) and then run new DTCs when it failed to start. Instead, I had a bunch of old DTCs around that didn't help.
In the end though, the DTC for the Motor Control Relay (M/C Relay) is P31D3 which I never got.
DTCs I did get were: (maybe someone smarter than me can find one that's linked to the M/C relay in these)

View attachment IMG_2984.MOV
I bought a used 2020 SL+ in Dec of 2023. 40K miles. Original 12V battery.
Shortly after buying it, in Jan 2024, we had several days of subzero temps (-10 F, -15 F) here in Chicago. That's when I started have very intermittent problems with the Leaf not starting. With foot on the brake and press of the start button, the dash would show "Warning. Service EV System. Power Reduced. Stop Safely" / "No Power. Stop safely" After a couple google searches, it seemed this was likely a 12V battery issue, which seemed to fit with the issue starting when it was cold outside. Also, jumping the car worked to get it restarted. Despite the fact taht my battery voltage seemed fine via my voltmeter, every 5-6th start, the problem would return. So I bought a new 12V battery from AutoZone, and everything was fine. Except one time, on a not so cold spring night, it happened AGAIN. Luckily, my friend was around and was able to give us a jump to start the Leaf. The rest of the spring, summer, fall of 2024, all was fine.
Then this winter, Nov of 2024, the starting problem started happening all over again. But not every start. Every once in a while, every couple days, often after it hadn't been driven for several hours. I'd try to start it 5, 6, 10 times, and nothing. Then suddenly it would start after not touching or changing anything. Very frustrating. Looking back, it was the tell-tale sign of a Relay going bad.
Taking it to the dealer, they were convinced it was a battery issue and said their technician wouldn't even touch it unless we installed a Nissan battery. $375 with installation. Ouch! But they also did a "free" diagnostic and it threw no codes. And it started for them over and over. So I went home. And wouldn't you know it, the very next start, it failed! As I cursed and swore and tried to restart the car 5-10 times, it suddenly started. Of course I drove it straight back to the dealer. They kept it for 2 weeks, starting several times a day, and it never gave them a problem. So I picked it back up. And sure enough, 3 days later, it wouldn't start. And this time, even after about 50 tries starting it, it still wouldn't start, so I had it towed to the dealer.
Finally, they were able to reproduce the start failure, and identified the Motor Control Relay (M/C relay) as an issue by having multiple DTC's thrown that all led back to the M/C relay. Apparently the M/C relay is responsible for all the failed systems that showed up on their checks and I think on my LeafSpy DTC checks (see below) I tried to sleuth these myself for a bit via the 2015 manual on nicoclub.com, but it never led me to the m/c relay....
$475 more and they replaced the relay and now I have a functioning car that starts every time. Out $850 for this little relay.
I did run Leaf Spy DTCs when I was having issues, but I don't think I did it right. Pretty sure I should have cleared the DTCs after it successfully started (which I was scared to do becuase of the LeafSpy warning about clearing DTCs) and then run new DTCs when it failed to start. Instead, I had a bunch of old DTCs around that didn't help.
In the end though, the DTC for the Motor Control Relay (M/C Relay) is P31D3 which I never got.
DTCs I did get were: (maybe someone smarter than me can find one that's linked to the M/C relay in these)

View attachment IMG_2984.MOV