Intermittent start failure 2020 Leaf Service EV System error - SOLVED - faulty Motor Control Relay

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ev4life

Member
Joined
May 5, 2013
Messages
19
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)
1736906915053.jpeg

View attachment IMG_2984.MOV
 
Thank you this is exactly what I've been experiencing - need to take it to the dealer again on this issue!
Why not just buy the relay ( a few $ ) & change it, just pulls out ( you may need to push or pull a plastic tab or 2 ) then new one plugs in.
Plug & play.

Part No is in this post :- https://mynissanleaf.com/threads/m-c-2523079917-relay-multiple-failures.37139/
Part No 2523079917.

Available from Amazon :- https://www.amazon.com/s?k=nissan+leaf+2523079917&crid=11OEUIG2Y71RO&sprefix=nissan+leaf+2523079917,aps,194&ref=nb_sb_noss

Or your local Nissan dealer.

Located in the car in this document :- https://fuseandrelay.com/nissan/leaf.html

FUSE BOX 3 under the bonnet, relay G.
 
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Why not just buy the relay ( a few $ ) & change it, just pulls out ( you may need to push or pull a plastic tab or 2 ) then new one plugs in.
Plug & play.

Part No is in this post :- https://mynissanleaf.com/threads/m-c-2523079917-relay-multiple-failures.37139/
Part No 2523079917.

Available from Amazon :- https://www.amazon.com/s?k=nissan+leaf+2523079917&crid=11OEUIG2Y71RO&sprefix=nissan+leaf+2523079917,aps,194&ref=nb_sb_noss

Or your local Nissan dealer.

Located in the car in this document :- https://fuseandrelay.com/nissan/leaf.html

FUSE BOX 3 under the bonnet, relay G.
Why not just buy the relay ( a few $ ) & change it, just pulls out ( you may need to push or pull a plastic tab or 2 ) then new one plugs in.
Plug & play.

Part No is in this post :- https://mynissanleaf.com/threads/m-c-2523079917-relay-multiple-failures.37139/
Part No 2523079917.

Available from Amazon :- https://www.amazon.com/s?k=nissan+leaf+2523079917&crid=11OEUIG2Y71RO&sprefix=nissan+leaf+2523079917,aps,194&ref=nb_sb_noss

Or your local Nissan dealer.

Located in the car in this document :- https://fuseandrelay.com/nissan/leaf.html

FUSE BOX 3 under the bonnet, relay G.
The part number you quote is for something else and not the M/C relay, from my searching anyways. Also can't see where it is located from your posts
 
Update Feb. 6, 2024 Yes, the motor control relay seems to have fixed my issue - third visit to dealer.

My intermittent start problem was not solved by replacing the battery with the higher CA/CCA battery from Canadian Tire. Last Thursday my car would not start again all morning. An afternoon snow storm loomed, requiring that I move the car off the street for city snow clearing. I was ready to call for another tow to the dealer but gave it one more try - it started! So I drove through early rush hour traffic in a snow storm to get it to the dealer. The EV tech wasn’t coming in til Monday. The service advisor at the desk, at my request, tried starting it the next morning and finally had the experience himself that it would not go into ready mode.


Monday they checked codes, fully charged both batteries, test drove and found no problems, no codes. Fortunately the tech volunteered to take the vehicle home himself and try it again in the morning, and it would not go into ready mode again. Temperature was -10 C.


Finally their Techline suggested replacing the motor control relay “due to previous cases with similar concerns”. Repair done, codes cleared, he took it home again the next night, and the car worked fine in the morning (temperature -17 C). When picking it up today, I asked whom I could write a letter of complaint to, that I twice in the previous few weeks paid for diagnostics without getting a solution. The supervisor? immediately offered to refund one of those fees on the spot! We’ve made 4 short trips since and it started every time. What a relief!


Sure hope this fix holds good.


Part number 2523079927 comes up as “tow hitch harness relay”, which makes me wonder if the fact that the previous owner installed a tow hitch 2 years ago had anything to do with this problem developing? He had “battery dead” warning lights com on a year later, and replaced the OEM battery then (Sept. 2023)
 
Looks like something we may have to watch for, esp if it doesn't "throw a code".
If I understand the symptoms, they are: random no start, mostly when cold/cold soak, no codes set. Does this sound correct?
However that part number didn't come up, if the last two digits are xxxx17 it does come up as tow relay.

Even direct from Nissan parts it is under $10, so a hell of a lot cheaper than a 12 volt battery!
My guess is: the coil resistance is in spec, but the relay arm will not pull in when cold, so the "system" doesn't detect a "fault" like an open on the coil, so no code set.
It is hard to find good automotive diagnosticians, and even more so for EV's.
I loath throwing parts at something to try and "get lucky",However sometimes with intermittent problems like this, it is the best you can do, if you can't make it malfunction at will.
A $10 relay is a better bet than a $150+ battery, that can be charged and tested before being replaced.
 
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Why not just buy the relay ( a few $ ) & change it, just pulls out ( you may need to push or pull a plastic tab or 2 ) then new one plugs in.
Plug & play.

Part No is in this post :- https://mynissanleaf.com/threads/m-c-2523079917-relay-multiple-failures.37139/
Part No 2523079917.

Available from Amazon :- https://www.amazon.com/s?k=nissan+leaf+2523079917&crid=11OEUIG2Y71RO&sprefix=nissan+leaf+2523079917,aps,194&ref=nb_sb_noss

Or your local Nissan dealer.

Located in the car in this document :- https://fuseandrelay.com/nissan/leaf.html

FUSE BOX 3 under the bonnet, relay G.
That’s exactly why I made this post. Hopefully this will help someone jump to at least trying an easy cheap(er) fix than the whole process I went through. The problem was we didn’t know it was the relay because it was so hard to “catch” the intermittent problem with a diagnostic. And even then it was via deduction.
 
Looks like something we may have to watch for, esp if it doesn't "throw a code".
If I understand the symptoms, they are: random no start, mostly when cold/cold soak, no codes set. Does this sound correct?
However that part number didn't come up, if the last two digits are xxxx17 it does come up as tow relay.

Even direct from Nissan parts it is under $10, so a hell of a lot cheaper than a 12 volt battery!
My guess is: the coil resistance is in spec, but the relay arm will not pull in when cold, so the "system" doesn't detect a "fault" like an open on the coil, so no code set.
It is hard to find good automotive diagnosticians, and even more so for EV's.
I loath throwing parts at something to try and "get lucky",However sometimes with intermittent problems like this, it is the best you can do, if you can't make it malfunction at will.
A $10 relay is a better bet than a $150+ battery, that can be charged and tested before being replaced.
Well said.
Looking back, how would one decide which part to throw at this problem without having the codes that pointed to the specific relay? I’m more of a try it and see guy myself, so it still burns me I didn’t at least try SOMETHING to fix this, but I really didn’t know where to start even after following the codes in the manual.
Any guidance appreciated to improve my logic and sleuthing for the NEXT thing that goes wrong! lol
 
Well said.
Looking back, how would one decide which part to throw at this problem without having the codes that pointed to the specific relay? I’m more of a try it and see guy myself, so it still burns me I didn’t at least try SOMETHING to fix this, but I really didn’t know where to start even after following the codes in the manual.
Any guidance appreciated to improve my logic and sleuthing for the NEXT thing that goes wrong! lol
This is one, where the experience of someone on the board, finely getting it resolved then posting the solution makes it possible for others.
To diagnose, you would have to have the malfunction then trace out where has power, where it does not, and locate the point where the problem is.
Contrary to popular belief, most DTC's only point to the system that has a problem, and not the specific item that is faulty .
In this case, part of the cars system is not powering on, and that throws com codes, where the BCM is expecting inputs it is not receiving, it can only tell you it hasn't received communication from some items and those items appear "dead".
In your case you see a lot of brake and sonar codes and a whole bunch of EV battery system codes, and even HVAC codes.
In reality none of those system are bad, they are just not getting power to "wake up".
One could check out each individual system to find they all have a power issue, or you could take a chance on at $10 relay.
The 1st person to resolve the problem, had a lot to do or had a lot of wiring diagrams out in front of them to look for the common place all these items come together.
given that it is an "intermittent problem" it can be deceiving, you may think you have got to the bottom of the problem, only to find it "just decided to work".
There are thing like "Idenifix"where mechanic's post solutions to problems they run across, basically a "common brain trust" but they are subscription, and also require enough mechanic's to have run across the problem and post their solution, not all solutions turn out to fix all problems, but if 85% or more post that it worked for them, it is a good bet.
EV's just haven't been around long enough to know where all the weak points are.
 
Intermittent electrical problems are most commonly due to wiring harness damage, corrosion in connector contacts, or any sliding or make/break electrical contacts.

For troubleshooting, rule these out thru inspection or replacement.

Relay contacts can be damaged by arcing that occurs when opening under load, resulting in welded contacts, or frosted precious metal contact surfaces that no longer conduct.

Hard lessons learned the hard way.
 
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