Unknown PCM Error/ Battery Light

[alexia.x]

Hey everyone,

I have a 2018 GT2 with about 30,000 miles on it and for about the last year and two months (since installing the JB4 in June of 2021), I've had the battery light on my dashboard nonstop. I went through some troubleshooting with BMS to replace the circuit board and OBDII connectors on the JB4 in hopes of it being fixed, but the light was still on and the code was unreadable. The car has been driving perfectly fine the whole time, no issues except for mild overboost which was fixed by installing a TiAL Q BOV/mishimoto adapter. I've had the dealership test my battery many times throughout that period of time and they said it was perfectly fine and they also swapped out my alternator two months ago under warranty as a precautionary measure but the light was still on. They tried to scan the code to see what the issue is many times but with no luck because no actual code is showing. The JB4 hasn't been able to pick it up either- it shows my car has no codes. The dealership ultimately said it has to do with my car's PCM and advised that I drive the car for a few thousand miles after swapping the alternator to see if they can get some sort of fix figured out to where it's covered under warranty but they're not sure what that fix would be yet.

Not sure if anyone's experienced anything like this or has any advice on how to continue, especially considering the car has been driving normal for all of this time? Not sure if this is an issue with the turbos or electronic module communication or the jb4, etc.

 

[KyleSC]

I have the same problem and I'm looking for a fix. It showed up after the battery drained while working on the jb4 with the ignition on. I scanned and had some voltage codes relating to alternator and solenoid for recirculator. The codes cleared, but the light is still on. After I jumped the battery I drove it and it was jerking and sputtering. Clearing the codes made it drivable, but nothing else after clearing the codes. The OBD app I used for a long time wouldn't connect anymore. It drops after connecting to the adapter and repeats. I switched to TorquePro and it works fine. Are you having any of these issues? Let me know if you find a fix and I'll do the same.

 

[alexia.x]

I have the same problem and I'm looking for a fix. It showed up after the battery drained while working on the jb4 with the ignition on. I scanned and had some voltage codes relating to alternator and solenoid for recirculator. The codes cleared, but the light is still on. After I jumped the battery I drove it and it was jerking and sputtering. Clearing the codes made it drivable, but nothing else after clearing the codes. The OBD app I used for a long time wouldn't connect anymore. It drops after connecting to the adapter and repeats. I switched to TorquePro and it works fine. Are you having any of these issues? Let me know if you find a fix and I'll do the same.

I haven’t had any of these issues but they seems to fall under the same electrical umbrella, I’m jealous that yours read the codes! I tried to reach out to JB4 customer service plenty of times but they haven’t been much help and told me that their product wasn’t the issue.

Side note on the performance of the JB4, I got my logs looked at by a local professional ECU/TCU tuner and they said they don’t look great, lots of overboost/lag issues (that BMS said can only be fixed with their ewg connectors, though the tuner helped fix it with a Tial Q BOV & mishimoto single BOV adapter). I’ve been pretty underwhelmed with the product- it’s a good piggyback for a beginner build but I definitely think there’s safer options out there. I’m glad the TorquePro worked out for you, I’ll have to look into that!!

 

[rpoffen]

I haven’t had any of these issues but they seems to fall under the same electrical umbrella, I’m jealous that yours read the codes! I tried to reach out to JB4 customer service plenty of times but they haven’t been much help and told me that their product wasn’t the issue.

Side note on the performance of the JB4, I got my logs looked at by a local professional ECU/TCU tuner and they said they don’t look great, lots of overboost/lag issues (that BMS said can only be fixed with their ewg connectors, though the tuner helped fix it with a Tial Q BOV & mishimoto single BOV adapter). I’ve been pretty underwhelmed with the product- it’s a good piggyback for a beginner build but I definitely think there’s safer options out there. I’m glad the TorquePro worked out for you, I’ll have to look into that!!

I'm surprised you are having JB4 issues. Kind of all depends on what maps and fuel you are using.
It didn't really wake up that much until I started mixing to E30 and using map 4, huge difference.

 

[alexia.x]

I'm surprised you are having JB4 issues. Kind of all depends on what maps and fuel you are using.
It didn't really wake up that much until I started mixing to E30 and using map 4, huge difference.

Me too I was disappointed, I can’t drive in Map2+ without going limp even with a decent amount of bolt-on’s. I use 91 from Chevron/Shell (no 93 in my state unfortunately) so I’m hoping the performance will get better once I get a WMI kit. Seems like running E is what really kicks off performance

 

[rpoffen]

Me too I was disappointed, I can’t drive in Map2+ without going limp even with a decent amount of bolt-on’s. I use 91 from Chevron/Shell (no 93 in my state unfortunately) so I’m hoping the performance will get better once I get a WMI kit. Seems like running E is what really kicks off performance

I'm in California, so 91 is the highest. When I would go to the track (Sacramento Raceway Park), I could mix E85 to get E30 (I have a fuel-it flex fuel sensor), and run map 4, with no timing corrections. Took me down to about 12.2 in the 1/4. I since put in the WMI kit, just running the 91 with boost juice and my best time is 11.80 in the 1/4.

 

[alexia.x]

I'm in California, so 91 is the highest. When I would go to the track (Sacramento Raceway Park), I could mix E85 to get E30 (I have a fuel-it flex fuel sensor), and run map 4, with no timing corrections. Took me down to about 12.2 in the 1/4. I since put in the WMI kit, just running the 91 with boost juice and my best time is 11.80 in the 1/4.

That’s impressive! WMI is definitely the way to go on the west coast

 

[rpoffen]

That’s impressive! WMI is definitely the way to go on the west coast

Where are you that also doesn't have 93?

 

[alexia.x]

Where are you that also doesn't have 93?

I’m in Phx AZ

 

[rpoffen]

I’m in Phx AZ

Huh, I figured that Cali was about the only place that didn't offer 93.
Oh well, once you get WMI, doesn't matter.
For me, now that winter is here, and no more Wednesday night drags at Sacramento Raceway till next spring, I keep it on map 1. Comes the time, I just set map 7 and WMI is ready to go.