TheBradIsMAd

Shortest TLDR I could write: Had sunroof leak, fixed it. BCM started showing signs of inevitable failure a few months ago, finally died 4 weeks ago. Replaced BCM with used matching part number from matching spec car, programmed by Nissan/Infiniti Master Tech friend with Consult 3. Drove fine for 20 miles, crapped the bed again. Have checked everything I possibly can (ECU, HVAC Control Module, IPDM, All, and I mean ALL electrical connectors in BCM area, and where the battery lives) for damage or corrosion and found nothing. Car continues to throw CAN codes and drive like crap.

Full Story:

I've owned my 2013 G37 Sedan since Feb 2019 and 68k miles and up until now with 170k miles, it has been an awesome, dead reliable car. In Sep of 2023, I got my first signs of the BCM not being happy. this came about 3 days after my car began the dreaded sunroof drain failure. I promptly did the permanent fix by redirecting the lines to the AC condensation runoff which resolved that issue, but occasionally had the amber KEY light come on the cluster. And when the light was on, I'd get some strange shifting behavior. I later learned that by disconnecting any OBD2 device, the light would go away and the car would drive normal, so I ignored it and carried on.

Fast forward to Jan 27th of this year, just a few weeks ago, my friends and I were making a short 200-mile round trip to pick up a Caprice PPV for one of them, and my "Traction light", or "slip light" as some call it came on solid. I thought it was weird but the car continued to drive fine. I figured maybe a wheel speed sensor died or was unhappy so I wrote it off as a problem to solve when I got home. After we parked the car for some dinner and came back to head home, the light was off and everything seemed fine until we got about 15 minutes up i95 and the light came back, but this time with some odd trans behavior again. Unlike previous with some rough shifts when the key light came on, this brough some strange converter behavior. It was acting how the trans does when its cold outside and it hasn't reach operating temp. Basically not allowing full lock up and slipping the converter. Normally at 80mph, my car sits at around 2.5k rpms in 7th gear, but instead it was sitting at 3k. And if you gave it gas, it behaved as an unlocked or high stall converter would behave despite it being a stock stall converter. Definitely some form of limp mode.

The next day things took a turn for the worst. I'm driving home from my college church group that night, and the car goes full BMW mode. Slip light back on, TPMS light now on, Key light on, strange converter behavior, headlights coming on and off on their own, gear indicator going on and off, manual mode not working, blinkers would flash when i hit the stock but no indicator or beep on the dash. I figured it’s just the BCM that's finally done so I pick up a matching part number BCM from a local Nissan/Infiniti Salvager and contacted my Nissan/Infiniti Master Tech friend who works at a local dealer to see if he could take care of the reflash for me. Now I want to mention here because I realize I forgot to, that when I first fixed the sunroof drains, I pulled the BCM and opened it to inspect for water damage and it was clean. I work in the IT repair and refurbish field and have many water damaged computer come in weekly to my company so I know what I'm looking for when it comes to water damage or physical damage and my BCM had no evidence of either, and neither does the "new" one I have now.

It's now Feb 7th, we flash the new BCM and during the flash we got some strange behavior from the car and right after the flash as well. But we did a reset in Consult 3 after it was done, started it up, took it for a drive and everything seemed fine. I went home and, on the way, grabbed some dinner. I saw some friends across the street hanging out and slid by there and shut the car off. I come back about 20 minutes later, and go to start it and nothing. Car goes to the ON mode, but no crank, no start. I try to start it multiple times, shutting the car off, waiting and then trying again, and nothing. I decide to toss the key in the key slot and then it starts. My key battery is good so I'm a little confused but figure maybe it’s nothing. So, I finally head home, then boom. All the same lights back on the dash, weird behavior returns. So, I get home, let my friend know it crapped the bed, park it for the night and decide to deal with it later.

Next day, same lights, same behavior so I decide I’ll just drive the racecar (my 1999 Saleen S281, numbered chassis, one of 421 made, E85, MS3 standalone, 10.50 class car) for the next few days until he can come back. Of course, he has a life and work, so it takes until Feb 15th for us to get together again. In that time, he’s recommended me check all sorts of things. I pull and open up the “new” BCM again, the IPDM, the HVAC Control Module behind the radio, the ECU, and EVERY SINGLE electrical connector on the front passenger side floor board and in the battery area of the engine bay and didn’t find any form of corrosion, rust, physical damage, or anything of the sort on any of the roughly 20+ connectors and 4 modules I checked. We reflash the BCM again, not optimistic that this is the solution, but to just try it. We get no weird behavior during or after the flash like the first time, and the car is back to driving fine for exactly 26.3 miles until everything comes back again. However, I am yet to have a no start, no crank condition like before, so there’s at least progress.

Here is where both him and I are stumped. He, along with a friend at Nissan Corporate don’t believe my used BCM I bought to be bad. They think it’s a wiring issue because the car has intermittent CAN codes on the BCM, ECU, and TCM. I’m not entirely sure I’m sold on that when I’ve been yet to find any signs of water intrusion in any module, connector, or even when I cut back some of the harness tape. I’m starting to think maybe I bough a bum BCM and that we are chasing our tales. I even tried swapping the HVAC control module with a known good spare and had no improvement. The car throws a plethora of BCM codes such as P5729, B2557, B2601, B2605, B260F, U1000, but not always all of them at the same time. The TCM on and off tosses a U1000, U0100, and a P1721 (I can confirm its not the valve body as it’s a brand new OEM unit from Infiniti that’s been in the car for less than 20k miles that was installed professionally in 2023). And the ECU throws a U1001 on and off with the occasional P1212. I and multiple people are completely stumped. I really don’t know what to do. I don’t want to spend thousands at the dealer to let them dive into what could be a bottomless money pit for a car worth $8k in perfect working order, which it was in up until a few weeks ago, especially when one of the top 5 Nissan/Infiniti Techs in my region along with his corporate friend are also stumped. I guess I’m just really looking for any fresh ideas at this point. I don’t want this to be the end of the line for this car, but dailying my Saleen isn’t practical nor is it the most reliable, safe, or water tight (old vert life).

P.S. I think I’ve covered everything that’s happened in the last few weeks and everything we’ve tried. One thing I also want to mention is the limp mode still happens sometimes as well but on one occasion became a super high line pressure condition that chirped the tires every shift and wouldn’t go past 3rd gear, but I’m certain that’s because the TCM couldn’t communicate because the BCM or something in that CAN bus line is pissed so I’m kind of not going to let myself be concerned about that.

Thank you in advance for the help, and ideas. I will be watching this thread like a hawk so expect my replies to be fast lol

camopaint0707

tbh, you likely have a broken or corroded wire. I understand you saying the connectors appear fine, but i've seen this a lot. Not necessarily on infintis, but I'm person amongst my friends known for tracing wires. We had a person with a absolutely dead transmission, replaced the whole thing. Not fixed, found one broken wire inside the harness and that was it. Harness was fine, every other wire was fine. No corrosion, nothing. The wire just broke.

BULL

Based off on what you described I agree for it not to be the BCM. I do see that you are VR30 transmission and are being affected by CAN issues as well as had some TCM issues that changed your line pressure.

This makes me wonder about the work on the transmission.

TCM wiring branch being damaged from the install
Incorrect TCM placed inside the VR30 transmission
Internal wiring damage to the TCM.
The junction connector where T51 goes in TCM connector doesnt like to be disconnected and connected. Being that both CAN H and CAN L go from the bus all the way from the inside, to outside to TCM connector, to inside of transmission, to bathed in oil I would head in that direction.
TCM intermitted issue would not send the parking signal to the ECM/BCM not letting you start but allowing all other functions (reffering to that time it did not start)
BCMs can be reprogrammed so being it specifically set for your year/trim is not as critical as some folks think