TCU Disconnect Service

[Lothsahn]

For anyone wanting to have their 2G TCU disconnected (for security reasons), you should know the following:
1) I had the service performed at 3 separate dealerships, and none of them could get it right. Keep in mind that I'm in the midwest (not CA), so their experience with Leafs is very limited. The dealerships all made the same mistake--they assumed that because there was no 2G service, the TCU was disconnected. In reality, AT&T no longer has 2G service, so the TCU was still active.

2) Disabling the TCU (even if done properly) does NOT disable the nag screen on the 2011/2012 cars. Even with no TCU, the car still asks you to accept sending carwings data--and no fix. Thanks Nissan. If anyone knows a way around this, please let me know.

3) If the TCU is disabled and the car's 12V battery is disconnected for >5 minutes, the carwings unit ID information screen will show 4 asterisks for the following items: TCU ID, TCU Phone No, SIM ID, and VIN. If any of those show values in them, then the TCU is still powered and connected to the car.

4) If you have a US TCU and you want to disconnect it, it's probably honestly easier to just do it yourself. Note: The Japanese TCU appears to be in a different location, and I have no idea where the EU TCU is.

The only tool you'll need is a #2 phillips screwdriver.

Steps to disconnect the TCU:
1) Remove the 12V battery black terminal so the car doesn't have power
2) Remove the glovebox as shown in this video: https://www.youtube.com/watch?v=YHIWHPpg_rY
3) After removing the glovebox, the TCU (at least for my 2011 leaf) is on the right side of the glovebox opening. It's attached to a metal frame held in by two screws. Remove the two screws so you can get to the plugs on the TCU.
4) There will be three plugs: A grey plug with many wires, a white plug (wide with most wires missing), and a blue plug with 1 wire. You want to disconnect the grey plug only, which will remove power to the TCU.
Note: The blue plug is for the antenna. Disconnecting the white plug caused a number of CAN bus DTC's. With the grey plug disconnected you will get one TCU code (U1A05 000B TCU USB Comm AV-199) which you'll need to ignore.
5) Recommended: Replace the cabin air filter while you have the glovebox out.
6) Put the glovebox back in

Honestly, it took me 15 minutes to fix, and I replaced the cabin air filter while I was in there. It was super simple and I wish I had just done it originally. It would have saved me hours driving to the dealership, dropping off the car, and waiting for them to (not) perform the service. It doesn't put any warning lights on the dashboard.

I only have the 2G TCU, so I can't confirm for the 3G TCU, but doing this will most likely resolve any 12V battery drain issues for that TCU as well--at the cost of having no carwings.

 

[TheLostPetrol]

Steps to disconnect the TCU:
1) Remove the 12V battery black terminal so the car doesn't have power.

Would disconnecting the red terminal work just as well?

 

[WoodDancer]

Yes you could, but don't disconnect the red terminal.

The black terminal is grounded to the car. If the wrench slips while disconnecting the terminal, not a problem.

If you disconnect the red terminal with the black terminal connected and the wrench touches the frame or other grounded metal, you have shorted the battery. That is, you may have a
-wrench too hot to hold
-wrench welded to the metal where it touched
-dead battery
-wish you disconnected the black terminal

 

[nateads]

I tried to reverse this idea to see if I could get my carwings back up after the 2G deactivation but it looks as though the grey cable is still plugged in. I guess they did something firmware based to disable it.

 

[cwerdna]

I guess they did something firmware based to disable it.

They do it via their Consult III Plus laptop and software.

See NTB17-077 at http://x.nissanhelp.com/forums/Knowledgebase/links/741/.

 

[Lothsahn]

I tried to reverse this idea to see if I could get my carwings back up after the 2G deactivation but it looks as though the grey cable is still plugged in. I guess they did something firmware based to disable it.

Interesting. Doesn't matter, though. 2G cell service is now discontinued. Unless you were making your own cell tower...

 

[Lothsahn]

I guess they did something firmware based to disable it.

They do it via their Consult III Plus laptop and software.

See NTB17-077 at http://x.nissanhelp.com/forums/Knowledgebase/links/741/.

I can't see the exact steps of the TSB. Can you?

 

[cwerdna]

I guess they did something firmware based to disable it.

They do it via their Consult III Plus laptop and software.

See NTB17-077 at http://x.nissanhelp.com/forums/Knowledgebase/links/741/.

I can't see the exact steps of the TSB. Can you?

Yes. Download the PDF w/a free account there.

It's basically, check via the touchscreen that it's the 2G TCU and not the 3G one. Then via C-III plus, diagnosis, telematics, "TCU ACTIVATE SETTING", select OFF then START. Afterwards, check that setting to make sure it's off. At no point do they physically muck w/the TCU, wiring or go behind the glove box.

 

[nateads]

Interesting. Doesn't matter, though. 2G cell service is now discontinued. Unless you were making your own cell tower...

I heard the 2G signal was going to be active until 2020 in Canada.

 

[CML]

Sorry to revive an old thread, but I am finding conflicting info. For a Gen1, and for the purposes of wishing to conserve my 12v battery, should I disable the TCU by yanking the grey connector, the white connector, or both?

The 2012 service manual shows the TCU receiving its power from pins 1, 3, and 4, on the large white connector. So one presumes that leaving it connected, as these directions suggest, it will continue to draw from the 12v battery.
https://carmanuals2.com/nissan/leaf-2012-audio-visual-system-section-av-47811

Also this article does not seem to indicate any issues with removing the TCU entirely, but Euro Leafs may be different? http://www.arachnon.de/wb/pages/en/nissan-leaf/tcu.php

Background: I just rescued a 2011 SL with "12v battery issues". I replaced the 12v with an AGM and all is well so far, but I am paranoid about the TCU. It is 2G and now useless, and I presume it is still wasting my battery looking for long-gone service.

 

[Stanton]

Would be nice if you could give a picture (or direct link) to whatever the "grey or white" connector's are, but if you are asking whether disconnecting power from the TCU will prevent some phantom drain issues, the answer is "yes".
If you want to replace/upgrade to a 3G modem, there are plenty of threads/posts on that as well. Unfortunately, we are looking at a 3G network shutdown within the next year+, so a modem upgrade may not be worth it right now.

 

[CML]

Would be nice if you could give a picture (or direct link) to whatever the "grey or white" connector's are, but if you are asking whether disconnecting power from the TCU will prevent some phantom drain issues, the answer is "yes".

The white connector is the 1-40 pin connector on the left, which is used for power and EV-CANbus. The grey connector is the one in the middle, which connects the TCU to the touchscreen.

Last night I decided to test this. I disconnected the 12v battery, removed the glovebox, then disconnected all connectors from the TCU. There are no dash lights or messages, and the car drives fine, but it does cause a few OBD codes which come back after being cleared.
P31C2 00C0 EV/HEV TCU EVC-273
U1000 00 CO EV/HEV CAN Comm Circuit
P31B8 OOCO EV/HEV CAN Error EVC-287

What's more concerning is what happened this morning! The climate control timer was warming up the car, as expected. I opened LeafSpy, as I have done before while the car is warming up, but this time something under the car started clicking rapidly... wtf?! Quit LeafSpy, clicking stops. Open LeafSpy, clicking starts again. Oh and now I have a new OBD code:
C1A62 0108 BRAKE Control Mod Pwr Supply BR-53

I think I am going to reconnect the TCU for now... The car does not seem to like having an unterminated connector on the CANbus, and I do not want to worry about another bus glitch that could affect my brakes!!!

If you want to replace/upgrade to a 3G modem, there are plenty of threads/posts on that as well. Unfortunately, we are looking at a 3G network shutdown within the next year+, so a modem upgrade may not be worth it right now.

I would upgrade to a 3G TCU if it were worth it, but all signs point to don't bother. I have ordered an Open Vehicle Management System (OVMS v3) instead. The OVMS may require me to disconnect the TCU to enable remote climate control, which is why I wanted to test disconnecting the TCU. I'm hoping that the OVMS will coexist with the TCU, we'll see.

 

[coulomb]

I opened LeafSpy, as I have done before while the car is warming up, but this time something under the car started clicking rapidly... wtf?! Quit LeafSpy, clicking stops. Open LeafSpy, clicking starts again.

I think I am going to reconnect the TCU for now...

Leafspy does that relay clicking all the time. Maybe it's more noticeable with the hood open (i find mine stops when the hood is open).

My guess is that the relay chatter will happen even if you reconnect the TCU. It's most unlikely that the TCU is the end of the CAN bus, with the bus relying on the TCU to terminate it. I suppose you could check for 120 ohms resistance on the CAN bus lines.

 

[CML]

Leafspy does that relay clicking all the time. Maybe it's more noticeable with the hood open (i find mine stops when the hood is open).

My guess is that the relay chatter will happen even if you reconnect the TCU. It's most unlikely that the TCU is the end of the CAN bus, with the bus relying on the TCU to terminate it. I suppose you could check for 120 ohms resistance on the CAN bus lines.

You are correct, the relay clicking with LeafSpy happened again today with the TCU reconnected. On another thread here I discovered this can happen when the car is not powered on. Occasionally LeafSpy does not detect that the car is sleeping and addresses the car as if it were on.

I also discovered that the BRAKE OBD code that appeared was unrelated to this, and likely caused by my disconnecting the 12v battery. I cleared the code and it has not come back.

So my conclusion is that all connectors of the TCU should be disconnected to properly disable it and reduce 12v battery draw. The only negative effect observed are 4 OBD codes, see above. No warning lights/messages or change in touchscreen behavior aside from Carwings cellular functions failing immediately.

Regardless, the codes make me nervous, so I'm going to leave the TCU connected unless I find it interferes with OVMS. Luckily I have the 2G TCU which is not known for staying stuck on. If I had the 3G TCU I'd probably leave it disconnected.

 

[Lothsahn]

Would be nice if you could give a picture (or direct link) to whatever the "grey or white" connector's are, but if you are asking whether disconnecting power from the TCU will prevent some phantom drain issues, the answer is "yes".

The white connector is the 1-40 pin connector on the left, which is used for power and EV-CANbus. The grey connector is the one in the middle, which connects the TCU to the touchscreen.

Last night I decided to test this. I disconnected the 12v battery, removed the glovebox, then disconnected all connectors from the TCU. There are no dash lights or messages, and the car drives fine, but it does cause a few OBD codes which come back after being cleared.

Interesting. I disconnected my TCU (and verified it didn't show on the center console, but never actually checked to see if the wiring matched up. I did notice that when I disconnected the white 40 pin connector I got a number of CANBUS errors, so I reattached it. It's entirely possibly my TCU is still powered on, but just can't talk to the multimedia unit.

I guess a better plan would be to pull the fuse for the TCU.

 

[Dala]

Regardless, the codes make me nervous, so I'm going to leave the TCU connected unless I find it interferes with OVMS. Luckily I have the 2G TCU which is not known for staying stuck on. If I had the 3G TCU I'd probably leave it disconnected.

If we could isolate which messages belong to the TCU, we could have OVMS constantly send them onto the bus and trick the VCM that the TCU is still present, thus avoiding the DTC codes

 

[CML]

If we could isolate which messages belong to the TCU, we could have OVMS constantly send them onto the bus and trick the VCM that the TCU is still present, thus avoiding the DTC codes

I would very much like for OVMS to be a plug-and-play replacement of the TCU. I think this would require putting the OVMS on the white EV-CAN connector, as the codes being thrown are from the EV ECU not seeing what it expects on the EV-CAN. Is this the same bus that is exposed on the OBD port or different?

 

[Stanton]

I guess a better plan would be to pull the fuse for the TCU.

This is the fool-proof way to disconnect the TCU (also used to "reboot" when the old modem used to "hang"), but it also disables some other (audio) accessories if I remember.

 

[Lothsahn]

Regardless, the codes make me nervous, so I'm going to leave the TCU connected unless I find it interferes with OVMS. Luckily I have the 2G TCU which is not known for staying stuck on. If I had the 3G TCU I'd probably leave it disconnected.

If we could isolate which messages belong to the TCU, we could have OVMS constantly send them onto the bus and trick the VCM that the TCU is still present, thus avoiding the DTC codes

Dala,

You would know more than me, but I think there's actually two issues:
1) The TCU isn't present on the CAN bus, so diagnostic codes appear about it missing
2) The TCU may terminate or provide continuity to one of the CAN busses, so if you unplug the connector, you start getting communication errors on that BUS. Perhaps the 120ohm termination resistor is actually inside the TCU?
https://www.ni.com/en-us/innovations/white-papers/09/can-physical-layer-and-termination-guide.html

Would we need some sort of a jumper or resistor to bypass the TCU so that the CAN communication still work?

 

[Dala]

Dala,

You would know more than me, but I think there's actually two issues:
1) The TCU isn't present on the CAN bus, so diagnostic codes appear about it missing

Nope, according to schematics the TCU is on the same EV-CAN as the battery (and the OBD2 port)

2) The TCU may terminate or provide continuity to one of the CAN busses, so if you unplug the connector, you start getting communication errors on that BUS. Perhaps the 120ohm termination resistor is actually inside the TCU?
https://www.ni.com/en-us/innovations/white-papers/09/can-physical-layer-and-termination-guide.html

Would we need some sort of a jumper or resistor to bypass the TCU so that the CAN communication still work?

Nah, if this would be the case then the whole CAN bus would go down. It is perfectly fine to remove modules from the bus, the system still works.

Shame I haven't had the chance to experiment with proper TCU removal at all, haven't had any suitable vehicle to experiment on (and more important stuff going on )