I have a 2008 At G37 coupe.. I was given the wrong transmission from an auto parts dealer. The problem is I already connected the transmission to the engine & it was a hassle. It currently runs on a 2013 seven speed. The computer only reads five gears though…. Can I take an ecu from a 2013 & drop it in? Or should I just swap the tranny?
Also reason I swapped tranny was because I thought it went out. I would drive on freeway and tranny would lock up. Did it a few times so I just switched the thing. Now with this one it did the same. So after it locked up I figured it was an electrical problem. So I disconnected battery waited for a while and transmission hasn’t locked since. What do you think this could be?
Also when I got it all my gauges went out speedometer, rpm meter, gas gauge, battery & a/c module. I checked fuses and sensors I can’t seem to find the problem?
I really appreciate the help I’m struggling with this thing!

 

So the car was originally a 5 speed G37 and you installed a 7AT?

Technically the V36 chassis can take the 7at and possibly run however older BCMs might have the pins going to different locations.
It would have to take some rewiring of the correct pins going to the BCM and CAN system to get it to work, unsure if the board of the 08-09 will display 7 gears if not you'll need to replace the speedometer to a 7at one.

Seems like more work than to swap back to a 5 speed.

 

It runs and works just fine, but like I said only shifts to five gears.
I was thinking maybe if I switch the transmission computer maybe then l.
but yeah it looks like ima have to swap back to an auto 5sp. What should
i tell the dismantlers that gave me the wrong transmission. Technically
I can say I paid for it to get installed and now they tell me this crap.
I was surprised the transmission even connected properly and allowed the
car to run. So far I’ve driven it so San Jose and back twice from Sacramento.
but yeah you have any idea why none of the gauges work by any chance?

 

When you found that the replacement was a 7AT, you should have returned it. 85% of those with the 7AT hate the damn thing... Out of curiosity how much did you pay and where? eBay, local yard, etc.? Paid in cash or credit card? The seller sold you the wrong part. Plain and simple. Call them and see what their policies are for returns/ how they can make it right. If the mixup was a honest mistake they likely will try to make it right for you.

Your specific car was designed for the 5AT- therefore, the BCM, ECU, Unified Meter/& AC Amp (which also controls your gauge cluster), and all the other alphabet soup modules are looking for various CANBUS, AV COM, and other signals from the 5AT TCM ("transmission control module"). The car has no clue that a 6th or 7th gear exists, therefore it stays in 5th. I am surprised it is even working at all. The TCM is located within the transmission itself so swapping it out would not help in this case.

As BULL mentioned above, it is going to take more expense and work to get the 7AT to work with your car than it is worth. Plus, most will agree that the 5AT is a far better transmission than the 7AT.

What did you do with your original 5AT?
Did you try to pull any trouble codes?

 

For the sake of curiosity when doing those that do the cluster swap to older years? Dont you upgrade to the 2010+ board? meaning the cluster should work on the 5 speed? meaning it should be vice versa he could install a 7a cluster and take care of the gear display.
As for shifter it should not matter since it shifts up or down.
The real question is the BCM, wiring should be a bit similar however the BCM is will be the real contender.
@ILM-NC G37S stated something really important and it's the AC amplifier and meter, between the BCM and this meter you'll find the missing link.

For a person that's electronically savvy this could be great news. OP has confirmed that for the most part a 7at will get most of the systems going, for proper operation you'd need to re-wire somethings. I could also be wrong, very wrong

 

From what I gather, any of the clusters are interchangeable, 5AT, 6MT, or 7AT, even Coupe, 'Vert, Sedan,,, the center LCD display reads the data from AV COM (AC Amp) and CANBUS and displays the messages accordingly. Even the newer Q clusters should 99% function (still a work in progress)...

I do not think it is a wiring issue as much as it is a AV COM/ CANBUS logic issue...

Then again, I could, also, be very wrong...

 

Yeah probably has codes havnt checked yet & yeah I got it from a dismantlers in Sacramento called South Sac Auto Parts, paid cash, they were happy to assist me though. They were the ones who informed me of the wrong transmission they gave me. They said if anything goes wrong I can bring it back. 🥲 now I’m on the verge of removing it again. It was a hassle, but I guess it has to be done. I appreciate the help on the transmission.

any reason why none of the gauges work by any chance? All of them are out. Speedometer, rpm, battery, & thermostat.
I bought the car like that, so it was like that before swap.

 

Hard to say. If the problem was like this prior it might be due to power/ground or a system not communicating with the car.
You should check as much as you can prior to taking the trans out. Though the speedometer relies on the trans for speed/ gear/ lights it does not for power. You should at least get the cluster to light up.

 

South Sac Auto Parts seems to be a pretty decent company/ seller. I have bought several parts over the years from their eBay store (saccityautoparts) and never had any issues (except they won't ship large items (damn spoiler )). It might be a hassle, but in the long run putting a 5AT back in will save a lot of headaches down the road. Plus, as mentioned before, the 5AT is more reliable than the 7AT. HOWEVER, I would not drop the tranny again until you resolve the cluster issue, the 7AT may be working just fine for all we know...

Now to the cluster... it would have been nice had you told us it was not working prior to the trans issue...

1. Does the cluster light up at all? Do any of the "idiot" lights come on? With the car off, does the red "security" LED flash? Or is the cluster completely black/ dead?
2. Have you checked any of the fuses? There are two (2) fuses in the left foot fuse block marked: METER (IGN) and METER (BAT).
3. It would not hurt to check all of your other fuses as well. The cluster receives data from several modules (mainly the Unified Meter/ AC Amp) in the AV and CAN buses (intranet) and if they are "down" the cluster will not operate fully.

If fuses are good, then run the self-diagnostic for the cluster itself. This thread has the diagrams to show you how to check that the cluster itself is good. Those results will determine if the cluster needs to be replaced or if the issue lies elsewhere.

Being the cluster is not working.. are you 100% sure the 7AT is not shifting into 6/7th?

Let us know what you find out then we will go from there...