Hi All,

Been lurking for a while and have found this site very useful, so I thought it was time I write down what I have found and hopefully get corrected if I have any of this wrong. Back story: I purchased a 03 G35 coupe 5AT with 178k miles and a blown motor. The guy I bought it from had no idea what was wrong, his mechanic had told him he needed a replacement. In taking the engine out there was some heat damage to the wiring harness.

So far I have removed the engine and transmission together and would like to replace both with something lower mileage. Around me, 03 RWD engines are priced higher than 06 - 07 engines by around $500 and have higher miles, so I would rather go with the newer motor. So here is what I think I know about drivetrain compatibility.

1) I need a RWD engine since FWD and AWD VQ35DE blocks have the motor mounts located differently than RWD. There are conversion motor mounts available, but price at $500 on the low end.

2) Salvage yards say that the 03 RWD sedan engines are not compatible with the 03 Coupe. From what I have read, people have done this swap successfully and are also confused why the sedan engine is not cataloged as a viable replacement motor.

3) 2004 coupe engines are not cataloged as compatible with the 03 coupes. I believe that this is due to a change in the ECU between 2003 and 2004. In turn, I believe that if I take the wiring harness and ECU from the donor car everything should work, even if the donor car is a 2004 - 2007 (*Keys are chipped so I will need the dealer to reflash the donor ECU to match my current keys).

4) 6MT transmissions are supposed to be plug and play with the 2003 coupe all the way through 2007. I do not know if this is the same for the AT transmission. I have read that the TCU was moved inside of the transmission in later years for the G35, but this could be false since my source was someone posting in a comment section. Maybe someone can confirm with the year of transition?

5) The bell housing on all transmissions 2003 - 2007 (at minimum) are the same, meaning that an 03 transmission will mate to a 2007 engine. This would be good to confirm in case the thing about the TCU in #4 is true.

With all of the above in mind, the current plan is to buy a 2005 - 2007 RWD VQ35DE with original wiring harness and ECU and a 2003 5AT transmission.

One unknown is if the later year wiring harness will be able to plug into the 03 transmission? Ideally, someone out there will be able to confirm that any year transmission will work in the 03 coupe (even though the TCU is mounted away from the transmission under the glove box) so I can take the matching transmission from the donor car.

While I still have my own questions about this build, I would be happy to help out anyone else with their questions as I have learned a lot in getting to this point in the swap.

 

If you're going to swap in a 6mt into your 03 with an automatic. You may want to consider the difference in the rev up motor going into a car that didn't come with a rev up motor.

 

How bout 06 coupe auto .wat other trans is compatible