I have searched and searched with very little info to help me understand why my max won’t shift properly. It will shift up but at times it will not downshift and I’ll be stuck in 3rd until I turn car off and restart it. Then I’m good till it acts up again. I have replaced ECM and TCU. When I replaced the ECM, I had CEL again. It was something the old one wasn’t doing anymore. I did reset the ECM and it may have cleared it out because I don’t have CEL anymore. I know one of my O2 sensors needed replacing and I’m wondering if the ECM was good but now doesn’t respond because the CEL isn’t on. I also cleaned my grounds well and battery cables well. Still nothing seems to help with my issue. The harness seems good but I may have to perform test on it. Perhaps someone has had a similar issue and can point me in a direction I haven’t tried.

Also I have looked on net for code and it tells me the circuit between ECM and TCU is open or shorted. In addition, it states it may be faulty TCU. Perhaps I got a bad replacement unit. If you can shed some light on this matter, I’m eager to try something I haven’t. Thanks

 

The P600 code says that the ECM isn't getting the correct info from the TCM. That part you got. But for the TCM to tell the ECM whatever it needs, the TCM has to get some feedback from the transmission. Maybe you should check the wire connections on the transmission. The wire harness connects on the lower front of the transmission, and could have been hit by a rock or something.

 

Thanks Dennis. Let me add more info to help out. My Maxima was having these issues with old transmission and it had excessive play on the differential so I replaced it. I went from A to V so now I have LSD. The transmission came from an I30 with 64K miles. With that said, I think the trouble may lie in the car itself like the wiring. At times the speedo wont work and then it does. I replaced the VSS and still no remedy.

 

Anyone have any suggestions?

 

Probably check all the transmission related wiring and connections for corrosion, continuity, broken wires, and loose connectors.

 

+1 to checking the wiring to the transmission and connector. I am also running a V (most likely from an I30) in a Maxima. No issues.