Check engine light on and doesnt shift when driving?
 

My 1999 Infiniti i30 wont shift when I drive it stays it one gear and kills my gas like no other. How do I fix this I replaced the knock sensor last night and still doesnt

The knock sensor wouldn't be the problem, it is something that tells you that you have a problem, so replacing it won't fix anything.

Is the check engine light on? I would think it should be. Regardless, get the codes read and see what that might tell you.

Check the level of the transmission fluid. If it is low, it can prevent the transmission from shifting.

Let us know what code you have when you get them read.

Also, run the automatic transmission self diagnostic test and see what that might indicate.

The directions start about half way down on page 49 in this link - http://boredmder.com/FSMs/Infiniti/I30/1999/AT.pdf

Here's the codes
 

https://cimg6.ibsrv.net/gimg/maxima....aa60b3814f.jpg

https://www.autocodes.com/p1605_nissan.html

P1605 Nissan Maxima
Possible causes Weak battery Faulty Transmission Control Module (TCM) Harness is open or shorted between TCM and Engine Control Module (ECM) Poor circuit electrical connection between TCM and ECMP1605 Nissan Description The malfunction information related to Automatic Transmission is transferred through the line circuit from Transmission control module (TCM) to Engine Control Module

P1600 Nissan Maxima

Possible causes

• Open in back up power source circuit
• Faulty Engine Control Module (ECM)
• Engine Control Module (ECM) harness is open or shorted
• Engine Control Module (ECM) circuit poor electrical connection

check fuses and connectors to the ECU/TCM first, then check wiring. after that, see if anyone can chime in if failing TCM is common on these. as said, check your trans fluid level before anything since low fluid will cause horrid problems

I will lean towards the Transmission Control Module (TCM) being the problem. If you want to get a new one, the part number is 31036-4L701 and the price is several hundred dollars.

Visit a junkyard and get one from there. The 99 Infiniti and Maxima use the same TCM. Only get one from a 1999, the other year cars use a different TCM.