Credit: Sparky’s Answers
This 2004 Nissan Maxima came in with the complaint that the transmission would not shift properly. The customer stated it felt like the transmission was starting in a high gear. I really did not want to work on this vehicle as the customer informed me that the engine and transmission had both been replaced with used parts. You just never know what you will run into when going behind someone else. First the code checks.
Code P0335 stored in the PCM. although the customer had not complained about it, I had noticed that there was an extended crank time before the engine started.
The TCM had a code P0726 stored for a CAN Failure system. In case you were wondering CAN stands for Controller Area Network. This means that there is a communication problem between modules.
With the key on and the gear selector in the manual shift position the gear indicator in the instrument cluster shows that the transmission is in the 5th gear.
I wanted to do a little research, in that I have never seen a code P0726 before and I wanted to know a little bit more about it. I found that there are some real world anomalies with the factory diagnostic procedures. The TCM is supposed to use a crank sensor signal along with other data to determine shift patterns. The real world has found that cam sensor signals are also involved with this process. The engineers it seems did not plan on this or they did not inform the service information writers about it. Since I did have a crank sensor code I decided to start there. The crank sensor is located at the bottom center of the engine just below the flywheel area.
Everything looks okay here or does it? Kind of strange how the end of the connector looks like it is lined up perfectly with the edge of the sheet metal shield. A gentle pull revealed that it was not fully seated.
Could it be that it was that simple. This vehicle had been to two other shops before arriving at mine. Using a pry bar, I straightened out the sheet metal shield.
Then installed the connector until the lock snapped into place.
Of course while I was looking around at the problem I noticed quite a few things out of position.
Gee, you think a wiring harness laying on an exhaust pipe might cause some problems?
It amazes and worries me that someone can actually get an engine and or transmission in and out of a vehicle and leave something like this a mess. I had to round up a few bolts and finish installing a couple for brackets and heat shields. Then reroute the oxygen sensor wiring so that it would not be laying on the exhaust.
It does not look too bad now but I informed the customer that the engine installation needs to be gone over to make sure nothing else is loose or not installed.
Now the shift indicator shows that the transmission is in 1st gear. Both the PCM and TCM codes are now gone. The engine also starts as it should.
This one will be back in a few weeks to finish going over the wiring under the hood.