240atcobantech

I bought a 1989 240sx fast back auto trans for my son recently. The car had trans problems when I bought it but the engine ran well and the car would shift from first to second with no problem however I ran the diagnostics that the nissan 240 manual suggested and the over drive light didn't function like the manual suggested. Figuring the trans was shot I pulled the engine and trans together and rebuilt the engine. I bought a trans from one of the ASAP that sells used jap engines and trans. After rebuilding the engine and putting in the use trans, the engine purrs but when I tried to run diagnostics on trans I got same results as before with the used trans. So I followed the diagnostics from beginning and it says if you turn off the overdrive switch and turn the ignition key to start the overdrive light will light for 2 sec and go off and then you run further test. Well the light would not come on while in the over drive position so the diagnostics said to check pin 29 and 30 going into the AT controller and I should have battery voltage. Well I have no voltage at the 29 and 30 pin on the AT controller.

If anyone has experienced electrical problems with AT controller please help me.

I have chased lots of elec problems in my other 2 240sx and have been successful but they are manual trans and this one has me confused.

Good luck to all

Mekanik22

Because you have no power at pins 29 and 30, check for continuity between the ignition switch and the A/T control unit (Main Harness). Also check the ignition switch itself and the fuse.

240atcobantech

I am having problem identifing the color code on wires that are going into pin 29 and 30. It looks like green with a silver dot.

Coming from the stering colum is a white connector with 5 wires (pretty heavy) and none match the wires going into pin 29 and 30. I checked all the fuses in the panel under the driver dash and all check out.

what connector would I find the 2 wires that go to the AT controler. I have studied the elec diagrams and I cant find the information I need.

Thanks again
Bud

Mekanik22

From the ignition switch, look for a green wire with a blue stripe on it. That is your wire. It splits right before the A/T controller to go to terminals 29 and 30. Let me know how you did with that...

Secondly, are you trying to test the A/T controller itself? Because you could just measure the resistance right at the controller itself to find out if it's any good. It's on the right side of car mounted on the right side of the firewall right above the ECU.

240atcobantech

Yes after I discoverd no power to pin 29 and 30 on the controller, I performed test on the AT controller it self and it tested fine. I knew it was a power problem. After dreaming about this for several days a light went off in my head. I work in the IT field and I have a line tracer (hook one end of wire to device it sends signal down wire and you can trace to other end). I did this last night and shazzam it took me to the bottom right fuse holder next to the drivers compartment. The clip the fuse sides in was damaged and pushed back. After repairing this I slid in the fuse hooked the battery back up and everything was working fine. Note to anyone tracing this again the fuse is marked reverse tail lamp, and it also powers the AT controller.

Also note anyone have problems with shifting. I changed this trans because it would not shift from second to third or overdrive. Then I started trouble shooting other possible problems and thats when I discovered the power problem going to the AT controller.

The Nissan Mannual is the best tool for diagnostics and trouble shooting problems. Best tool I have bought yet.

Thanks everyone
Bud