1998 4.0 Classic 2WD -

This persistent little code keeps the CEL light on, and the TC will not lock up. I'm clocking 2200 and change at 70 mph and should be right at 1900-1950, if I can use my '96 Sport performance as a guide.

About 8 months ago I dropped the trans pan and replaced the screen, gasket and all the solenoid valves. I did this because the kit was cheap and it didn't make sense not to considering it was in response to fighting code 0704 at the time. I assumed (and still assume) that the TC solenoid is good. I reset the computer and the code remained off for about a week. But, the TC wasn't locking up. This truck doesn't see much highway travel so I haven't been sweating the cure. Now it bugs me so I'm chasing down the problem. I replaced the brake light switch when I changed the brake vacuum booster about 6 months ago. The CEL light remained on. I separated the harness connectors at the trans dip stick, cleaned the contacts and reassembled them. The CEL light persists.

I was under the truck today and watched the shifter movement as my son shifted the transmission through the gears. There's a shaft that exits the transmission on the left forward side. The shaft has two opposing wrenching flats. There's a hex nut that appears to be retaining the shaft bushing with a lock washer that has bendable tabs. As the shifter was moving the shaft with flats was also moving, and so was the nut and lock washer. That doesn't seem right. I would think the nut secures a bushing that the shaft rotates inside of but I'm not familiar with the thing. Is it operating correctly? Also, the nut is not snug and has some free rotation. The lock washer tabs are preventing it from spinning off entirely. Could this loose nut be related to the TC lockup problem?

What other electrical/mechanical items should I troubleshoot to clear this CEL light?

Thanks.

 

Did you mean P0740 for t/c circuit malfunction, as P0704 seems to be for a clutch position switch? Also, it sounds like you're looking at the NSS on the passenger side?



I would inspect the wiring from the trans computer to the transmission. There are two connectors on the passenger firewall where you can disconnect and check the solenoid resistance. One goes to the NSS switch on the passenger side, and the other is the wiring harness to the trans on the drivers side. The t/c wire will be dark-blue/white (pin 11 on the trans computer itself), measured to ground should be 11-16 ohms. I would also check the brake switch and probably backprobe pin 23 on the trans computer and make sure you see the voltage change when you press the brake pedal (FSM says it's a white/pink wire).

-Chris

 

Yes. Dyslexia runs in the family. Code 0740 is what's tripping the CEL light. Your pic is exactly what I'm looking at. That nut rotates with the shaft. Is that normal? I did find the wire on the transmission controller pin-out diagram and it agrees with yours. I'll have to put a meter across it tomorrow. This narrows the search, thanks.

 

Yes it's normal for that shaft and nut to turn when shifting. That's the NSS switch that tells the trans computer what position the shifter is in and controls the reverse lights.