I have a 1999 4x4, the vehicle is showing code po740 which is the TCC solenoid.
Also the electronic 4x4 is nolonger functional. the button light up when you start
the vehicle and the go out and the buttons do not function. I replaced the TCC solenoid
with no luck on the po740 code. I know the TCM controls the 4x4, can it also cause the
po740 code.

 

Maybe you have a break in the wiring to the solenoid???

If you have a 233 transfer case you would need to check codes by grounding pin 13 (orange wire) on the OBDII connector then watching the lights flash. Crappy selfdiag system with only 4 codes.

236 transfercase you scan with a "real" scanner (little code checker wont work) for trouble codes and data analysis.

I've been replacing a few button assemblieson the 233 ones lately.

TCM (trans control module)??? Your truck aint got one. You have a PCM (powertrain control module) that controls trans and engine, and aTCCM (transfer case control module with 233) or ATC module (automatic transfer case with 236)that controls transfercase.

Forgive me if I seem to be splitting hairs... (I've been hangin around with my wife and she's rubbing off on me)

 

You got any hard shifting, TCC slippin' or other symptoms to go along with that P0740?

How often does it reoccur?

 

As CoolAirVw has stated, you have a TCCM which controls the transfer case and a PCM which controls the powertrain (engine & transmission). Although ATC is a common acronym for automatic temperature control (not to split hairs - lol).

You have two entirely separate problems going on here with nothing in common between them.

This will get you some explanation about the code you are receiving - P0740 Explained

Now, about your transfer case. CoolAirVw is exactly right here as well, but I will write it a bit differently. If you have a regular 3 button switch on the dash (ie. no Auto4wd option), then you have the NVG233 transfer case which can be diagnosed using the information in the following thread - OBD2 Non-Automatic Transfer Case Diagnostics. If you have Auto4wd, then you need a real scan tool as stated and things get more complicated (or easier if you have the scan tool as it gives you more information and more diagnostic capability).

We have seen an increase in push button switch replacements here on the forums lately as well. Seems there are more and more problems being traced back to the switch. If I get a chance later, I may see if I can look up the resistance values for the switch so that someone could check it independantly.

 

Wow those are two really good links.

 

I checked the self diags as suggested by coolairvw and the electronic 4x4 now works.
It has been three weeks and it is still working. I still have the p0740 code, haven't had time to get
into the wiring. Will get back to all as soon as I can.

Thank you, all your help is very much appreciated.

 

What was the returned trouble code and how did you fix it? Or did you just reset the TCCM and hope that it does not happen again?

 

Ran the diags by grounding pin 13 and the 4x4 buttons are now working again.

Also for the Po740 DTC,
Found a broken wire in the harness where it went over the passenger side
valve cover to the ECM (Yellow wire with brown stripe). Was not easy to find!!!!