I have an 01 Excursion 7.3 4x4 and pulled the codes P0743 & P1744 after the truck felt like it lost 4th gear. I have pulled the plug off the trans and tested for continuity to see if the wiring was shorted to ground. I found 3 wires were grounding out however these three according to the wiring diagram for this truck were not for the TCC solenoid (2 wires were for power feed from PCM and 1 was for the sensor signal return). While I was under the truck I tested a few other wires as 4x4 has not worked since I bought the truck and I have replaced just about every part trying to get it to work, both of the leads going to the transfer case electric motor were also grounding out. Additionally on the plug for the DTR sensor I have 3 wires grounding: start signal from column, reverse lamp and signal return.
I followed the wire loom and disconnected it at the connectors under the hood right by the PCM plug and tested the wires again, no more grounding out on any wires.
My next course of action will be to disconnect PCM and test again if they are still grounding, is there anywhere else I should check?
Is it possible that the solenoid itself is throwing this code given that the wire is not showing it is grounded?
Could the PCM be the culprit in all of these scenarios or am I likely looking at a few different culprits (wiring/pcm and trans solenoid)?

 

Check the TCC circuit for continuity from the PCM connector to the trans connector. Do this with the PCM and the trans connector unplugged. Probe the back of the connector, never put the probe into the end that makes the connection. That can open the pins and make a new problem.

 

At the moment, I'd be most concerned about possible improper testing procedures or misinterpreting meter readings that may have taken you down a lengthy rabbit trail instead of focusing on the PCM-indicated faults.

1. When making resistance readings, ensure that there is no power in the circuits (disconnect battery or remove applicable fuses).
2. When making continuity checks, make sure you use a low range.
3. When checking for shorts to ground or power lines, start with a high range (ie, 20KOhms) then use a lower range if the higher reading "fails". Make sure you disconnect the PCM first.
4. Be careful checking circuits that have incandescent bulbs on them as those bulbs will characteristically have low resistance readings. Same for circuits that power relays as the coils will only present a few dozen or hundred ohms resistance to the meter.

As for the DTCs, focus on the P0743 as a failure in that circuit can also trigger the P1744. Follow Mark's advice.

For the first two, see items #3 & #4 above. The signal return line is supposed to be grounded to chassis ground. IIRC, that connection is made inside the PCM.

 

Thank you for the replies

Removed PCM today and tested continuity from PCM connector to trans connector on TCC circuit, showing 0.3 ohms

Batteries have been removed for entirety of testing.
My multimeter auto selects range and is audible, I have cycled through all ranges today manually to verify the the multimeter is not throwing off readings.
PCM has been disconnected for all tests today.
I do not believe any of the circuits I am testing have bulbs in them.

I pulled PCM, I am now not showing any wires grounding out with the exception of the ESOF connectors, both of these wires are grounding (problem for another day).

I am not finding any fault in the TCC wire, it has not shown to be grounding and it has continuity. Is the solenoid a possibility? This trans was rebuilt by a shop almost 2 years ago and I do not see a charge for a solenoid on my invoice.

 

Can the solenoid set off the P0743 code?

 

Yes, it can

 

I pulled and replaced the entire wire over the weekend just to be safe. I did find one tiny pinhole in the wire so hopefully that was the issue, if the problem persists I will go after the solenoid. Thanks

 

Test drove and it threw the code again after clearing. Anywhere else I should check or would the solenoid be the best bet?

 

It can be the wiring, the solenoid, or the PCM. I listed them in the order of most likely to least likely, but all three are possible.

 

Update - no more code
Replaced the Solenoid last week and drove daily with no return of code. Thank you for your help