So I've come to the almighty moparman forums seeking help on an unusual issue I'm having. My truck is heavily modified by the previous owner and I'm constantly having to fix one thing or another and chase things.

So I have 2 issues now 1 of which I believe I know the issue but don't know a good fix.

First issue is I get trans limp mode and a P1689 with no buss on the CCD when turning on the HVAC blower at any speed. Once turned off it goes back to normal. I have taken the ground off for the HVAC controls and the no buss issue also happens without the blower motor running only in face vents or floor vents position.

Looking at wiring diagrams I can't tell where any of the HVAC would cross with CCD modules.

Second issue I'm having is TCC lockup. I have increased line pressures and a DTT box to decrease the voltage to 4.5v all the time. It engages sometimes but not others and the only way I can tell is just by RPM at 60mph. It's 1 tick below 2000rpm with 4.10 ratio rear. I believe maybe the DTT box is bad or the line pressures are too high? What is the TCC lock up algorithm? Sometimes if I left off the pedal and slowly accelerate it will be locked. It's easier to tell if it's locked when I'm towing which is what I use the truck for.

Thank you for any help! I'll provide any info y'all need and hopefully I can get this all figured out!

Edit* forgot to mention I have done the following things to try to fix both issues.

PCM grounded to pass side battery negative

W-T mod

New batteries and alternator

Disconnected a/c relay and compressor( didn't fix so I guess it's not in the a/c circuit)

Edited April 18Apr 18 by ducktape11
Added info

I need to get home and really look over the wiring maps to see if I can see a reach between these two (CCD Bus and blower motor)

55 minutes ago, Mopar1973Man said:

I need to get home and really look over the wiring maps to see if I can see a reach between these two (CCD Bus and blower motor)

Yea every wiring diagram I've looked through I don't see how the HVAC blower or vent position would mess with the PCM.

Also I drove quite a bit today and I can pick the TC Everytime by letting off the pedal, getting lock, then reapplying pedal. It stays locked and even if I let off all the way or hit the brake disengaging the TC it lock right back up without issue until I downshift to 3rd or lower. That tells me the PCM is not sending the signal for lock because of some parameter in missing...

Edited April 25Apr 25 by ducktape11

On 4/25/2025 at 3:12 PM, Mopar1973Man said:

I need to get home and really look over the wiring maps to see if I can see a reach between these two (CCD Bus and blower motor)

Were you able to find anything? I'm not too much in a rush I only drive the truck when I tow my camper. I'm stumped at this point because as long as I don't use any HVAC stuff all is well besides the TCC lockup.

On 4/18/2025 at 9:52 AM, ducktape11 said:

My truck is heavily modified by the previous owner and I'm constantly having to fix one thing or another and chase things.

Maybe the previous owner has messed up the wiring somehow. It may be worth physically tracing the CCD bus circuit to see if any wiring has been damaged or tapped into.

• John

Just now, Tractorman said:

Maybe the previous owner has messed up the wiring somehow. It may be worth physically tracing the CCD bus circuit to see if any wiring has been damaged or tapped into.

• John

I'll have to take a look and trace the wires from HVAC. Do you know if everything on that circuit is supposed to send 12v to components?

Most of the the HVAC circuit consists of switches in the ground side and there is a blower motor relay and an AC clutch relay as well as a refrigerant low pressure switch. There is a 12 volt supply to the blower motor and the AC clutch relay.

I would be more inclined to trace wires in the CCD bus circuit as those pair of wires can only be connected to components operated within CCD system - nothing else.

Not that Joint Connector #7 is a hub for connecting to many of the CCD components in the system.

• John

On 4/19/2025 at 9:35 PM, ducktape11 said:

Would AC noise cause no pickup? I don't have the typical symptom of lock/unlock. I need to figure out a way to watch the TCC lockup wire and make sure the PCM is grounding it. My scanner won't give me any transmission live data no matter what I do. Barely any ECU stuff.

Also for the WT mod I put the grounds directly to the battery negative and not the block then the battery so I will do that as well.

The noise can do all sorts of things to your lockup

Should lock up at 48 in normal driving conditions and you should tell a noticeable drop in rpm and driving, not just when towing.

On 4/21/2025 at 12:39 PM, Tractorman said:

I suspect that you may have a poor body to frame ground, or poor body to battery ground. Since the blower motor switch grounding and the data link grounding are in the body ground circuit, a poor body to frame or body / frame to battery ground connection could influence the CCD circuit. Body ground # 200 (located on the driver side inside the cabin) and engine ground # 107 are part of the CCD circuit.

You could temporarily run a jumper cable from the body directly to the battery ground post and then operate the HVAC blower fan to see if the symptoms go away.

• John

I agree