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1689 with HVAC

Posted

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 by ducktape11
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  • Tractorman
    Tractorman

    I think you could temporarialy wire in a LED lamp to the OR/BK wire from Connector #2, terminal #11 of the PCM. Wire the other side of the LED to ground. The lamp would be on all of the time after t

  • IBMobile
    IBMobile

    My truck's 3-4 upshift @ ~45mph with light throttle and stock 4:10 diff.

  • Tractorman
    Tractorman

    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 bod

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  • Author
Just now, Mopar1973Man said:

Did you leave the key on for a long period to wait for the CCD Bus to quit talking?

I turned the truck on and waited 3min.

Should it not be running? Should I wait longer?

On 5/10/2025 at 5:56 PM, ducktape11 said:

Also I remember that turning on my heated mirrors pops the blower motor fuse. I haven't tried using them for over a year because of that and I couldn't figure out the connection between the mirrors and the blower motor.

Since you mentioned this, I did find a correlation between the heated mirror switch and the blower motor circuit. The 10 amp fuse #2 in the junction block feeds Joint Connector #8 which connects to the mirror heater switch and some other components INCLUDING connection to the coil of the blower motor relay. Was it the #2 fuse in the junction block that blew?

  • John

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  • Author
2 hours ago, Tractorman said:

Since you mentioned this, I did find a correlation between the heated mirror switch and the blower motor circuit. The 10 amp fuse #2 in the junction block feeds Joint Connector #8 which connects to the mirror heater switch and some other components INCLUDING connection to the coil of the blower motor relay. Was it the #2 fuse in the junction block that blew?

  • John

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Yes that is correct fuse 2. Yea looking at the diagrams I finally was able to put the 2 together. Very weird they would be on the same fuse. I figured a blower motor on high and heated mirrors would be over 10a draw.

22 minutes ago, ducktape11 said:

I figured a blower motor on high and heated mirrors would be over 10a draw.

It is only the blower motor relay coil (#85 and #86) that draws from this fuse. That current draw is less than 200 milli-amps. The switch portion of the relay (#30 to #87) carries the full load for the blower motor - #12 40 amp fuse in the PDC.

Most likely you have a short circuit to ground downstream of the mirror heater switch / relay that is causing the blown fuse when you activate the mirror heater switch. At least you now know where to begin looking for this problem.

Back to the "no buss" message issue - I will have to think about that some more.

  • John

  • Author
1 hour ago, Tractorman said:

It is only the blower motor relay coil (#85 and #86) that draws from this fuse. That current draw is less than 200 milli-amps. The switch portion of the relay (#30 to #87) carries the full load for the blower motor - #12 40 amp fuse in the PDC.

Most likely you have a short circuit to ground downstream of the mirror heater switch / relay that is causing the blown fuse when you activate the mirror heater switch. At least you now know where to begin looking for this problem.

Back to the "no buss" message issue - I will have to think about that some more.

  • John

Ok thanks!

Yea the no buss is an issue. Disconnecting the fuse, relay, or motor itself at the connector gives the no buss message. To me that means it's power I'm looking for and not ground. Somehow a CCD module is powered off that cable somewhere. But if I disconnect just the motor the circuit prior to the connector should still have power. That's where I don't understand what's going on. If something was tapped into that wire it should work with a disconnection past the tap. The blower motor connector should only be power to and ground from the motor (for high speed only).

I cut the connector for the blower motor out and soldered the wires together due to corrosion in the connector and that changed nothing.

  • Owner
5 hours ago, ducktape11 said:

I cut the connector for the blower motor out and soldered the wires together due to corrosion in the connector and that changed nothing.

Ouch I would of got a pigtail for it and kept the plug.

  • Author
14 minutes ago, Mopar1973Man said:

Ouch I would of got a pigtail for it and kept the plug.

I still have the connectors just didn't have the terminals for inside. I can put it back together eventually

5 hours ago, ducktape11 said:

Disconnecting the fuse, relay, or motor itself at the connector gives the no buss message. To me that means it's power I'm looking for and not ground.

I tend to agree with that conclusion, but I wouldn't rule out a ground issue. Poor grounds can cause irrational behavior and can mess with your mind.

Have you tested the CCD circuit (as described below) while you are making changes in the blower motor circuit? It would be interesting to see if CCD voltage readings reflected a change when the "no buss" message showed.

  • John

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  • Author
2 minutes ago, Tractorman said:

I tend to agree with that conclusion, but I wouldn't rule out a ground issue. Poor grounds can cause irrational behavior and can mess with your mind.

Have you tested the CCD circuit (as described below) while you are making changes in the blower motor circuit? It would be interesting to see if CCD voltage readings reflected a change when the "no buss" message showed.

  • John

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Both voltages were low

2.422 and 2.463 if I remember right

23 minutes ago, ducktape11 said:

Both voltages were low

2.422 and 2.463 if I remember right

Were these readings with the P1689 code set or cleared? Were the readings different with the code set and with the code cleared?

  • John

  • Author
48 minutes ago, Tractorman said:

Were these readings with the P1689 code set or cleared? Were the readings different with the code set and with the code cleared?

  • John

I haven't cleared it since it sets Everytime I leave the blower on too long. Does it change with the code gone?

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