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 Friday at 05:25 PM5 days by ducktape11
Added info

Check your PCM power wire for BD noise filter and remove it. Make you have a solid 12V at the power wire of the PCM.

One other member @pepsi71ocean had this problem cause by a poorly installed BD noise filter.

13 minutes ago, Mopar1973Man said:

Check your PCM power wire for BD noise filter and remove it. Make you have a solid 12V at the power wire of the PCM.

One other member @pepsi71ocean had this problem cause by a poorly installed BD noise filter.

Okay I'll look tomorrow. It does have the noise filter on there. I haven't checked the ripple on the new alternator.

17 hours ago, Mopar1973Man said:

Check your PCM power wire for BD noise filter and remove it. Make you have a solid 12V at the power wire of the PCM.

One other member @pepsi71ocean had this problem cause by a poorly installed BD noise filter.

Disconnected noise filter with no change in either issue. I have good battery voltage at the PCM red/white wire. Trans line pressure wire with fooler box goes to max voltage of 4.6v at idle I can go down to 3.2v and up to 4.6v. isn't that too low? I can only get TCC lock up sometimes as far as I can tell. Pushing on accelerator raises RPM much faster than speed so I'm guessing TCC is not locked

Is this thing wire correctly? Shouldn't it be on the green/white wire for governor pressure?

Also the transmission holds 3rd gear a long time but I believe that is due to the 3.54 to 4.10 regear. Won't shift to OD until 45mph unless I'm barely on the pedal.

4 hours ago, ducktape11 said:

Also the transmission holds 3rd gear a long time but I believe that is due to the 3.54 to 4.10 regear. Won't shift to OD until 45mph unless I'm barely on the pedal.

I would suggest you have the ABS computer reflashed with the proper tone wheel size and then rev/mile of your current tires.

5 hours ago, ducktape11 said:

Disconnected noise filter with no change in either issue. I have good battery voltage at the PCM red/white wire. Trans line pressure wire with fooler box goes to max voltage of 4.6v at idle I can go down to 3.2v and up to 4.6v. isn't that too low? I can only get TCC lock up sometimes as far as I can tell. Pushing on accelerator raises RPM much faster than speed so I'm guessing TCC is not locked

Is this thing wire correctly? Shouldn't it be on the green/white wire for governor pressure?

First off measure your AC noise voltage from the alternator after it has been driven and full warmed up. It should measure less than 0.05 Volts AC. Be aware you need a quality DVM that can measure small AC Voltages and multi-frequencies. Being fully warmed up, to ensure the grid heaters are off. Keep the engine running so the restart doesn't trip the grid heater again. I would highly suggest you do the W-T ground wire mod.

You really need to get the TCC to lock up. Without the TCC working, you could create a lot of fluid temperature, so be careful. I really wonder if the noise issues is so bad the filter can get it to shift correctly.

36 minutes ago, Mopar1973Man said:

I would suggest you have the ABS computer reflashed with the proper tone wheel size and then rev/mile of your current tires.

First off measure your AC noise voltage from the alternator after it has been driven and full warmed up. It should measure less than 0.05 Volts AC. Be aware you need a quality DVM that can measure small AC Voltages and multi-frequencies. Being fully warmed up, to ensure the grid heaters are off. Keep the engine running so the restart doesn't trip the grid heater again. I would highly suggest you do the W-T ground wire mod.

You really need to get the TCC to lock up. Without the TCC working, you could create a lot of fluid temperature, so be careful. I really wonder if the noise issues is so bad the filter can get it to shift correctly.

I did the W-T mod already and the alternator and batteries are new. I saw 0.04v ripple DC from the alternator but I did not measure AC. I'll have to look at that tomorrow.

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.

Edited Sunday at 01:37 AM4 days by ducktape11

43 minutes ago, ducktape11 said:

I need to figure out a way to watch the TCC lockup wire and make sure the PCM is grounding it.

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 the engine is started, but it would go out when the torque converter is commanded to lock up. I don't think it would cause you any side effects and it would do what you want.

• John

7 hours ago, ducktape11 said:

Won't shift to OD until 45mph unless I'm barely on the pedal.

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

5 minutes ago, IBMobile said:

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

I figured it was due to the 4.10 gearing. Just sounds long because of the 2000-2100rpm shift

The LED is a smart idea that should work great!!

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

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.

The AC compressor clutch and the Cummins buss both share the common grounding point G107. See 2001 FSM page 8W-90-15 for its location.

30 minutes ago, IBMobile said:

The AC compressor clutch and the Cummins buss both share the common grounding point G107. See 2001 FSM page 8W-90-15 for its location.

Looking at all the grounds and such I didn't see a G107 I'll have to look at my hard copy manual. I did just see G123 that has compressor clutch and CCD - buss? Could that be it?

43 minutes ago, ducktape11 said:

Could that be it?

I think they are the same because in the 2001 FSM there is no G123 shown.

59 minutes ago, IBMobile said:

I think they are the same because in the 2001 FSM there is no G123 shown.

I'll have to find it this afternoon. The weird thing is it does the CCD issues at any blower speed but if you disconnect the blower it only happens at face and floor selections. All other selections are fine. It leads me to believe either a ground is shorted or a wire is somewhere it shouldn't be.

I tried measuring AC voltage with my meter but it's not that great. Even in mV AC setting it would jump between 100-500mV then go to 0 and stay.

Was the truck warmed up completely and left running? I'm trying to make sure the batteries are charged and no big loads are running. That way we can measure a fairly common at rest AC noise levels. Should be pretty steady typically. Jumps are big loads stressing the diodes.

9 minutes ago, Mopar1973Man said:

Was the truck warmed up completely and left running? I'm trying to make sure the batteries are charged and no big loads are running. That way we can measure a fairly common at rest AC noise levels. Should be pretty steady typically. Jumps are big loads stressing the diodes.

Yea I'll double check batteries tomorrow to make sure they are charged completely. But.......

New info.

Had to adjust down the voltage regulator because I got a 3rd gear start for the first time in a long time. That fixed that.

I was driving around and figured out I can get the TCC lockup if I left off the accelerator to a bare minimum for a few seconds then go back to normal. The TC stays locked as I accelerate. I replicated it a few times before going home. If I go from a stop all the way into 4th gear staying on the pedal it doesn't seem to lockup. I never see that "5th gear" RPM drop unless it is locking with the 4th gear upshift. When I know it's in lock up speedo and tach seem to match so that's my confirmation of lockup.

With this info I would think maybe it's a line pressure or APPS issue? I left the batteries disconnected for the night to do a APPS reset first thing in the morning. I also need to see if I have the right fitting to check the line pressures to see if they are too low or too high. Does anyone know the parameters for the PCM to allow TCC lockup? I can't seem to find it anywhere.

I can not seem to ever get TCC lockup in 3rd gear unless I just don't notice it.

Hmmm... Biggest thing I can say is make sure the APPS signal is NOT modified by wiring mods. I've seen people jump the APPS sensor to the PCM to hope to increase the signal and this should not be done.

1 minute ago, Mopar1973Man said:

Hmmm... Biggest thing I can say is make sure the APPS signal is NOT modified by wiring mods. I've seen people jump the APPS sensor to the PCM to hope to increase the signal and this should not be done.

I'll double check the wiring. When watching it on scan tool it seems to be reading fine.