2nd gen PCM functions

[Laidback]

Can someone tell me what the functions of the PCM are for a 2001 Ram 2500 4x4 automatic? I recently had the transmission rebuilt and the ECM replaced but the transmission seems to be slipping at 75-85 mph. I was told by the guy that replaced the ECM and programmed it that it’s a PCM issue but when I called trying to find someone to replace or repair my PCM they are telling me it is an ECM issue. All of my gauges seem to be working fine but my heated seat buttons on the dash light up when I crank the truck and they will flash for a while and then the hi light on the drivers side stays on all the time. The heated seats haven’t worked in a couple of years. The only issue that I know of right now is the transmission feeling like it’s slipping when you just barely give it any throttle it’s not wanting to stay in a high gear. 

[Me78569]

PCM handles all trans functions.   The ECM is purely limited to engine control.

 

 

Trans slipping at that high of a speed suggests a overdrive issue.   I doubt your issue is a computer issue.

[Laidback]

It actually feels like it’s slipping at all different speeds but I know it shouldn’t be slipping after lock up occurs that’s why I specified 75-85 but it does it at 35 and 40 also  

The transmission was just rebuilt buy a highly respected mechanic that rebuilds these transmissions all the time and has a couple of these trucks himself and he’s telling me everything is mechanically right. 

[Tractorman]

If it is only doing this in third or fourth (overdrive), it could be that the converter is unlocking and relocking - about 100 -200 rpm difference.  That could feel like slipping.  If this is the case, the cause could be electrical noise.

 

- John

[Laidback]

How do you solve electrical noise?

[Me78569]

 

ensure you troubleshoot before you attempt to solve. 

 

Did it slip at 75 mph before your trans rebuild?

 

 

[Tractorman]

Electrical noise can come from several sources - poor battery condition, poor electrical connections, poor grounds, a bad diode in the alternator, etc.  There is also a wiring modification article (called the WT Wiring Mod) that corrects all lot of electrical problems.  As I am writing this, I see that @Me78569 has posted that information.

 

- John

[Laidback]

Thanks! 
I pulled the 140amp alt fuse and drove about 30 miles home, slip unlock-lock gone! I reinstalled the fuse and drove 10 miles and it hasn’t unlocked on me yet witch seems strange. I’ll see on the way to work tomorrow. I just replaced the alternator about 10k ago but I guess the diodes have burnt up again. Are the Nations alternators really worth the money? Only has a one year warranty. 
 

Prior to this alternator the old ones kept surging from 12 to 14 V the entire time you were driving, but that hasn’t happened since I got this one. I was told that was a diode issue also so I guess that’s why I didn’t think it was the alternator again since I wasn’t having that issue yet. 
Thanks for the help!

Edited August 13, 2020 by Laidback

[Mopar1973Man]

On 8/12/2020 at 8:06 AM, Laidback said:

Can someone tell me what the functions of the PCM are for a 2001 Ram 2500 4x4 automatic?

 

PCM is a the master computer. It controls the entire CCD network. 

• Cruise control
• Transmission control
• Charging system
• Automatic trans shift controls
• Fuel gauge
• Volt gauge
• CCD Network 

Then next in line is the ECM... Which controls all the Engine functions.

• Tach signal
• Oil pressure
• Coolant temp
• Fueling VP44 (main function)

 

Then the instrument cluster is the bus bias... Required module to set the bus voltage bias of 2.49 and 2.51 Volts.

 

Central timer handles security, cab functions like heat seats, stereo controls, etc. 

 

CCD network allows all information to be shared over just two twisted wires. Remember the PCM is the primary computer the ECM is the secondary computer.

Edited August 16, 2020 by Mopar1973Man

[Laidback]

Thanks guys, replacing the rectifier/diode fixed my torque converter lock/unlock problem. Three weeks later it’s back. What will cause the rectifier/diode to keep burning out? I called the shop that replaced the rectifier and he says there’s a problem somewhere causing it to burn up the diode. 
Also I looked at the link with the article about wt wiring mod but don’t see the wiring mod only alternator testing and a note talking about the wiring mod. All help is appreciated. 

[Threadzy]

Try this one. 

 

[IBMobile]

You can replace the diodes at home.  the diodes are sold in the store here.   

 

 

There may be another problem causing the diodes to go bad such as one of the batteries going bad or a bad cable/connection between batteries or ?.  You need to have the charging system fully tested and do the W-T ground wire mod along with this modification shown below.