Driving to work yesterday, on the highway at 65 or so, everything is normal.Noticed that the tach needle burped... went from 2000 rpm to halfway to zero to a second then back up to normal.Another mile down the road and it got worse... tach needle went to zero and the overhead display shows "CCD" or the like. Engine runs fine, not a miss. Tach starts working a bit later and the overhead display returned to normal.Got to work and shut the truck down and restarted it and it runs fine, checked for codes and did not find any.Anyone ever have this happening and if so what in the world is it?? Thanks,FT

The cam positioning sensor comes to mind, it runs the tach. I believe it would be unusual for a code not to be set though.

Dave,Thanks and that would make sense on the tach not working... but what in the world would connect the tach and the overhead display? Hmmm.... and just drove the truck home and it ran fine, tach worked normally and display as well with no codes.Lets see... and would a cam sensor cause the engine to die or any other issues? Thx,Joe

The CCD network runs thru alot of the truck. I am defenitely the wrong person to offer advice on that. I have never lost a cam sensor in my truck, the wifes Dakota yes. It was intermittent and the truck would run rough, then run fine for while. I have read similar descriptions from others here when theirs went.

Here is more information on the CCD Network. http://articles.mopar1973man.com/general-cummins/34-engine-system/81-ccd-data-bus You should get 2.49 and 2.51 volts at the OBDII when the bus is functional.

Definitely sounds like the cam positioning sensor. Any other symptoms, such as low voltage, cruise control not working, maybe check engine light?

Interesting... did not receive ANY notice from the board of the last three replies... Thats why I had not replied until now.Drove the truck today and ran fine one way... then coming back home the tach died again and so did the overhead display, but only in the mileage portions, not the temp and so on.Then finally had the truck throw a code. A P1696 code, which I believe means "P1696 PCM Failure EEPROM Write Denied"... I tried to erase the code while driving but it kept giving me an error message. Then tried it again after getting home and "no code found!" Truck seems to be running fine but did "hiccup" once while on the road, something that its never done before.Suggestions? Ideas? EDIT, is this an item or part that can cause the truck to die out on the road or just something that needs to be fixed when I get the time/money? I can live without the tach for a bit but if its going to cause me to die on the road somewhere then thats a different story.Thx,Joe

Still sounds like cam postion sensors, they are about 60$. When mine went out at first it was bad when cold. Bit it got bad enough that truck acted like a miss. Change cps and have had no trouble since.

If I remember corectly, on the 24V as well as the 12V, the alternator runs through the ECM, as the voltage regulator is built into the ECM...I know on my truck the voltage regulator started going bad, which started to cause my tach to jump around. I got around this by wiring in a Ford external voltage regulator-I believe MoparMan did this too, and has a write up on it. Not sure if same between the 12 and 24v's, if that could have the same effect, but if the Cam sensor doesn't fix it, I'd look there...

If I remember corectly, on the 24V as well as the 12V, the alternator runs through the ECM, as the voltage regulator is built into the ECM...I know on my truck the voltage regulator started going bad, which started to cause my tach to jump around. I got around this by wiring in a Ford external voltage regulator-I believe MoparMan did this too, and has a write up on it. Not sure if same between the 12 and 24v's, if that could have the same effect, but if the Cam sensor doesn't fix it, I'd look there...

Denn, Mine does not move around but either works fine or the tach needle drops to zero and stays there and at the same time the overhead display on any of the "fuel modes" gives the CCD error display. Klcammie, Thanks and how much trouble is it to change out? I have just done a VP-44 but not that familiar with the Cummins engine. Thx, Joe

My understanding is the voltage regulator is in the PCM and not the ECM.

speed sensor in the transmission need cleaning ?

My understanding is the voltage regulator is in the PCM and not the ECM.

Correct the Voltage regulator is indeed in the PCM.

The cps is easy 1 10mm bolt. Getting to it is the hard part. If you have skinny hands you might reach it. When I did mine I unbolted the vacuum/power steering pump assembly to make it easier,just move them a little don't remove them. I think it was 30-45 min job.

The cps is easy 1 10mm bolt. Getting to it is the hard part. If you have skinny hands you might reach it. When I did mine I unbolted the vacuum/power steering pump assembly to make it easier,just move them a little don't remove them. I think it was 30-45 min job.

Thanks for the process on removing or loosening the vacuum pump. A question for the group... I had not worried about this that much as the truck is running fine. Just had an issue pop up. An old friend of mine, a 84 year old gent needs something moved about 350 miles from here. I am the only friend in the group with a truck. Is this CPS something that can stop the truck out on the road or do I need to make sure that its changed out before doing this trip? He needs it moved next Tuesday... and of course its raining the next two days here! Lastly, any suggestions where to buy one of these? The dealer or aftermarket place? Thx, Joe

Mine never shut down in the 4-5 months that it was going bad. I don't know if it would. I just finally got tired of the tach. not working right.

I stand corrected...both Dripley and Moparman are correct...not sure why I typed ECM, but the Voltage regulator is in the PCM. My fault, thanks for the catch! Also, when my tach started having issues, it would just randomly drop-and then a few minutes later start working again, so it wasn't always just bouncing around on me.

Ok, have the new Cam Sensor in my hot little hand and of course ran out of time to change it out before my 700 mile drive tomorrow. Am taking it with me but anyone who has done this before, could they please give me an idea of what tools to take "just in case" it dies out on the road? Thx, Joe

If anyone is curious, drove 745 miles in 14 hours flat, with 30 minutes for lunch, 50 minutes to unload an antique airplane off of the trailer one fuel and two "load check" stops, all with no issues and not even a hiccup from the Cam Sensor. It did throw a code twice which was reset at fuel or rest stops, otherwise drove just fine!