Dodge Ram Cummins 12 valve tachometer issues Part 1

My 1997 Dodge ram with it's 12 valve Cummins diesel engine has had a strange intermittent problem that's gotten worse. The tachometer is intermittent, random lights on the dash go on and off, and the transmission doesn't shift properly.

[@Reagan.Frakes]

I cannot thank you enough! Best information i have found so far. Cheers!

[@TechGorilla1987]

Dear Steve, you have dove down the rabbit hole on this....we're along for the ride, I guess... XD

[@d9gdon45]

Don't give up on it Steve! I see that every time the tach moves, so does the volt meter.

[@CB-bc3mx]

d9gdon this is what mine is doing ... not charging and no tach ... momentarily works when I start up cold

[@Hutch_moto]

I commenting while I'm watching , but did you adjust trammision TV cable after you put all the throttle cable stuff back in? Dosent have anything to do with electronics but greatly affect shifting. The cable with the D shaped silver button , depress and hold and push nose of that cable assy inward. Then depress acellerator pedal to floor once and you'll hear the cable attach end click several times adjusting its self . Good thing to rule out .

[@chrisbetts4402]

IF the ESS has rubbed ,, its the Rubber in the harmonic balancer allowing the balancing ring to move around a bit , in turn rubbing and ruining the ESS. Id replace AND set the gap to the max recommended . My 94 12 valve just started with its intermittent Tach , so ill look into grounds , wiring trauma , look at and or replace replace ESS sensor ,, also many oddities come from bad solder connections in the dash cluster . Thanks for the VID !!

[@stevewatr]

There were no signs of rubbing on the sensor, and after the replacing the sensor, the issue was resolved, and has not returned to date, that was over a year ago.

[@TWX1138]

If this truck has the 47RH or 47RE transmission, first three gears are hydraulically controlled. This allows the truck to operate the first three gears even without a functioning PCM, since it shifts like the old 727 transmission. Overdrive however is electronically controlled, which requires the PCM to determine the conditions under which the truck should enter overdrive, including throttle position and RPM. I suppose if I were in your shoes I'd see if I could somehow monitor that 5V supply while on a test drive. Unfortunately that probably means tracking down the male and female sides of that connector and building your own inline bit of harness. Now, the advantage of that is that you can test on the other two wires, to see if you're getting some kind of crank position reading. Back in the day there was interest in figuring out how to automatically control overdrive when putting an A500 or A518 into a '70s muscle car. The common solution was a toggle switch that the driver engages to make the transmission upshift to OD, but obviously that's not as elegant as something that could monitor RPM and throttle position and do it without intervention. Not sure if that was ever solved unfortunately, 'cause if it was, then it might at least allow you to have overdrive, even if it doesn't fix the tach problems.

[@stevewatr]

Wow, lots of good information here. I still haven't order the sensor. I plan to rig something with the harness so I can monitor that sensor. Both the 5v supply and the pulse output with my oscilloscope.. stay tuned!

[@AndrewBrowner]

@@stevewatr did you find a solution? got a 96 with the 47RE i believe, drives awesome when trucks first started, but after about 10miles the tach goes wacky and it wants to keep downshifting doesnt wanna use upper gears/OD? i think its staying in 2nd gear not even 3rd, aout 100kph (60mph) is my top speed in that gear when it acts up cant go over 100kph and thats the engine at fuel cut rpm so 80-90kph is a more realistic speed dunno if i should throw a 100$ sensor at it or if its the whole PCM

[@AndrewBrowner]

still watching the videos as im commenting, but im not having any charging issues or engine light/gen light coming on, cruise control doesnt work but i just bought the truck idk if it ever did.. my tach gets shacky and adds 1000rpm under throttle or will just go full rpm right past 4000 .. i just want it to shift properly i dont care about tach or cruise

[@justinmorgan8516]

I’d give anything to have seen this before I spent a small fortune on alternators and batteries. Long story short, my father in law is in the hospital recovering from Covid. He has a 1994 Dodge Ram 2500 CTD with a four speed manual. I’ve been working on it for him, compounding, polishing, ceramic coating. Just want it be right when he finally gets out. The truck would run fine but as soon as you ran the lights, windshield wipers, AC pretty much anything electrical, it would drain the batteries. New alternator, same problem, new batteries, same problem. His tach hasn’t worked for some time and the truck has been sitting for a while ( he has multiple vehicles ) All this makes so much since now. Sometimes some of us have to learn the hard way 🤷‍♂️

[@redrustyhill2]

I am having issues, tach, speedo, alternate, and temp gauge not working. Fuel and oil pressure work. Alternator is charging though. I took a guess and replaced ignition switch because my Silverado had that same issue years ago. That didn't fix it.

[@Luna-dt1nt]

Hi steve i have 97 dodge ram 2500 turbo diesel 5.9 cummins mi problem is that my RPM needle bounces alot and when i reach 40mph my turbo doesn't kick in.....any idea

[@xhongxina286]

I don’t have any problems except the torque converter do you think it could be the tps

[@JyrkiPokela]

Charger fault? Does the Charger excite the relays or functions? The voltage gauge changed when the warning lights came on.

[@stevewatr]

Very good eye. Turns out that when the PCM is not getting a signal from the engine speed sensor, it inhibits the alternator because it thinks the engine isnt running!

[@cheiffmiami7045]

Hi Steve thanks for the video my 1997 dodge 3500 Cummins does the exact same thing but only when I make left turns any advise helps thanks .

[@stevewatr]

In part 3 I reveal that I believe the issue was the crankshaft sensor. I replaced it, and gave not had the issue return. But you left turn only symptom makes me wonder if you have a wiring issue, like a wire grounding out somewhere when the truck makes a turn.

[@cheiffmiami7045]

@@stevewatr I changed the sensor as you did in part 3 and so far so good thanks .looking forward to more if your great videos

[@dalemauritz991]

CCD bus is where the tach signal is transferred through to the instrument cluster from the PCM

[@stevewatr]

It was a bad crankshaft sensor.

[@sandcrewus1362]

Where does the coolant sensor sit at on this truck warmed up.

[@stevewatr]

I don't recall exactly. I can tell you that on a summer day towing a 14000 lb. trailer up a long incline. it will run right up to the high limit line before the danger zone.

[@jimmyjarreau1052]

And when I would turn off the over drive it seems like it jump to gear I didn’t know it had 🙈

[@sorehair7075]

what was the part no. of the sensor and where did you get it?

[@stevewatr]

I bought it on Rock Auto. Don't remember the part number but you can just put in the year and model of truck on their website. Be sure to select diesel engine.

[@jimmyjarreau1052]

Mine does the same but the a/c would cut on and off

[@fredboiton7893]

Did your air conditioning go out as well when you had this issue?

[@stevewatr]

I do not recall. But I know the alternator would stop charging when the pulse was missing.

[@cumminsdaily2235]

Having the same problem on my 1st gen cummins. Its a 93 d250.

[@georgeguthrie2962]

I’ve know many that have had solder problems, but those were 2006 . They had to re tinned.

[@stevewatr]

You mean the PC board connections inside the PCM?

[@gustavoalmanzapena]

I'm having the same issue with my 97 I've had the problem for months I replaced sensors alternator etc but still can't get the truck to charge or run properly

[@stevewatr]

Stay tuned for part 2, I'm going to work on this problem again today. But I have now learned that my alternator is also turning on and off as the tach malfunctions. All of my symptoms can be caused by the pcm not seeing a signal from that ess, aka crankshaft sensor. If you already replaced yours, and still have your issue, I'd suspect a bad ground, or bad wiring. That pulse comes from the sensor up front and has to travel up the fr ok not of the engine, along the drivers side of the engine to the firewall, over to the pcm sitting on the passenger side firewall. Plenty of twists and turns in that wiring harness! Corrosion on the plugs going into the pcm could also cause the issue.

[@gustavoalmanzapena]

It was indeed wiring issues inline fuse solved it thankyou I enjoy your videos great job 👍

[@stevewatr]

Thank you for watching. Don't forget to subscribe.

[@brettleffew1725]

@@stevewatr I'm so lost on my issue serp belt and tensioner broke, first went home pulled out bracket retreaved bolt put together new parts 2 days later truck didn't start got new got jump when 50 miles to work at that point radio shit off dead Batts clock widow's seats all dead last to go was tach jumping got to shop check Batts there bad new Batts checked alt running 12.5 volts co worker boss say alt is bad ,I saw two wires a blue green headed out knew it was something different couldn't remember what it was called go to auto store say alt is bad , sceptical change in parking lot don't wanna kill new batt ,on way home dark lights on no dimming just sitting at 12v even behind alt,only did research checked codes front right antilock breaks intermittent....this week stuck at home pulled most wires in harnesses found one under 1st batt box whole bundle smashed under going to a huge cluster if grounds all look like rainbow melted crayons and two wires under radiator rubbing on rain twisted together? HELP

[@thereptileguyz7265]

There's one other thing you can check there's a little power lead that goes down to two solenoids that are on the driver side the power lead comes down off the battery and it splits and goes down to the two solenoids they have a push on connection that over time ends up loose and they will move around on the top of the solenoids it will cause your dash or your tach to jump around it will kick you out of overdrive and I had a lot of problems until I found it but if you take some pliers and close down the connection just a little and push them back on it fixed everything

[@stevewatr]

Thanks for the tip. In my case it was the crankshaft sensor.

[@samwehlage8859]

Have a little more insight on this? I have a 98 12 valve and when I’m driving and hit a bump it will down shift the transmission and if I watch it just right my tachometer will bounce around for just a split second.

[@rayrogers4729]

Has anyone had this same problem with the truck bring a 5 speed?

[@dalemauritz991]

yes I have a 3500 24v 1998 sport with the nv4500 trans the tach doesn't always follow the engine rpm but ts not the crank sensor I have an edge that the tach function works fine and the pcm in this situation is fine as it's communicating to the DLC to a scanner.

[@johnstrange6799]

It's like a canned good with no label. Might be peaches, but.. it could be chili.

[@rogeroconnor5182]

i would check your main ground for the pcm as well,most sensors are ground triggered thru the pcm. the new sensor will come with what us chrysler guys called pez.... i just threw out a sheet of them last week,they are used on any crank or flywheel triggered sensor. they were made of paper so once the vehicle was started the pez disintegrated.

[@vendetta1306]

I'm an idiot. Turns out my 10 amp fuse for the engine was blown 🤦

[@richardharrison4804]

My 1999 has almost the exact same problem. Tach goes to zero sometimes when I hit a bump. Engine may skip a little. Tach may or may not start working again later. Sometimes, when I switch it off--with the check engine light on, the computer seems to not reboot. Then I remove the battery cables to reboot it to get it to start again! I hate computers because one problem can cause other problems!

[@EdY-rr1cp]

Did you ever find a fix for the problem, I have 99 24valve.

[@richardharrison4804]

@@EdY-rr1cp Yes. Crank position sensor, I think. Replaced it. Tach works off it. No tach, no signal to computer and the engine computer gets "lost", so to speak.

[@EdY-rr1cp]

@@richardharrison4804 Thank you sir, your reply was the exact problem and it's fixed now! She runs and can get me back up in the Sierra's where I have a 20 acre Quartz mine. We are looking for gold, it is there in placer form and inside the quartz. We are located between 2 of the largest producing gold mines in 1849 California history. The Empire Mine and The Rough and Ready mine. It's hard going and the Cummins can take it well. Thanks again

[@richardharrison4804]

@@EdY-rr1cp Glad to help others when I had the same issue. Good luck with your quest!

[@tylerc2627]

The pcm is internationally regulated ( voltage regulator) .... is probably bad...

[@stevewatr]

No. Voltage regulator is fine. Keep watching.

[@KR1IS]

I got a 96 with only 6000 miles