12v 2nd Gen Cummins tachometer failure [update]

This is a follow up to the 2nd gen 12v cummins tach, cruise, a/c, O/D failure.
Thanks for watching.

[@altadutch]

I share your frustration with this. The other day my tachometer, speedometer and overdrive stopped working so now I’m wondering what’s happening. At first I thought it would be a blown fuse but now I’m not so sure. Have to go back and check. My 95 truck only has 115km on it cause I don’t need it much. Always starts easily though.

[@anonknowledge]

Another thing to try is while having someone sitting in the cab, wiggle the wiring harness at the PCM. If any erratic jumping or flatline of the tach occurs you may have to monkey with how tight the bolt connecting the two is. I found mine works with the harness bolt looser (the pins may have a bad connection).

[@altadutch]

@@anonknowledge thanks for replying! I’ve left multiple comments about my trucks issue on various sites and don’t remember where......... I used to do most of my own repairs but at 76 am not that flexible anymore and eyesight difficulties, lol.

[@bishboi3629]

Little late, but I have a 95 12 valve, bought it from the first owner, Speedo didn’t pass 15mph, no cruise, fuel gauge reads empty, no o/d unless I give it 0% throttle, but still has lockup, ended up being that piece of the cluster, Speedo fixed, still no o/d. I noticed my tach flutters barely at idle, didn’t stumble my mind until I noticed it flutter more for a couple seconds then stop, I checked the plug for the engine speed sensor, found a zip tie holding it still, took it off, spread the prongs to help with the connection, still flutters and no o/d or cruise. I have been cleaning all my grounds and my pcm is good nice solid connections and I did the wiggle test, tv cable is set properly and isn’t stuck. I haven’t checked the engine fuse in depth, nor the brake petal trick, which I will do now. I will make a KZbin video in the near future detailing everything. Hopefully it’s the fuse, brake petal switch, or the engine speed sensor!

[@altadutch]

I just wanted to update my post. My problem was fixed by having the crankshaft position sensor replaced.

[@bishboi3629]

@@altadutch I just changed mine, same thing no o/d and a slight bounce in the tach at idle and no cruise. Checked my fuses and the brake switch. I believe I have a pcm ground issue I am going to ground it and hope for the best! My ac and Od switch work and I have put a 1k resistor in the trans temp sensor wire as well. Thanks for your reply

[@jarendahl4632]

Having this problem with my 94. Tack works intermittently wither associated problems ( no ac od or charge) I have used an occiliscope and see the 5 volt pulse go in and not out of the pcm. There’s huge resistance about the engine bay when it’s not working. Do you know where the pcm ground is?