OK so I have an electronics mystery for all the gurus here-

Recently I noticed my tach would start to jump around-both at idle, and off idle-but only by a couple hundred RPMS. For instance, at idle, it will sit at 700 RPM, then drop to 500 RPM, then to around 450 RPM, and then bounce back up to 700 RPM. When I do a fast idle to cool the turbo down, I'll set it at 1100 RPM-but then after about 20 seconds it'll fall to 900 RPM (actual engine speed unchanged-so it's just the tach), and then it'll bounce back up again.

Thinking that my crank sensor might be going bad, I replaced it the day before yesterday with a new Mopar unit. Easy install, but I still have the same problem-ALTHOUGH, I have to admit, it's not happening as frequently as before. I just went through the service manual, and activated a dashboard gauge reset-and before I did that, I disconnected the battery grounds for 20 minutes.

When I activated the dashboard reset, I got code C447, S127, 285 in the odometer window, but the "Check Engine Light" hasn't popped on, and the motor runs just fine.

I can't find these codes in the FSM at all, so I don't know where to start tracking down the issue.

Any ideas? If it continues to do this after the dashboard reset, I'm thinking the computer might be fried.

Any takers?

 

Oh, and by the way, when I activated the dash gauge reset, the tach went through all its calibration points-which, the FSM manual says, means the gauge itself is working OK.

 

I would think that if the engine speed sensor was acting up the engine would not run right. I think the dash uses info over the J1939 not straight from the sensor itself. Gotta love chrysler, my father has to slap the top of the dash in his Jeep to get his tach to stop bouncing around. Could be a loose connection under the dash? Hope that helps.

 

Hahaha! So whenever it starts acting up, I should just slap it? I'm not even going to go there

 

OH C'MON GUYS 66 views and no one else has any ideas? Has anyone seen this before their alternator gives up the ghost?

I did notice tonight pulling out of work that my dash lights were dimmer than usual, but over the drive home, they brightened up to normal. The intake grid heater fired before start, and then twice after start-

Could low battery voltage cause the issue with the tach? Are the voltmeters on our trucks just dummy gauges? I thought they were real-

 

This is a pretty typical thing and a lot on the 06's. Its either the cluster or the cluster controller that is generally the problem. ECU is possible but not as likely.

None of the inputs go directly to the cluster controller they all come out of the ECU and the controller just sets the gauges based on what the ECU says it should.

The last person I talked to had the cluster controller and cluster replaced and that fixed it. Others have not said what they did to fix or if they did.

 

Thank you no6-appreciate your help. The FSM does say that if a gauge doesn't sweep when you activate a calibration sequence, that the entire cluster is bad and needs to be replaced.

I'll have to look and see where the cluster controller is to see if it's something I need to take to the *******, or do myself.

 

Never said that was the permanent solution. He just doesnt have the knowledge or money to put in a 10 year old vehicle. The moral of the story is that chrysler uses cheap electronics and wiring. I had a '99 jeep similar to his and the radio went out, the wiring that goes through the door gap fell apart, and one headlight was always dimmer than the other. About the only thing I trust on my truck is under the hood and has a different badge.

 

mine would have a hiccup when it idled, the plug blew out of the cp-3going down the road and they replaced it and it hasnt done it at all since been about 45k since they did it in june so it mite be your cp-3 acting up. yera and nobody really replied or gave me an answer when i posted the problem