Weirdness...I took a longshot and unhooked the battery for like 5 min...the needle rolled back around to the top side of the 0 peg when I turned the key on...and worked normal when I started driving...got to where I needed to go turned truck off, and when I stated again it is doing like first described...registers about 3K or higher, other than that it sits on 0 or like 200...UGH Oh well, all I need is the redline anyway...LOL. I rarely pay attention to the tach except when towing...and it just so happens that a friend is moving on Monday...so it figures it'd F___ up on me...$30,000 68,000 miles 4 years...Oh well, guess I had a good run...let the service begin...

 

Ok, I am at a loss as to what to think. Last night I was really hot rodding the truck...this morning when I left for work, the tach was working perfectly normal. Starting to think the tach just likes to drink beer...like me

 

Reset your cluster gauges...mine was acting up such as holding 300 RPM at 70 MPH, or idling at 0 RPM... Hold down the odometer pin, the one to go from total milage to trip and resets the trip data, then turn your keys to ON...all the lights will light up and the gauges will go to different settings I think about 5 different positions. Mine is working fine after that.

 

Start by downloading the 06 Srvc Man from the link in my signature and start at page 1869

OPERATION

The tachometer gives an indication to the vehicle operator of the engine speed. This gauge is controlled by the instrument cluster circuit board based upon cluster programming and electronic messages received by the cluster from the Powertrain Control Module (PCM) on vehicles with a gasoline engine, or from the Engine Control Module (ECM) on vehicles equipped with a diesel engine over the Controller Area Network (CAN) data bus.

The tachometer is an air core magnetic unit that receives battery current on the instrument cluster electronic circuit board through the fused ignition switch output (run-start) circuit whenever the ignition switch is in the On or Start positions. The cluster is programmed to move the gauge needle back to the low end of the scale after the ignition switch is turned to the Off position. The instrument cluster circuitry controls the gauge needle position and provides the following features:

² Engine Speed Message - Each time the cluster receives an engine speed message from the PCM or ECM it will calculate the correct engine speed reading and position the gauge needle at that relative engine speed position on the gauge scale. The cluster will receive a new engine speed message and reposition the gauge pointer accordingly about every 88 milliseconds. The gauge needle will continually be repositioned at the relative
engine speed position on the gauge scale until the engine stops running, or until the ignition switch is turned to the Off position, whichever occurs first.

² Communication Error - If the cluster fails to receive an engine speed message, it will hold the gauge needle at the last indication for about three seconds, or until the ignition switch is turned to the Off position, whichever occurs first. After three seconds, the gauge needle will return to the left end of the gauge scale.

² Actuator Test - Each time the cluster is put through the actuator test, the tachometer needle will be swept to several calibration points on the gauge scale in a prescribed sequence in order to confirm the functionality of the gauge and the cluster control circuitry. On vehicles with a gasoline engine, the PCM continually monitors the crankshaft position sensor to determine the engine speed. On vehicles with a diesel engine, the ECM continually monitors the engine speed sensor to determine the engine speed. The PCM or ECM then sends the proper engine speed messages to the instrument cluster. For further diagnosis of the tachometer or the instrument cluster circuitry that controls the gauge,