Tach problem
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Joined: Nov 2008
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From: CT
Tach problem
Well this past weekend was the first time I really had my truck out this year and noticed my tach is roughly 400 rpms off at idle and progressively gets worse the higher the rpm... Has anyone run into this and know what could most likely be causing this? Thanks for any help!
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Joined: Mar 2009
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From: South GA
Page 1869 of the 06 Srvc Man
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, (Refer to 8 - ELECTRICAL/INSTRUMENT CLUSTER - DIAGNOSIS AND TESTING).
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, (Refer to 8 - ELECTRICAL/INSTRUMENT CLUSTER - DIAGNOSIS AND TESTING).
Moderate User
Joined: Oct 2008
Posts: 17,003
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From: Albany, NY
Just what Owensue said. press the trip button while you turn the key to the On position(don't start) and then release the trip button. The guages will begin to sweep one-by-one. If your tach sweeps smoothly and completely, then it's not the cluster.
Registered User
Joined: Jan 2007
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I did the test and mine sweeps completely and smoothly. What to do now? My tach seems to "leak" down when at idle or under constant throttle. Any advice?
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Registered User
Joined: Oct 2010
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I have this problem with my tach...it is intermittent but is happening more and more. Tach will work and then while driving it will just drop to zero. Once I go to accelerate either from a stop or while in motion, tach will go from zero to about 8K when I am only slightly on the gas pedal. I have done this test and gauge moves smoothly, just wonder if it might be the cluster itself or something maybe "less" expensive 
Professional
Joined: Mar 2009
Posts: 151
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From: Manitoba, Canada
It's an 06 thing...I think you need to replace the stepper motor, but I don't know for sure.
I tried to re-flow some solder in my cluster as someone had a write-up on here, it seemed to help, but only lasted a very short period of time.
I tried to re-flow some solder in my cluster as someone had a write-up on here, it seemed to help, but only lasted a very short period of time.
Registered User
Joined: Jun 2014
Posts: 2
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I can repair this issue, it is in the cluster please email me for more information teg.travisbarnes@gmail.com