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Discussion Starter · #1 ·
2004 Impala LS (3.8L)
Had issues with the speedometer never working, while the tachometer would work sporadically. Replaced all 4 stepper motors within the instrument cluster using Dorman 10-0200F Instrument Cluster Repair Kit. The temp and fuel gages are perfect....they were fine before but changed their steppers anyway. The speedometer has been fixed and now accurately shows when I'm goin' 120+ mph. :)

But the stupid tach no longer works. It only worked randomly before, but after the new stepper it refused to work at all....was giving a negative reading with engine on or off. So I replaced the stepper motor again (tach only) and put another new one in for the tach. The Dorman repair kit gives you 6, so there were 2 extra. Now with this second new one, it reads around 4200 with the engine on or off. At first the needle was moving around on its own independent of engine speed. Now it seems to just be stuck at 4200.

I am thinking the instrument cluster is no longer the problem, and the signal being input is to blame...where does that come from? The coil? Need to track this down....any ideas appreciated. Thx.
 

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I would try to get your hands on a code reader that can show live data. You could then see if the ECU is getting a correct rpm signal. If the RPM is reading correct on the live data, it isn't the CKP and is most likely still an issue with the gauge cluster. When I had a bad CKP sensor, the tach would drop to zero. It would also make the car run quite poorly though too.
 

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Discussion Starter · #4 ·
Good points, thanks. Yeah, the car runs great. If the CKP feeds the ECU and the tach, then the CKP is just fine. If the tach gets its rpm signal from somewhere else, then it might be that somewhere else.

Doubt that 2 new stepper motors could both be bad. It's possible I monkeyed-up the circuit board itself getting the old stepper out and the new ones in. Could replace the entire instrument cluster, but that nullifies the time and dollars spent on fixing this old one. Also, I soldered in some blue LEDs to customize the look, which is rather cool now....except for the wacky tach.

Could just give up on the tach and pull the needle off and put a cool picture there instead....
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