Thread: Tach drops to zero

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  1. #1 Tach drops to zero 
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    My 3.8L SC, 2001 Grand Prix has started to develop a problem. The tachometer sporadically drops to "0" and the TCS comes "on." On occasion, the "check engine" light comes on also. When this happens, there is a slight sputter but the comes continues to run. Upon shutting the engine off and restarting it, the tach and TCS returns to normal. Will this eventually stop my engine and what is wrong with it?
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  2. #2 Re: Tach drops to zero 
    Turbo is the way to go. BillBoost37's Avatar
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    Have you pulled the code?

    It sounds like a crank sensor. However having the code would help out. The TCS is odd, usually you don't get that with the crank sensor.
    I drink..so consider that when reading my posts.

    2010 Audi A6 Dual IC's
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  3. #3 Re: Tach drops to zero 
    GTX Level Member tod1d's Avatar
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    Most auto parts stores will scan your car for free to tell you what code happening.

    2007 Pontiac Grand Prix
    http://www.cardomain.com/ride/2990036
    L26, CAI, HV3, ER Rockers, PLOG, Overkill Tune, flipped dog bones
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  4. #4 Re: Tach drops to zero 
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    Mine had the same symptoms, its the Crank position sensor.
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  5. #5 Re: Tach drops to zero 
    GTP Level Member Oxfire's Avatar
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    Mine had the same thing happen. Didn't really look into rectifying the issue but the gist that I'm getting is that it's the CPS, as people have mentioned. Good luck!
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  6. #6 Re: Tach drops to zero 
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    My '99 is doing the same... I will check into the cps and let everyone know how it goes.


    Thanks.
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  7. #7 Re: Tach drops to zero 
    GrandPrix Junkie PurpleGuy's Avatar
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    Cranks sensor
    2001 Regal GS, PLOG, 3" DP, 1.9's/L76 springs. 21* of timing on a 3.4"
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  8. #8 Re: Tach drops to zero 
    Donating Users RareGMFan's Avatar
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    If there is an interruption in the signal from the crank position sensor to the tach due to the CPS going bad, the tach will drop to 0 and not move again till you reset it by shutting the car off and turning it back on. It will also often trigger the "TCS Off" light if 1 of the 2 needed signals coming from the CPS is interrupted, so given your symptoms, it's almost a guarantee that it's the CPS.
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  9. #9 Re: Tach drops to zero 
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    My 2000 GT 3.8 had the same problem. It would then stall for no reason while driving on the highway, in the city, stopped at a light. Taking the advice from here I replaced the crank sensor haven't had a problem since.
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  10. #10 Re: Tach drops to zero 
    GXP Level Member coolone's Avatar
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    If... And a big IF the crank sensor doesn't fix the problem, the wiring harness near the PCM that passes the evap/condenser gets uncomfortably close and over time can rot out wires from HEAT in that portion of the harness (experience).

    If all else fails, you can check there (but only as a last resort).

    Overkill BBC Cam, YT 1.8 RR's, Rhodes Lifters, STGII Heads, GenV, Pacesetters, 3" Exh to Tips, TEP Trans. N*, ID 75# injectors/E85 coming soon
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