crank sensor?

Discussion in 'General Motoring' started by Suzanne, Jan 10, 2004.

  1. Suzanne

    Suzanne Guest

    It's been 30 degrees below zero lately and my car acted like the
    battery was not even there and there was no sound at all, not even a
    click. I got someone to jump it , then test drove it about 10 minutes
    and the electrical seemed almost normal (heater fan, lights, but not
    the automatic seatbelt). Then I turned off the key and tried to start
    it again and there was once again dead silence, as if I had never
    turned the key. I've searched the internet and it seems it may be the
    crank sensor. Does this sound right? It's a 94 SL2. Could it be
    that I didn't let it charge long enough before stopping the engine?
    Can anyone help me diagnose this? Thanks.
    Suzanne, Jan 10, 2004
  2. Suzanne

    Kirk Kohnen Guest

    It is most certainly something other (SLIGHT maybe in addition to) the crank

    The crank sensor sends pulses to the computer WHEN THE ENGINE IS TURNING to
    tell it where the crankshaft is. If the crank sensor is not operating, the
    starter will turn the engine, but the engine will not start (no fuel or
    ignition because the computer doesn't think it's turning).

    If NOTHING operates (no lights, no radio, no nothing) then suspect the
    battery and the connections to the battery. If things light up, but the
    starter simply refuses to turn, then suspect either the starter, the
    ignition switch, or the park/neutral switch in the transmission.

    If the battery has failed, also check the alternator really carefully (or
    just replace it). Bad batteries kill alternators, and bad alternators kill
    Kirk Kohnen, Jan 10, 2004
  3. The crank sensor would not cause a no-cranking condition. I'd say most
    likely your battery is weak..
    Robert Hancock, Jan 11, 2004
  4. Suzanne

    Bob Shuman Guest

    Sounds like your battery is bad, or possibly the terminal posts/connectors
    are no longer making a connection and need to be cleaned or replaced. I'd
    put my money on the battery. I've seen them fail internally with an "open"
    between the battery cells or the posts. This sounds like what you have here
    to me, although you would need to measure the voltage across the posts with
    a volt meter.

    If this is the case, when you are driving after the jump start, then your
    nominal 13.8V is likely much higher, running at the regulator's battery
    charging voltage, most times upwards of 16V. This can have bad side effects
    on the other electronics (computers, radio, lights, etc.) if not corrected

    Good luck.

    Bob Shuman, Jan 11, 2004
  5. Suzanne

    BANDIT2941 Guest

    The crank sensor would not cause a no-cranking condition. I'd say most
    Definitly sounds like a dead battery to me.....
    BANDIT2941, Jan 12, 2004
  6. Suzanne

    Suzanne Guest

    Are you saying that everytime you have your car jumped you are quite
    possibly damaging components? Also, is it true that it's not good for
    a car to jump other cars? Thanks
    Suzanne, Jan 12, 2004
  7. Suzanne

    Bob Shuman Guest


    When you jump start a car that has a "dead" (actually discharged/less than
    fully charged) battery, the maximum voltage at the jumper cables is limited
    by the two batteries which are effectively in a parallel circuit. As such,
    the theoretical voltage across the jumper cables is 13.8V (6 lead/acid cells
    in series) so assuming it is done correctly, no damage should occur. That
    said, the actual voltage can be a bit more or less depending on the
    condition of the batteries, the amount of current flowing through the
    cables, and the gauge (resistance) of the cables, but this is really
    insignificant for this discussion.

    The damage I was referring to assumed the "dead battery" had an internal
    "open circuit" and this would occur once the car had been started and the
    jumper cables were removed. At this point the good vehicle's battery would
    be removed from the circuit and the alternator and voltage regulator would
    put out maximum voltage without the bad battery being there to hold the
    voltage to the 13.8V nominal. Most sensitive electronics have some form of
    protection built in or are designed to temporarily handle voltage spikes
    from the vehicles electrical system, but I was just stating that if these
    failed there could be permanent damage. Even without a complete protection
    circuit failure, you also risk shortening the life of the components by
    running them at this elevated voltage.

    Bob Shuman, Jan 12, 2004
  8. Suzanne

    Oppie Guest

    Is the alternator on these cars internally regulated or is the regulator
    part of one of the computer functions? The only connection I would speculate
    on is for an externally regulated alternator where the crank signal is used
    to delay application of the alternator field current until the engine is
    started and up to speed.

    I would expect though that if the crank sensor was defective or even
    intermittant, that it would go into limp home mode and throw a service

    educated guesses only,
    Oppie, Jan 12, 2004
  9. Suzanne

    Bob Shuman Guest

    I do not believe the engine could run (even in a limp along mode) without a
    crank sensor since it provides the proper piston timing/positioning signal
    to the engine computer. That said, the computer might be able to infer the
    valve positioning (provided by the cam sensor) from the crankshaft/piston
    position since they are connected by a timing chain, so it may be true that
    it could possibly "limp" along without the cam sensor, but I seriously doubt
    that it could do so without the crank sensor signal.

    This is my opinion based on experience with non-Saturn vehicles. I will
    leave this theory to someone who has a factory service manual and can state
    authoritatively for certain what actually happens if the crank sensor is

    Bob Shuman, Jan 12, 2004
  10. Suzanne

    BANDIT2941 Guest

    It wouldn't run without a crank sensor. There is no real cam sensor per se. The
    computer can deduct which cylinder is firing by monitoring the spark plug
    wires(thats why they need to be crossed) but in order for it to be firing in
    the first place the crank sensor needs to be functional.

    BANDIT2941, Jan 13, 2004
  11. Suzanne

    BANDIT2941 Guest

    I do not believe the engine could run (even in a limp along mode) without a
    Where I wrote something like "which cylinder is firing" replace that with
    "which cylinder is firing under compression" since with the waste spark system
    it fires at every TDC instead of just compression stroke.
    BANDIT2941, Jan 13, 2004
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