crank sensor?

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

Reply to
Suzanne
Loading thread data ...

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

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 batteries.

Reply to
Kirk Kohnen

The crank sensor would not cause a no-cranking condition. I'd say most likely your battery is weak..

Reply to
Robert Hancock

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 quickly.

Good luck.

Bob

Reply to
Bob Shuman

Definitly sounds like a dead battery to me.....

Reply to
BANDIT2941

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

Reply to
Suzanne

Suzanne,

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

posts/connectors

Reply to
Bob Shuman

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 light.

educated guesses only, Oppie

Reply to
Oppie

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 defective.

Bob

Reply to
Bob Shuman

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.

Jamie

Reply to
BANDIT2941

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.

Reply to
BANDIT2941

MotorsForum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.