Chevrolet Repair: 2006 Chevy Trailblazer 4.2L

Question
On the trailblazer when you turn the key to start it, it will crank half a crank and will not turn over at all, I turn the key back and try to crank it again and it is only half a crank again. All the lights and gauges work. The next morning when I tried it started right up, so I move it out of the garage and cut it off and tryied to start it back and it would only do half a crank. Can you tell me what can cause this.

Answer
HI KIM FROM CALIF,WISH I WERE THERE !!!THIS TRUCK HAS A AMP SENSOR ON THE BATTERY CABLE. SO IT KNOWS THAT THERE IS LOW VOLTAGE TO THE STARTER...YOU MAY THINK THE BATTERY IS OK BUT I BET IF YOU JUMP THIS IT WILL START WITH NO PROBLEM AS LONG AS YOU HAVE GOOD CONNECTIONS ON THE JUMPER.. SO IF YOU JUMP IT AND IT STARTS,, GET YOURSELF A NEW BATTERY,,OR BETTER YET TAKE THE BATTERY TO A STORE THAT SELLS BATTERIES AND HAVE THEM CK IT..I THINK THEY WILL TELL YOU THAT YOU HAVE A WEAK BATTERY..ALSO ONCE THIS GETS GOING AGAIN MAY NOT BE A BAD IDEA TO HAVE THE ALTERNATOR CHECKED JUST TO BE SURE THAT IT IS OK AS WELL..THIS WILL CAUSE A WEAK BATTERY IF THE ALT IS NOT CHARGING TO THE CORRECT SPEC. IF YOU HAVE A VOLT METER AND WANT TO SAVE YOURSELF SOME $$$$ HOOK THE VOLT METER UP TO THE BATTERY CABLES START THE CAR UP AND TURN ON YOUR LIGHTS NOW HOLD THE THROTTLE TO ABOUT 1200 RPMS AND THE VOLTAGE SHOULD BE 13.8 TO 14.5 VOLTS ANY THING LESS THEN THAT HAVE THE ALT CHECKED OUT AT A SHOP..BUT YOUR PROBLEM IS MORE THEN LIKELY JUST A WEAK BATTERY....HOPE THIS HELPS YOU AND GOOD LUCK TO YOU,,,TOM..