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Original post by: Nope ,


This can be caused by a few things.  To diagnose it you need to work backwards:

1. Bad battery or low charge, or bad connections at the battery terminals.  If the terminals are full of white snowy looking stuff disconnect them and clean them up.  If a terminal is loose (you can turn it with your hand) tighten it.  Check the battery voltage.  A fully charged car battery would read about 12.6 VDC.  12.3V is 50% charged.  Less than that and you will quite often have a starting problem.  Even if the battery voltage seems OK you should try jumping  the truck to see if it'll start - a failing battery may have a reasonable voltage readout but very little capacity available, making it unable to start the vehicle.

2. No power to the starter motor or a defective starter motor.  What's called the "starter" has 2 power connections - a large wire that provides power to the starter motor, and a smaller wire that powers the starter solenoid.  When  the key is turned to start the solenoid will engage the gear on the starter with the ring gear on the flywheel as well as trigger the starter motor to begin turning.   If there's no power to the starter motor but power everywhere else you'd hear a "click!" noise when you turned to start but nothing else - ie. no whirring or cranking noises. If you don't hear that click (you might need someone to stand outside with the hood up to hear it) go to #2.  The cause of this problem is usually one of 3 things - a failed starter motor, a bad connection between the battery and starter motor, or a blown fuse (if present) in line between the starter and the battery.  A test for DC voltage between a ground point (eg. battery negative terminal or the engine block) and the large wire  on the starter can diagnose a blown fuse (it will read 0V) but it can't be used to indicate if the connection or starter are ok.  The simplest way to diagnose that problem is to clean the battery terminals and the large starter terminal ('''MAKE SURE TO DISCONNECT THE BATTERY + TERMINAL BEFORE DISCONNECTING THE STARTER CABLE OR YOU COULD GET A SEVERE BURN''').  If it still isn't starting take the starter off and have it tested (you can test it yourself if you can mount the starter somehow so it won't jump, connect jumper cables to the battery with the - cable going to the metal body/frame of the starter and the + connected to the big starter terminal AND the small solenoid terminal at the same time -  but be forewarned that if the starter isn't firmly mounted it'll jump like crazy and can hurt you!).

3. If the starter isn't clicking you have a problem in the starting circuit that drives the solenoid.  Start by disconnecting the solenoid wire (the small one) from the starter.  Use a voltmeter to test for DC voltage between that wire and a ground connection (battery - terminal or the engine block) when the ignition is turned to Start.  Make sure you're getting good, solid connections to ground and the wire or you'll get a false result.     If you don't get around +12V there's a problem earlier in the circuit.  Go to step #3.  If you do get +12V clean the terminal on the starter and the cable and reconnect them and try again.  If it still doesn't start you've got a bad starter solenoid.

4.  Unfortunately this step requires a wiring diagram.  In it's most basic form the way the starting circuit  works is this:

Battery==>Ignition Switch START switch==>Starter Solenoid

However, all  vehicles add other things in the circuit, with modern vehicles sometimes being very complicated.  A (simplified) example would be:

Battery==>Anti-Theft==>Autostart==>Ignition Switch==> Engine Control Unit ==> Starter  Solenoid

With fuses and other items in there as well, and with a number of parallel connections being made (eg. the ECU would also trigger the fuel pump, fuel shut off, etc.  before triggering the starter).

The way it would be diagnosed is to follow the wiring diagram from the battery up through the ignition switch and out to the starter solenoid.  There should be 12V at each point along the way (after the ignition switch the 12V would be present when the switch was turned to START).  When you find the first point with no voltage the previous component is the problem area.  However, if the problem is at the ECU or the Anti-Theft or Autostart the actual problem may be in a completely different circuit altogether - eg. it's not uncommon for some aftermarket autostart system to prevent a car from starting if the hood switch is damaged or not working correctly.