A good customer called and said that on the way to work the security light came on in the dash and when he got to work the engine would no longer crank up. I suggested the normal check the battery cables, try cranking it in neutral instead of park, tilt the steering column up and down while cranking and doing a possible security system relearn. Nothing worked so he arranged to tow it to the shop. Luckily when it arrived the problem was still there so I started checking. Everything seemed fine except for the obvious no crank condition. I decided to check codes and found an security system code and faults for two oxygen sensor heater elements. I thought that the O2 codes were a little strange but I continued on. I cleared all of the codes and rechecked. Still did not crank and the security data looked okay. All of the instrument cluster lights worked properly and cycled as designed in the crank position.
These trucks like many vehicle have a crank fuse and that was the next step. I already had the ignition on but not in the crank position and when I touched my test light to the fuse test point the starter engaged and the engine started up. THAT IS NOT SUPPOSED TO HAPPEN!!! What is supposed to happen is the test light should illuminate when the ignition is cycled to the crank position.
I checked the wiring diagram for the starter relay, located in the under hood fuse box and found that there either had to be a badly damaged wiring harness or a faulty ground. The customer maintains this vehicle too well to have a harness damaged but he did say that he had recently replaced the intake gaskets because of a coolant leak. I of course knew, that there is a ground wire that attaches to the stud at the thermostat housing so I checked it. Sure enough I touched the wire and it was loose.
I slid on a piece of heat shrink tubing and crimped a new terminal on the wire.
Placed the heat shrink tubing over the terminal base and heated it with a heat gun.
This is the original terminal.
I attached the ground wire to the stud and cranked the engine. One big problem. The engine still would not crank. What did I miss? I went to the diagrams and component locators and found that the ground that I was looking for was on the right side of the engine block. A little searching and I found that the ground I was looking for was actually much lower down on the passenger side of the engine. It attaches to a stud behind the lower radiator hose. It was loose but in good shape. I tightened it down and the truck was fixed. I also found that this terminal provides a ground for the oxygen sensor heater elements. The two codes that I thought were a little strange. The customer had been very meticulous in replacing the intake gaskets including fully removing the wiring harness from the top of the engine which of course required the ground be removed. Just forgot to tighten it all the way down.