Neutral safety switch test on 02 Trailblazer

[Starship]

Having a no crank condition on my 02 Trailblazer, I can jump the starter to crank but when using the key all I here is clicking sound coming from the PCM , how can I test to see if the neutral safety switch is my problem ?

 

[The_Roadie]

Welcome!

The PCM doesn't have any components to click, so I strongly suspect the noise is the starter relay inside the front fuse block. Trivial to test - pull the relay and see if the clicking goes away. If the relay is clicking and the starter fails to spin, you have a problem in the wiring from the relay to the starter, or a problem with front 40A Fuse #34.

When did the vehicle start last, and was any work done on it recently? Any other behavior changes?

 

[Starship]

Thanks roadie , checked the 40 amp fuse # 34 with a voltmeter for resistance and it checked out ok , removed the starter relay from the undergood fuse box and turned the key to the start position and still got a switching sound from the PCM module mounted on the right side of the engine, I then removed the single purple wire going to the starter , hooked up a jumper cables to it and the battery ground to my voltmeter resting on the hood so I could see the meter from inside the truck , turned the key to the start position and presto ... 12.6 volts going to the purple wire , I then knew it was a dirty, bad connection on the wire , cleaned it good and reinstalled it , and it now starts great .... Fixed
Thanks again Roadie for the help

 

[The_Roadie]

Thanks for the report. Glad to help, even if I was wrong about the clicking. I worked on designing a test system in 1991 for Ford PCMs made by Motorola, and I thought all components inside were solid state and no relays. And I assumed GM used the same general design principles as Ford. But I admit I never did the test of pulling the starter relay and listening, so mea culpa.

 

[PennTB02]

.... hooked up a jumper cables to it and the battery ground to my voltmeter resting on the hood so I could see the meter from inside the truck , turned the key to the start position and presto ... 12.6 volts going to the purple wire , I then knew it was a dirty, bad connection on the wire , cleaned it good and reinstalled it , and it now starts great .... Fixed

It does my heart good to know the old, tried, and proven ways still work (at least some of the time) and the first step in succesful trouble shooting is not always "Go to Auto Zone and have them read the codes." Makes me think I can hang on another year or two before selling all my wrenches and moving to the rocking chair.