Diagnostic Testing vs. Trial (Guess) and Error

[dave]

Here is a fun little success story that happened yesterday…

my autozone buddy who does a lot of side work had a 1999 Chrysler Sebring towed to his shop yesterday… ‘no start/no crank’ condition.

i got out of school and rolled into his shop at about 10pm to help him with his situation. From what I had gathered, he had been to the junkyard twice and had put in his second starter. he then went on to explain that he thought through the process of elimination that the only viable cause of the no start had to be the computer and/or ignition module. at this point he had been working on the vehicle for 5 hours.

within 15 minutes i was able to demonstrate that the starter that he had just put on the vehicle was crap. although the starter did engage via jumping the B and M terminals, jumping the S terminal did not result in a start. I tested voltage at the S terminal and there was all kinds of varying wild readings. I then looked at the wire going to the S terminal and it was frayed and torn in at least 3 distinct places. furthermore, it appeared that someone at some point had already attempted to repair this wire but had done a craptastic job. I then jumped the S terminal directly from the battery and there was no reaction at all from the starter.

at this point, i grabbed the starter that was originally on the vehicle and put it in a vice and bench tested the starter.. fired right up. i was able to debunk all the wild rumors and crazy speculation by demonstrating that the starter solenoid on the newly installed component was bad, the original starter was good, and that the root cause of the problem was an intermittent open in the starter circuit.

my diagnositic premis was simple: for a no start/no crank condition, i first check all the obvious stuff (battery voltage, connections, ingition lock cylinder, neutral safety switch, and ask for any pertinant history or event that may have contributed to the current condition of the vehicle) I then go right for the starter itself and see if it is getting what it needs; constant source voltage at B terminal, switched battery power at the S terminal, and a good ground (measuring voltage drop or forcing the starter to operate can demonstrate good ground) Once I noticed there was erratic S terminal voltage, I was able to specifically narrow down the problem.

although my friend is an expert at wrenching, he is probably not the best at electrical diagnosis. and i have to say it was damn fun walking in and setting everyone straight on what was actually going on in just minutes. after 6 hours of work, swapping the starter and doing a pro wire repair, the car fired right up.

The main purpose of sharing this real life story is to demonstrate how good testing and diagnosis will triumph over trial and error guessing. in this case it could have saved him 1/2 a day of work. banana:

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[mckrishes]

+1

Time and money saved, both of which are valuable.

[Author]

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