GGAutobiz: 2005 Impala No-crank Condition Check

I have a 2005 Impala LS in the shop for a no-start problem. Diagnostics is the procedure to find the cause of the problem and in this case the first step was to turn the key to start. There was no starter engagement, no starter solenoid "click". It's called no-crank because the engine is not turning, the starter is not working and not cranking the engine.
I saw that the dome light was working, dash lights working, headlights working with key on. I turned the headlight switch on and turned the key to start again, The headlights stayed bright and on. It seemed safe to assume it wasn't a battery voltage problem.
It would be a good time to check that the starter was or wasn't getting crank voltage at the solenoid but checking at the starter wasn't the easiest way to check. I would have to get access to the solenoid from underneath the car.

This car has an easier access point in the under hood power block. I always like to say that in diagnostics you are looking for a test point that will give the most information for the least effort. A crank relay in this case, and the easy access makes this a diagnostic sweet spot.

Remove the cover and remove the relay and the connectors can be accessed easily with a circuit tester.

A wiring diagram of the system can look complicated but it really isn't and lets you know what you are testing for electrically. I have seen people start in checking circuits with no clue what they should be looking for. I don't understand the point of that. Anyway.... the only part to be concerned with at this point is what should be at each of those four relay connector points. Power at B8 with key ON or START, power at C8 at all times, ground at C10 in START, power out to starter solenoid on B10 when closed.

Checking for power at C8 and B8 was easy. Just touch the circuit tester probe to the connector pin. Checking for ground at C10 while the key is in START position was easier using a relay tester that allows for easy test lead connections even with the relay installed.

With the probe lead connected here on C10 I could see the relay was being grounded on START. Connecting to B10 with no relay installed and seeing the green display means the circuit to the solenoid from this connector pin was not open, so no wiring problem between the solenoid and the relay.

With the testing so far we know that everything going TO the crank relay is as it should be to make the starter engage. We know the wire FROM the relay to the starter solenoid is connected. We need to test with the relay in place that we have power FROM the relay when the key is in START position. Yes there is power FROM the relay. I'm confident enough now to go ahead and order a new starter but there are still a couple things to check.