No Crank No start on my 08 Sierra

My 08 Sierra 4.3L recently came down with a No Crank/No Start. A mechanic buddy said it was a bad battery, it wasn’t, then said bad mega fuse, it wasn’t, and then bad fuse box, and again, it wasn’t. I’m not purchasing anymore parts until I’m 100% sure It’s needed! With my test light I tested the starter relay and I’m not getting power to it. Where should I go from here? Anti theft, Park/Neut Switch or ignition Switch? I’m limited to a test light and Multi meter with different probes and clips etc. Any and all help is greatly appreciated!!! Thanks from Central PA and Go Pens!! 

I’m limited to a test light and Multi meter with different probes and clips etc.

No worries, we can work with that.

With my test light I tested the starter relay and I’m not getting power to it.

Let's be clear about no power to the starter relay. I attached a numbered terminal view of the starter relay pins in the underhood fuse box:

 

Key on, starter relay removed. Test light connected to B-, lightly probe all four starter relay terminals. Use a T-pin or thin piece of metal to get down to the terminal if you have to, but don't spread the terminals in the process. Only probe one terminal at a time. Which terminals light up?

Key on, test light to B+, touch all four again. Which terminals light up?

I attached the starter relay diagram for future reference, but it really isn't important at this point. Let us know which terminals light up, and we can go further.

Don’t remember which pins were which but I’ll do the light test to Batt - & + as soon as I get back to my place!! About 10-15 mins. Thank for the help bud!!

When key is on and light was hooked to B- #87 lit up and when hooked to B + #30 and #86 both lit up.

When key is on and light was hooked to B- #87 lit up and when hooked to B + #30 and #86 both lit up

By looking at the wiring diagram above, you should have power on pin 30 and 86. Pin 87 seems to power up fuse 62 that goes to the starter. Pin 85 should be a ground. It doesn't make sense if your test light is hooked to battery + that pins 30 and 86 would light the test light. That is backwards on how it should be.

I’m not sure but that’s what happened when I tested the pins. Just trying to figure out why it won’t crank. Frustrated!!!

Well, if the relay pins are getting the wrong inputs, the truck will not start.

Yeah I know that, but it’s in the correct way so I’m back to brainstorming the cause…maybe if I try whispering sweet nothings to her it’ll fire up?!? Doubt it!! Haha

check your grounds . then with a volt meter, b+ to pin 85 , what do you get ? then your starter solenoid ,does it get 12 volts while someone else cranks engine ?

Do you have battery voltage or does the test light illuminate on pin 86 when the key is in the start/crank position?( Test light or voltmeter lead connected to ground) That will tell us if you are missing inputs.

Tkturns816 wrote:

When key is on and light was hooked to B- #87 lit up and when hooked to B + #30 and #86 both lit up.

I don't mean any offense when I say this, but that's completely opposite of what it should be. 

Is it possible that you were looking at the pins upside down? Because it'd make way more sense that terminal #30 lit up with the test light to B-, and #87 and #85 lit up with the test light to B+. That'd show good power from the battery at #30, continuity through the starter solenoid and fuse through #87 and control ground through #85.

All that leaves is #86. Test light to B-, probe the one pin that didn't do anything the first time around. Have someone else turn the key to Crank. What does the light do?

The relay was upside down thus the numbers being switched… you’re correct 30 lit up on B- 87/85 on B+.
Nothing happened when 86 on B- and cranked.

Test light (lead to ground) does not light on 86 in the start/crank position

Tkturns816 wrote:

Test light (lead to ground) does not light on 86 in the start/crank position

OK then, that explains why the engine isn't cranking. The ECM isn't energizing the starter relay. Or it can't.

If you want to prove out the starter circuit, you can remove the starter relay jump pin 30 and 87. If you choose to jump the pins, make darn sure that:

1.) The key is out of the ignition.
2.) The vehicle is in Park, and
3.) That you are in fact jumping 30 and 87.

If the engine cranks, you can be relatively certain about the battery/starter/cables.

From here, there's only a couple more checks we can do. Does the check engine light come on with the key? Does the PRNDL show Park?

This is the point in the diag where a scan tool is gonna be required. If you don't have access to one, I'm still a big advocate for the TopDon TopScan:

www.amazon.com/gp/aw/d/B0C3QQYQ1B/

The TopScan will get you fault codes, scan data and bidirectional tests so we can narrow down our suspect list.

In the PCM, look for ignition inputs. such as: Start Signal, Crank request, Ignition on/off . Crank the engine and see if they change. If the PCM receives the start signal, the crank request and so on, you are not dealing with inputs and antitheft problems. You will have to check the control wire for opens and shorts before condemning the transistor. Powers and grounds to the PCM may need to be checked as well.( not likely to be the issue, though). 

Ok I will try that after work, greatly appreciate the help!! Funny you mention the TopDon, I was looking at different ones the other night and was looking at reviews etc on it, I believe that’s the one I’m gonna go with!!

Engine does crank when I jump 30/87, it’s is showing the truck is in Park, There is NO check engine light when I have the key in. Which is weird cause I know it was on when it was drivable because of an O2 sensor.?

Not sure what my next move is here but I’m certain I’m gonna be ordering a TopDon OBD2 code reader. Which one should I get? The lite or the pro? Any help and info welcome!! ?

Either will work. I have both and either one will get you the info we're looking for.

If in doubt, go for the Pro. Nothing wrong with having the extra magic button pressing abilities on hand.