Ted K

Greetings, 1st post here. I started my career as a mechanic back in 1966 with a 2 year vocational school program. I twisted wrenches for 7 years before becoming service manager at an implement dealer. Way back when, I knew every nut and bolt on a Chevrolet. Fast forward to today, I am trying to help a widowed neighbor lady. I'm a tad out of my comfort zone now! Her 2005 Suburban will not crank. She had purchased a battery for it and I installed it. No start. I determined there was no power to the starter solenoid when the ignition switch was fully engaged to the start position. I jumped the solenoid at the starter and the engine cranked. This told me that the battery, battery connections, and starter were in operating condition. I checked all of the fuses that were indicated as having to do with ignition and all were good. I switched the starter relay located at the under hood fuse box with another identically marked relay. That didn't help. I watched a YouTube video that showed how to jump the # 37 terminal of the starter relay. With the ignition switch on, the engine started and ran fine. So next I replaced the ignition switch. Still would not crank. The next shot in the dark was to replace the neutral start safety switch. Still would not crank with the key. When the ignition switched is turned to the start position all the dash lights go out and I hear a very faint momentary noise. There is apparently a faulty connection somewhere in the circuit or some component that I have no knowledge of. Without a starting circuit wiring diagram I am at a standstill of where to look next. So I would appreciate any suggestions and/or where to find a wiring diagram. Thanks in advance for your help!

Pierregirard

In my experience, if the dashboard lights go out when you try to start the car, it might be because of a bad ground connection. I'd suggest checking the ground connections for the engine and chassis. Look out for any corroded or loose ground straps or cables, especially the ones connected to the engine block and chassis.

Ted K

Thanks for the response. I too thought that the dash lights going dim is normal but wasn't certain. I initially suspected bad cable connections somewhere but if that was the case I doubt it would work when "hot wiring" the relay terminal. Thanks again!

mountainmanjoe

nice work troubleshooting so far.

electrical schematics (and indeed the whole service manual) can be found here:
https://charm.li/

In this situation, an OEM level diagnostic tool is going to be very useful. I would use it to verify that the ECM is receiving the signal to crank and responding correctly.
I would also use a meter or test light to probe terminal 86 in the starter relay socket, to see if the start signal is reaching it.

This truck is almost 20 years old, so this will most likely end up being a wiring fault (broken/corroded wire or connector). It could a bit of tedious probing and testing to pinpoint it though.

Ted K

Thank you for this pertinent information. I only have a short amount of time today to work on the vehicle. I will look at the wiring schematic and check for power at terminal 86 this morning. I'm unfamiliar with the OEM diagnostic tool. Is this the tool that several parts supply stores will hook to your vehicle? Also can you recommend a good one to purchase? Back in my day, a Sun oscilloscope was our engine diagnostic tool (along with Volt, Ohm and Amp meters) so I'm unfamiliar with the OEM tools of recent times. Would you be so kind as to tell me the proper way to use this tool to verify that the ECM is receiving the crank signal? Also, if it is receiving the crank signal can I assume the ECM is faulty? I'm guessing at that point it may be faulty, but that it would not rule out several other things such as a broken wire or bad connection beyond the ECM. Thanks again for your help! TK.

Ted K

I checked for power at terminal 86 this morning. There are 3, #86 terminal locations on the inside the cab fuse block. I don't have power at any of these. I tested in the ignition switch on only position and in the start position. Where does the #86 terminal receive it's power from? Thanks, TK.

mountainmanjoe

OEM = Original Equipment Manufacturer. As in, the one that GM techs use. They have fancier ones now, but back in '05 it would have been the Tech2.
I don't think part stores use these. They have their own suppliers. I would expect those to only be capable of reading trouble codes.


It would have to be one capable of supporting bidirectional control and OEM special functions. They are aimed at professionals and costs approach the $1,000 mark
You can read an overview here: https://carkiller.com/scottykilmer/h...-should-i-get/
You probably don't want to invest that kind of money if you aren't a mechanic.

Those are still useful tools. But these days everything is computer controller, so you need something that can interface with the computer in the vehicle to check out the various systems, read sensor values, etc . They are a huge help in finding causes for problems.

It's not really something that can be covered in a forum topic. You'll need to find a skilled operator.


No.


Correct. Wiring problems are FAR more common than faulty ECMs. Especially on a 20yo vehicle
That's where the multimeter comes in.

the starter relay one.

there should only be power when the key is in the start/crank position

It should say in the electrical schematic. From the ECM I think.

Ted K

Thanks again for your time and help! TK

a55bruce

The starter relay (under the hood fuse block) should have power on 2 of it's terminals. Sorry this schematic does not show the relay terminal numbers.
There are 3 fuses that are in the starter circuit. IGN E (10A), IGN A (40A), CRANK (10A).
The starter relay coil (85 or 86) gets power from the IGN E fuse via the Park/Natural Safety switch.
One of these terminals should have power all the time.
The relay is energized from the PCM (Powertrain Control Module) by grounding the circuit from the relay.
Check that the CRANK fuse gets power when the ignition switch is in the CRANK position. This fuse provides the PCM with the crank command from the ignition switch.

mountainmanjoe

we know his IGN A fuse works, otherwise it wouldn't have started when he bypassed the relay in his first post.

I was wrong about this. Bruce is right. 86 should have constant power. 85 receives a ground signal from the PCM.
This is why it's important to always follow the schematic.

He can also test his ignition switch by putting a meter on the CRANK fuse, and turning the key.