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Old 03-18-2010, 01:24pm   #1
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Default HELP: Sometimes the vert won't start... VATS system issue?

Every once in a blue moon my vert won't start... everything works, all power, gauges sweep, etc, but when you go to engage the starter nothing happens. The first time it did this it started after a few times and once the starter actually engaged it fired right up like normal.

The 2nd time it did this I went inside and grabbed my 2nd set of keys and it fired right up. I looked at the "electrode" on my #1 set of keys and it looks to be in fine shape.

Af first I thought it may have been bad luck and the starter went bad as I had a similar issue when I let a buddy help me put the starter back on my Z06 post cam swap and he didn't tighten anything right... wire loosened up and I had the same type of "everything works, but no start" thing.

I'm guessing this is a VATS thing (what's that stand for again?... Vehicle Attempted Theft System?). Knock on wood it starts for me today @ work... will clean both keys w/ some rubbing alcohol. Might start keeping my 2nd key in the glovebox, but locked up.

Thoughts?

-Brian
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Old 03-18-2010, 02:05pm   #2
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Any codes on the DIC?
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Old 03-18-2010, 02:46pm   #3
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Default Reduced System Power

Never seen that one before.
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Old 03-18-2010, 03:56pm   #4
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Didn't pull codes... I recall hearing threads about it on CF... usually it's when the little chip on the key wears down or gets gunked up to the point the ignition switch doesn't register the signal to actually allow the car to start.

Had a similar issue w/ my old Mustang Cobra a long time ago when I went and got spare keys cut w/o knowing I had to have them programmed at the dealer. In that case the car would turnover and start then die immediately. W/o the key chip signal the car cut itself off.
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Old 03-18-2010, 04:20pm   #5
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There are a few components that can cause random no crank issues...

The starter (or solenoid attached to it)
The clutch pedal switch
The ignition switch
The Theft-Deterrent Relay


If you have a voltmeter, you can troubleshoot this, but the kicker is, you can only do it when the car doesn't start. If the car starts, then you will not find the problem, because everything obviously worked fine. For that reason, it can be difficult to isolate until the problem happens consistently.

So, where to start? Well, everything related to starter operation meets at the TDR (Theft Deterrent Relay). This relay is located just above the BCM (the big silver box) under the closeout panel in the pass. floorboard. There are 4 wires connected to this relay, and they are as follows:

Red (thick wire) - direct feed from battery. Hot at all times. This is protected by a 60a fuse, but it won't be blown since the problem is intermittent .

Purple - this is the output wire of the relay, that connects directly to your starter solenoid. Simply put, anytime this wire sees +12v, your starter motor "should" be cranking.

Then, the TDR control wires...

Yellow - this is the +12v side of the relay coil wiring. This originates at the battery, through a fuse, through the ignition switch, through the clutch pedal switch, and then ends up here.

Yellow with black stripe - this is the -12v (ground) wire to the relay coil. This wire comes from the BCM, and when no VATS or theft (alarm) intrusions are present, the BCM grounds this wire, and coupled with the +12v yellow wire, completes the circuit, energizes the relay, and energizes the purple wire to the starter.



So, in a logical method of narrowing things down, take the panel out of the floorboard, and leave your meter there, so you can quickly test things when it fails to crank. Next time the car will not crank, check things in this order.

1. Check the thick red wire. It should have +12v to a good ground at all times. (seat mounting bolt works good....the metal BCM case is NOT a good ground). You will probably find voltage there, so do this first, as it verifies you found a good ground point for the negative probe of your meter.

2. Check the purple wire in the same fashion, while clutch is depressed, and key is turned to start. If you find it has 12v, then it's looking like time for a new starter.

3. If TDR is not energizing (clicking) during an attempted start, the next thing to check is the yellow wire. It too, should be +12v to a good ground when trying to start. If it does not, then it's ignition switch, or clutch pedal switch. The easiest next step here would be to test the clutch pedal switch (just 2 wires, one in, one out, and should have continuity with pedal depressed). If that checks out, next suspect is ignition switch.

4. Finally, checking continuity to ground of the yellow/black wire. Set your meter to check continuity (ohms), and one probe on the yellow/black, the other to ground. You should find NO continuity when NOT trying to start the car. When trying to crank, the BCM should switch this wire to ground, and if it isn't doing that, then your VATS theory may be good.

5. So what if both yellow wires are doing what they should, but still no relay action? Bad relay.



Good luck, this can be frustrating to troubleshoot when it happens only occasionally.


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starter.jpg  


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Old 03-18-2010, 06:15pm   #6
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Brian, I had a similar problem on an 01 coupe. Turned out to be the ignition switch. Swapped it out and problem resolved. Bad contacts in the old switch are fairly common.
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Old 03-18-2010, 06:21pm   #7
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Thanks guys... Tom did you get that out of the servic manual? If not, man I thought I was technical w/ these cars... well done

When it oes this I do not get the "click" you spoke about.... and I know the sound exaclty. It just does nothing at all. So that means it's a clutch pedal witch or ignition switch.

@Hrdtop00 - What's involved in replacing the ignition switch? Can they re-key it to match the car or do I have to re-key the car?
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Old 03-18-2010, 06:34pm   #8
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Quote:
Originally Posted by Cobra4B View Post
Thanks guys... Tom did you get that out of the servic manual? If not, man I thought I was technical w/ these cars... well done

When it oes this I do not get the "click" you spoke about.... and I know the sound exaclty. It just does nothing at all. So that means it's a clutch pedal witch or ignition switch.
The relay not energizing could be either on the power (ign, clutch) side, or the ground (BCM) side of the relay coil. Both sides need to function in order for the relay to "click". You need to figure out on which side it's not happening to proceed..

The circuit drawing is out of the manual...the step by step advice was all me. I've been through it, I know it's frustrating to sort out all the possibles, so I posted the best way to methodically narrow down to the culprit.

This is the kind of stuff I work through for a living, but again, my frustration was getting it to fail consistently. It took me weeks before I could finally get it to fail when I had my meter out and ready to go. Only then could I determine what wasn't working. (in my case, the starter solenoid).



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Old 03-18-2010, 07:54pm   #9
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Quote:
Originally Posted by Cobra4B View Post
Thanks guys... Tom did you get that out of the servic manual? If not, man I thought I was technical w/ these cars... well done

When it oes this I do not get the "click" you spoke about.... and I know the sound exaclty. It just does nothing at all. So that means it's a clutch pedal witch or ignition switch.

@Hrdtop00 - What's involved in replacing the ignition switch? Can they re-key it to match the car or do I have to re-key the car?
You don't have to re-key it to match the car. It separates from the key cylinder.
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Old 03-18-2010, 09:17pm   #10
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Thanks guys... I'm just going to have to wait until it's good and broke to diagnose.
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Old 03-18-2010, 09:33pm   #11
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Quote:
Originally Posted by Cobra4B View Post
Thanks guys... I'm just going to have to wait until it's good and broke to diagnose.
Unfortunately, yes.

This is one of those problems you just can't throw parts at until it goes away. Your day of triumph will come when you turn the key 10 times and it doesn't crank 10 times.

If it's not a BCM issue, and you get stranded when it won't start, you can push start the car if need be. Yes it works, and yes I've done it. Might need to recruit a helper, but it doesn't take much to get a C5 rolling.

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Old 03-18-2010, 09:53pm   #12
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I've got AAA and a few buddies w/ trailers. Stinks that my dad has my trailer permanently now that he has our race car at his place in NC.

Any chance this was indeed a dirty key chip thingy?
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Old 03-18-2010, 09:56pm   #13
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Any chance this was indeed a dirty key chip thingy?
Of all the "common" causes of no start issues, that one would be bottom of list.

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Old 03-18-2010, 10:01pm   #14
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Just odd b/c the 2nd and final time it did this getting my 2nd key caused it to start instantly after 4ish attempts to start w/ the #1 key. Later in the day I tried the #1 key and it worked fine and it's worked fine since... I'm nearly daily driving the car.
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Old 03-18-2010, 10:23pm   #15
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Originally Posted by Cobra4B View Post
Just odd b/c the 2nd and final time it did this getting my 2nd key caused it to start instantly after 4ish attempts to start w/ the #1 key. Later in the day I tried the #1 key and it worked fine and it's worked fine since... I'm nearly daily driving the car.
Not saying it isn't possible, just saying more likely coincidence. I do not know what the exact cause of your problem is, I do know the most probable causes.

Gut feeling tells me the key isn't the issue. And you'd be very surprised at how reliable my gut feeling is. Here's your chance to prove me wrong.

But more importantly, I hope you can get it figured out soon and have a reliable car once again. Been there, done that, it's no fun.

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Old 03-18-2010, 10:25pm   #16
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Well.... it's only done it twice and I've been nearly DDing the car for two months now. That said my Z06 has never done this in the 7 years I've owned it.
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Old 03-19-2010, 07:39am   #17
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Thanks for all the info in here! Mine does this every now and then as well, and I had no idea where to start. Sucks being in a parking lot in a beautiful car - sitting there like an idiot not being able to leave!
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Old 05-31-2015, 02:47pm   #18
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Default 2004 Z06 same issue, looking for clarification.

New member here and completely dumbfounded

This is on a 2004 Z06 with a Stock GM Battery.

Here are the chain of events and t-shooting:
• Turn the key and all power to the car worked fine.
• Car would not engage the starter. (No solenoid click)
• TDR never clicks, however a relay on the fuse box does.
• NOT an intermittent issue.

Troubleshooting:
• No codes appearing.
• Tried 2nd key that does not get used much, same result.
• Checked resistance on both keys and cleaned them.
• Bypassed clutch safety switch.
• Ensured Battery was/is good and fully charged. (Tested at 2 Parts stores)
• Swapped battery with a known good one for testing.
• Checked every fuse in car for continuity.
• Followed every step in this post.
• The TDR:
Is not clicking.
Red wire always 12v.
Purple wire doesn’t ever gets 12v.
Yellow wire 12v when attempting to start.
Yellow/black wire NEVER has continuity, attempting to crank or
not.
Cleaned all contacts on TDR relay.

• Starter WILL engage manually crossing posts with a screwdriver, however car will try to run, then stops. (I only did this once) 

I obviously don't want to throw parts at the car, however I am torn between the TDR and Ignition Switch. And I may be off on that!

Is there an effective way to bench test the TDR?

Thanks in advance!

Barry
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Old 05-31-2015, 04:20pm   #19
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Quote:
Originally Posted by Barry B View Post
• The TDR:
Is not clicking.
Red wire always 12v. This is good
Purple wire doesn’t ever gets 12v. This is expected...If/when that wire does see +12v, your starter should work
Yellow wire 12v when attempting to start. This is good
Yellow/black wire NEVER has continuity, attempting to crank or
not. This is not good
Barry, welcome to the forum, and good job on the troubleshooting thus far, you've got it pretty well narrowed down.

What I would do next is tap into that yellow/black wire coming out of the TDR, and connect a jumper wire from it to a verified good ground point. (as I recall, not easy to find in that area...maybe a seat mounting bolt?). Leave everything connected to the TDR as normal.

Now depress the clutch, turn the key and attempt to start the car. This is just a test, not a fix, and all you're concerned with at this point is whether the starter cranks or not.

-If the starter still doesn't turn over, I'd say your TDR is bad.
-If it does crank for this test, then it seems the BCM is inhibiting starting by not switching that yel/blk wire to ground during starting. You've already indicated this may be the case, this just proves it.
If it is the latter, it's possible the engine won't fire and run due to other protection features of the BCM, but you've at least narrowed it down to this. Though I'd think if the BCM were inhibiting start, there'd be other indicators...Security light or BCM codes, not sure.

Have you ever had any water intrusion in the pass. footwell (wet floor), such as from a clogged a/c drain?
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Old 05-31-2015, 04:55pm   #20
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Thank you for the welcome

Never have I SEEN any water there and I see no signs of any corrosion, but will double check.
I will go try this suggestion and follow up shortly with the results.
The ground spot I have been using is below the glove box and to the left where that piece of carpet that always falls down covering 2 pieces of metal is located. I connect the neg probe from the voltmeter to it.
Works great

Barry



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Barry, welcome to the forum, and good job on the troubleshooting thus far, you've got it pretty well narrowed down.

What I would do next is tap into that yellow/black wire coming out of the TDR, and connect a jumper wire from it to a verified good ground point. (as I recall, not easy to find in that area...maybe a seat mounting bolt?). Leave everything connected to the TDR as normal.

Now depress the clutch, turn the key and attempt to start the car. This is just a test, not a fix, and all you're concerned with at this point is whether the starter cranks or not.

-If the starter still doesn't turn over, I'd say your TDR is bad.
-If it does crank for this test, then it seems the BCM is inhibiting starting by not switching that yel/blk wire to ground during starting. You've already indicated this may be the case, this just proves it.
If it is the latter, it's possible the engine won't fire and run due to other protection features of the BCM, but you've at least narrowed it down to this. Though I'd think if the BCM were inhibiting start, there'd be other indicators...Security light or BCM codes, not sure.

Have you ever had any water intrusion in the pass. footwell (wet floor), such as from a clogged a/c drain?
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