trailblazer remote start issues when cold

I have a 2006 Trailblazer LT, I installed a viper 5901 last month. But now I am noticing that it will not start if is cold out (like a maybe 20 and below, so it deffinently doesn't for when its 0 out, like now). I just replaced the battery and it didn't make a difference. I am using the virtual tac that I programed by holding down the button, I tried changing the crank time, heck in even tried the wait to start feature for 15 sec. Nothing changed, it cranks like it can start but just dies imediatly. Any suggestions?

I am pretty sure your vehicle has factory over-crank protection. To test this, start it with the key, when the engine starts to run the starter should disengage even though you are holding it to the start position. If it continues to crank release the key quickly and I would suggest using a hard wired tachometer connection.

To use virtual tach you do not change anything in the programming menu...pressing the button within 5 seconds of starting with a key applies only if you used a hard wired tach connection.

Anytime I do a GM vehicle with factory over crank protection I set the system to use voltage sensing and set the crank time to 2 seconds. Since the vehicle disengages the starter on it's own there is no worry about over crank. You would have to program 2 settings in the menu...

Menu 3, option 2: set to option 2, voltage sensing
and
Menu 3, option 3: set to option 8 (2 seconds crank time)

Your truck will probably never need the full 2 seconds of crank, but since the starter disengages itself the extra time is there for a 'worst-case' scenario.

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Installer, IT support, and FFL. I need less hobbies.

I beilive you are right about the over crank protection but I will check to make sure. I will also change the settings... Thanks for the quick reply.

run an actual tach wire. best advice i can give. i've done countless of those vehicles and always ran a tach to either the cluster or to the pcm and haven't ever seen any of them back with issues.

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A DMM is a beautiful thing.

MECP Advanced Installer Certified.

run a tach wire to the white wire in the harness that runs left to right under the ign switch wiring, these vehicles have issues going tachless, tach wires easy to get to

The issue is that when cold out, the truck is design such that the alternator does not come "online" for several seconds after start, this is to keep load off of a cold engine so it won't stall- so if  you program your remote start as voltage sense. the remote starter starts the truck, then looks for increased voltage, then when it does not see it, it shuts itself off and tries again- because it thinks it did not start, because of the delay in the alternator. 

Bottom line, always go with hard-wired tach in Trailblazers to monitor engine.

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Brcidd - Engineer That Does Remote Starter Installs on the side.

I set up the voltage sensing and tried it this morning when it was -1 degrees out and the trailblazer started right up no problem. If the problems persist I will be sure to run a tach wire. Thanks for all your help guys!

Glad to hear it's working!  I will not disagree that an actual tach connection is the absolute best way.  But I have never heard of an alternator 'not coming online when cold'...although I am NOT a mechanic so I can't say for sure.  I use DEI products and have been doing automatic transmission GM trucks this way ever since I realized they had factory over crank protection.  Not one has ever come back. 

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Installer, IT support, and FFL. I need less hobbies.

Below is  a comment I saved from another forum- and I do remember looking it up in the service manual at one time to confirm....

Just heard thru the grape-vine that the voltage jump after a (very) cold startup is perfectly normal for the GMT360 chassis. Apparently, the PCM takes the alternator 'off-line' for 10-30sec to lessen the load on an extremely cold engine. This explains the ~10 to 14.4VDC jump you see on the dash gauge and see/hear from the dash lights and heater blower. Basically, you run on battery power alone for a few seconds after a stone cold startup

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Brcidd - Engineer That Does Remote Starter Installs on the side.

brcidd wrote:

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Just heard thru the grape-vine that the voltage jump after a (very) cold startup is perfectly normal for the GMT360 chassis. Apparently, the PCM takes the alternator 'off-line' for 10-30sec to lessen the load on an extremely cold engine. This explains the ~10 to 14.4VDC jump you see on the dash gauge and see/hear from the dash lights and heater blower. Basically, you run on battery power alone for a few seconds after a stone cold startup

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Great information, THANKS!

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Installer, IT support, and FFL. I need less hobbies.

brcidd is correct which is why i have always used tach on trailblazers/envoy etc. its a very easy wire to get at in that large main harness under drivers side dash just be sure to meter as there are a bunch of whites in there it is in the middle top of the harness

Again, I have never had any come backs with voltage sensing on those trucks. Must not get cold enough here in Southern New Jersey to have it affect it. But now that I am aware of it, they will all get tach connections from here on out. Thanks again.

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Installer, IT support, and FFL. I need less hobbies.

I had three comebacks- all after a real cold spell- That's when I started researching the issue....Then I was able to fix two of them- the third guy said he'd live with it.....from then on- it has been tach hook-ups.

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Brcidd - Engineer That Does Remote Starter Installs on the side.