GM's Passkey III system has no start wire in the ignition harness. The BCM needs to see a certain sequence with the accessory and ignition wire to start the vehicle. The BCM monitors the ignition wires and starts when (ACC engages, then both ACC and IGN and finally drops ACC).
- Here's how to wire.
- Iign. + (Diode)to relay 86 & 87a
- 30 to acc. wire
- 85 to switched ground
When there is ground to relay start as normal. When no ground relay matains voltage from the ign. to the acc. (no start).
To do a Starter Kill Normally Closed (Ground When Armed).
- Ign. + (Diode)to relay 86 & 87
- 30 to acc. wire
- 85 to switched GWA
TO: lurch228....... If what you say is true about the start circuit being triggered by seeing ignition, then dropping out the ACC then why is there a START wire at the ignition switch? Example: GMC envoy, CHEV Tblazer, and my SAAB 9-7X.
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thetopinstaller
Some of those vehicles with the start wire were still using Passlock II for the immobilizer and some were using Passkey 3 which usually doesn't have a start wire. Some may have a start wire that's only used by the BCM for start detection but won't be used for remote start.
The Passlock II is a resistor based system and Passkey 3 is a transponder based system. Some vehicles have both with Passkey 3+ that uses resistor and transponder.
On the vehicles that don't use the start wire, the BCM needs to see ACC first, then ACC with IGN and finally ACC drop off to engage the starter.
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Practically all new GM's use this setup now with no start wire on the switch. The Trailblazer/Envoy hasn't been made in years.
I will have to give this a try as i have messed with ways to do this and none have worked well...
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Mike M2
Tech Manager
CS Dealer Services
This method is for vehicles that don't have a starter wire and the key is typically on the dash not the column that use the ACC. drop out to start. This won't work for any vehicle that has a heavy guage starter wire that goes out to the starter. And if there is a small guage starter wire that the BCM uses to engauge the start cycle you will need to use the standard starter kill method.