2009 GMC Envoy Logo
i
ingrid Posted on Jan 16, 2015
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I have a 2009 g envoy and when I turn my key it wont do anything.replaced the ignition switch and it has worked fine for about 5 months and now it is doing the same thing sometimes it will start right

Replaced ignition switch doing it again after 5 months with new switch

1 Answer

Jeff Armer

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  • GMC Master 15,575 Answers
  • Posted on Jan 16, 2015
Jeff Armer
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On GM vehicles starting back in mid 2000's , maybe even before that. They started using inputs to the body control module from the ignition switch, from there the BCM controls all vehicle systems .
Power Mode Description and Operation
Serial Data Power Mode
On vehicles that have several control modules connected by serial data circuits, one module is the power mode master (PMM). On this vehicle the PMM is the body control module (BCM). The BCM uses 3 signals from the ignition switch. These are the Ignition 0, Ignition 1, and Accessory.
To determine the correct power mode the BCM uses:
?€¢
The state of these signals


?€¢
The sequence of switch closures received by the BCM


?€¢
The status of the engine run flag

The chart indicates the power modes detected and transmitted by the BCM:

Correct Ignition Switch Inputs
Ignition Key Position

Power Mode Parameter

Engine Running

Sampled Ignition Signal State

Accessory

Ignition 1

Ignition 0
OFF
Off-Awake or RAP
No
Inactive
Off
Off
UNLOCK
Unlock or RAP Unlock
No
Inactive
Off
On
ACC
Accessory
No
Active
Off
On
ON
Run
No
Active
On
On
START
Crank
No
Inactive
On
On
ON
Run
Yes
Active
On
On
Fail-safe Operation
Since the operation of the vehicle systems depends on the power mode, there is a fail-safe plan in place should the body control module (BCM) fail to send a power mode message. The fail-safe plan covers modules with discrete ignition signal inputs as well as those modules using exclusively serial data control of power mode.
Serial Data Messages The modules that depend exclusively on serial data messages for power modes stay in the state dictated by the last valid BCM message until they receive the engine status from the powertrain control module (PCM). If the BCM fails, the modules monitor the serial data circuit for the engine run flag serial data. If the engine run flag serial data is true, indicating that the engine is running, the modules fail-safe to Run. In this state the modules and their subsystems can support all operator requirements. If the engine run flag serial data is false, indicating that the engine is not running, the modules fail-safe to OFF-AWAKE. In this state the modules are constantly checking for a change status message on the serial data circuits and can respond to both local inputs and serial data inputs from other modules on the vehicle.
Discrete Ignition Signals Those modules that have discrete ignition signal inputs also remain in the state dictated by the last valid BCM message received on the serial data circuits. They then check the state of their discrete ignition input to determine the current valid state. If the discrete ignition input is active, B+, the modules will fail-safe to the RUN power mode. If the discrete ignition input is not active, open or 0 voltage, the modules will fail-safe to OFF-AWAKE. In this state the modules are constantly checking for a change status message on the serial data circuits and can respond to both local inputs and serial data inputs from other modules on the vehicle.
You would need a scan tool that can read data from the BCM . What may be the problem is a lose connector , these pin's at connectors are tiny and doesn't take much for one to become lose.

5 Related Answers

Anonymous

  • 1 Answer
  • Posted on Jun 30, 2009

SOURCE: 1997 GMC Jimmy sometimes will not start

I had a similar problem several years ago on my 97 Jimmy. There is a switch in the steering column that had gone bad, had to be replaced and no problem since. The symptons sounded just like yours. My trusted mechanic found the problem after a lot of testing and fixed it.

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Philip Armitage

  • 437 Answers
  • Posted on Oct 09, 2009

SOURCE: 2006 GMC ENVOY starter not turning over, with ignition switch on.

the ignition switch is a problem with these vehicles so that would be my first call.

JIMMY

  • 1374 Answers
  • Posted on Apr 14, 2010

SOURCE: 2002 GMC Envoy, i put the key in ignition and

Ignition switch and neutral safety switch. Next time it happens wiggle thekeys in the ignition switch and try to restart.If it starts its probably the ignition switch. Then locate neutral safety switch on brake pedal and put meter on B+ wire from switch to starter relay and see if you get B+ on the would -be- crank. Next locate B+ wire from starter relay to starter hook a meter to it and see if you get B+ on the would -be crank.
Where ever B+ is missing is your problem.

Anonymous

  • 15 Answers
  • Posted on Dec 08, 2010

SOURCE: I replaced fuel pump and

not knowing what kind of vehicle it is it is hard to tell. some gm cars and trucks have oil sending units that will not allow the vehicle to start unless it has oil pressure. they start going out and sometimes they start and sometimes they won"t.

Freddy

  • 1311 Answers
  • Posted on Mar 12, 2011

SOURCE: key will turn and all

Check relay #47 in the underhood fuse panel, this relay is for the starter.

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Please accept this answer to remove the multiple occurances of this same question from the work queue.
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