09 impala engine runs with key off
First off you need to read how this works . BCM - body control module is in fail- safe mode more then likely . The ingition switch is a input to the BCM . The BCM turns on relays to turn vehicle systems on . If something happens the system will fail safe to last commands by the BCM .
The body control system consists of the body control module (BCM), communications, and various input and outputs. Some inputs, outputs and messages require other modules to interact with the BCM. The BCM also has discrete input and output terminals to control the vehicle's body functions. Battery positive voltage is provided to the BCM from the BCM fuse in the underhood fuse block. The module has two grounds at G 202 as well as one directly to the vehicle battery. The BCM is wired to the GMLAN High speed serial data buss and the GMLAN Low speed serial data buss and acts as a gateway between them. If the BCM does not communicate the vehicle will not start due to the inability of the engine/powertrain control module (ECM/PCM) and vehicle theft deterrent (VTD) control module to communicate without the BCM providing the gateway function.
Power Mode Master
This vehicle body control module (BCM) functions as the power mode master (PMM). The ignition switch is a low current switch with multiple discrete ignition switch signals to the PMM for determination the power mode that will be sent over the serial data circuits to the other modules that need this information, and so the PMM will activate relays and other direct outputs of the PMM as needed. Refer to Power Mode Description and Operation for a complete description of power mode functions.
Relay Controlled Power Mode
The body control module (BCM) uses the discrete ignition switch inputs Off/Run/Crank Voltage, Accessory Voltage, and Ignition 1 Voltage, to distinguish the correct power mode. The BCM, after determining the desired power mode, will activate the appropriate relays for that power mode.
The RAP relay remains on for a timed period after the Ignition key is removed. Refer to Retained Accessory Power Description and Operation for more information on the retained accessory power (RAP) function.
You mite want to thing about taking your vehicle to a qualified repair shop. Hooking up a professional or factory scanner to view input data to the BCM ,plus checking for DTC'S - diagnostic trouble codes in the BCM , autozone , advance part stores can not read codes in the BCM .
11 hours ago