2000 Chevy Impala No Crank No Start Security Issues!

Hello there, im the 4th tech to look at this vehicle. so far ALL Powers/Grounds and Control check out good. i have no crank at ignition switch but when i was checking control from PCM to Crank Relay i had 12v and i used my test light to ground to check the circuit loaded in crank position and the vehicle woudl crank But as soon as i tool the ground from my test light away from the strat relay control wire it would Not crank using the key in start position. its an ex police cara and the AntiTheft light keeps flashing and I tired numerous attempts and Relarning and resetting it and still nothing! any help greatly appreaciated thank you again so much...

 

Any codes? Can you read crank request in scan data? With starter relay command

no codes and cant see crank request with scan tool that was used other day. owner talking about scraping it but i see its groudn side swithched and curious as when in crank position i have 12v on that control wire

Which control wire? One for the relay?

The security "password" is sent, from the Passlock Sensor, to the BCM through the yellow wire, at pin A3 connector 2. If this "password" is correct, the BCM sends the "OK" signal to the PCM, over the Class 2 Serial Data Bus. The PCM will not enable the starter if it does not receive the "OK".

With a scan tool, you should be able to access the BCM and monitor the Passlock "Password". The "Password" is simply a voltage.

With either a scan tool, or a voltage meter, check the voltage on the yellow wire. The voltage on the yellow wire of the passlock sensor (Pin A3, Connector 2 )should change as the key is turned, and released.

Also, if you have a scope, take a look at the activity on the Class 2 Serial Data Bus. Pin 2 of the DLC. It should a have 0 - 7 volt toggle, when messages are being sent.

The correct passlock password/voltage must be received by the BCM. And, then, the BCM must be able to transmit the "OK" via Class 2 data, to the PCM.

Yellow/Black Control from PCM to Relay

okay thank you will def check monday thank you again