Note. For circuit reference, see WIRING DIAGRAMS - 4.3L article.
Circuit Description
A Class II serial data circuit is used in communication between VCM and Vehicle Theft Deterrent (VTD) system. VTD sends a Vehicle Security Password (VSP) when ignition 1 input becomes active and includes its source ID. The VSP includes either a fuel continue or fuel disable password.
When Pass-Lock(R) portion of VTD system has sensed the proper operation of the ignition switch and lock, the system transmits a password to the VCM. VCM enables fuel delivery if this password matches the password stored in VCM's memory.
If communication is lost or a VTD failure occurs (during an ignition cycle that VCM has enabled fuel), VCM will enter a fail-safe/fail enable mode. VCM remains in fail enable mode for the current and future ignition cycles, until fault is corrected and a valid password is received, or until battery power is removed. If battery power is removed while VCM is in fail enable mode, VCM disables fuel delivery. Vehicle will not start or will start then stall.
When VCM receives a invalid password or no password before the fuel disable decision point, VCM disables fuel delivery. Fuel disable decision point occurs at about 300 RPM during engine crank mode.
Conditions for setting DTC
- VCM has established communications and received VSP during current ignition cycle from VTD control module.
- VCM cannot establish communications with VTD control module and has not received a valid password before fuel disable decision point.