Circuit Description

WARNING: This page is about a different car, the 2000 Isuzu Hombre. However, it is still accessible from the selected car via links, so may be relevant.

A Class II serial data communications system is used to allow communication between Vehicle Control Module (VCM) and VTD system. VTD sends a Vehicle Security Password (VSP) when ignition 1 input becomes active, and includes its source Identification (ID). The VSP includes either a fuel continue or fuel disable password.

When Pass-Lock® portion of VTD has sensed the proper operation of the ignition switch and lock, VTD system transmits a password to VCM. VCM enables fuel delivery if password matches 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 enable mode. VCM remains in fail enable mode for current and future ignition cycles, until fault is corrected and 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 an invalid password or no password before fuel disable decision point, VCM disables fuel delivery. Fuel disable decision point occurs at about 300 RPM during engine cranking mode.

Conditions required to set DTC are:

VCM established communications and received VSP during current ignition cycle from VTD control module.
VCM has not detected communications and/or has not received NODE A live/SOH messages from VTD control module.
VCM cannot establish communications with VTD control module and has not received a valid password before fuel disable decision point.