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Home >> Cadillac >> 1999 >> Escalade >> Repair and Diagnosis >> External Pages >> Different car >> Section 4 (Anti-Theft System - Escalade, Express, Pickup, SAVANA, TAHOE & YUKON DENALI) >> Diagnostic Tests >> DTC U1255: Class 2 Communication Malfunction >> Diagnostic Procedure

Diagnostic Procedure

WARNING: This page does not describe the selected car, but rather 15 other vehicles, including the 2000 GMC Yukon, 2000 GMC Savana Special, 2000 GMC Savana Camper Special, 2000 GMC Savana, and 2000 GMC Pickup. However, it is still accessible from the selected car via links, so may be relevant.
  1. Turn ignition on. Using scan tool, attempt to communicate with VCM. If communication exists, go to next step. If no communication is possible, diagnose DLC. See DATA LINK CONNECTORS article in WIRING DIAGRAMS. After repairs, go to step  3.
  2. Turn ignition off. Disconnect 16-pin Passlock™ module connector. Measure resistance of Purple wire between Passlock™ module harness connector terminal B4 and DLC terminal No. 2. See Figure. If resistance is less than 10 ohms, replace Passlock™ module. See PASSLOCK™ MODULE  under REMOVAL & INSTALLATION. After repairs, go to next step. If resistance is 10 ohms or more, repair open in Purple wire. After repairs, go to next step.
  3. Turn ignition off. Reconnect all connectors and components. Turn ignition on. Using scan tool, clear all DTCs.
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