P1682

P1682 is the Driven Power 2 (also called Ignition Voltage 2 on some calibrations) circuit code — the PCM monitors a secondary switched-ignition feed (typically pin labeled IGN-E or Driven Power 2 on E40, E67, and later E38/E92 PCMs) that must be at battery voltage whenever the primary ignition feed is at battery voltage. When the two feeds disagree by more than approximately 2V for over 1 second, P1682 sets. Cheapest-first: locate the PCM connector with the Driven Power 2 pin (consult the wiring diagram for the specific PCM — on E40, it's typically C1 pin 71; on E67, C2 pin 4 area) and backprobe with a DMM key-on; you should see steady battery voltage that drops with the ignition switch. If the voltage is low or absent, trace upstream to the underhood fuse block — the Ign 1 and Ign 2 fuses share a common feed but split at the bus, and a corroded fuse-block contact will pass one feed while starving the other. The expensive misdiagnosis: replacing the PCM ($1200+ programmed) when the actual fault is a green-corroded pin in the underhood fuse block.

Vehicle-specific patterns: 2004-2007 Silverado/Sierra/Tahoe/Yukon/Suburban 4.8L/5.3L/6.0L with E40 PCM is the classic P1682 truck — the underhood fuse block develops solder cracks on the Ign 2 bus, documented in PIP4055 (the fix is fuse block replacement or careful resolder). 2007-2013 Silverado/Sierra 5.3L/6.0L with E38 PCM sees P1682 from corrosion at the C2 connector (the gray one) where road salt enters through a poorly seated bulkhead grommet. 2006-2009 Trailblazer/Envoy 5.3L LH6 throws P1682 from the same fuse-block failure pattern. 2008-2010 Cobalt SS 2.0L Turbo with E67 gets P1682 from the underhood relay center developing high resistance on the secondary ignition relay contacts. Estimated repair: $40 to $1400.