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DTC B0856: 5-Volt Reference Out Of Range (SCM): Testing

WARNING: This page is about a different car, the 2000 Chevrolet Corvette. However, it is still accessible from the selected car via links, so may be relevant.
  1. If diagnostic system check was performed, go to next step. If diagnostic system check has not been performed, go to DIAGNOSTIC SYSTEM CHECK  under SELF-DIAGNOSTIC SYSTEM.
  2. Using scan tool, select SCM data display and monitor position sensor reference data. If scan tool does not indicate 4.0-5.2 volts, go to next step. If scan tool indicates 4.0-5.2 volts, go to step  9 .
  3. Turn ignition off. Disconnect seat adjuster motor connector C2, C3 and C4. See Figure . Turn ignition on. Using DVOM, measure voltage between ground and Purple wire connector terminal of seat adjuster motor connector while moving power seat switch. If voltage is 4.0-5.2 volts, go to next step. If voltage is not 4.0-5.2 volts, go to step  5 .
  4. Using DVOM, measure voltage between Purple and Black wire terminals of seat adjuster motor connector while moving power seat switch. If voltage is not 4.0-5.2 volts, go to step  6 . If voltage is 4.0-5.2 volts, go to step  7 .
  5. Check for open, short to ground or short to voltage in Purple wire between seat adjuster and SCM. If circuit is okay, go to step  8 . If faulty circuit is found and repaired, go to step  11 .
  6. Check for open or short to voltage in Black wire between seat adjuster and SCM. If circuit is okay, go to step  8 . If faulty circuit is found and repaired, go to step  11 .
  7. Replace the seat adjuster motor assembly. See SEAT ADJUSTER MOTORS under REMOVAL & INSTALLATION in POWER SEATS - CORVETTE article. After repairs, go to step  11 .
  8. Replace SCM. See SEAT CONTROL MODULE  under REMOVAL & INSTALLATION. After repairs, go to step  11 .
  9. Check seat adjuster motor position sensor circuits and connectors for intermittent malfunctions. See WIRING DIAGRAMS  . If problem circuit or connector is not found, go to next step. If problem circuit or connector is repaired, go to step  11 .
  10. Turn ignition off. Reconnect all disconnected components and connectors. Turn ignition on and clear any DTCs. Wait 2 seconds. If DTC B0856 does not reset as history, system is okay at this time. If DTC B0856 resets as history, go to step  8 .
  11. Turn ignition off. Reconnect all disconnected components and connectors. Turn ignition on and clear any DTCs. Recheck system operation. If system continues to malfunction, go to DIAGNOSTIC SYSTEM CHECK  under SELF-DIAGNOSTIC SYSTEM.
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