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DTC L209: OSM No. 9 Communications Problem: Description

Code L209 indicates that the BCM has been unable to correctly communicate information to OSM No. 9. This fault could affect the operation of the right front side marker, right low beam, left front side marker and the left low beam.

NOTE: The following numbered steps refer to circled numbers on diagnostic chart. See Fig 1. For circuit identification, see Fig 2.
  1. If you were not directed here from Lighting Chart A-1, a wrong diagnosis could result if not performed first. See LIGHTING CHART A-1 in SELF-DIAGNOSTICS article in ENGINE PERFORMANCE.
  2. Visually inspect cavities and pins of the OSM for obvious connection problems.
  3. Checks for proper power supply to the OSM.
  4. Checks for proper ground to the OSM.
  5. Checks for proper OSM address identification.
  6. Hazard flashers will increase data line activity. Typical voltages will be between zero and 5 volts and will be constantly fluctuating. This will help identify whether the OSM or the data line is the problem.
NOTE: When all diagnosis and repairs are completed, clear codes and verify operation.
Fig 1: DTC L209: OSM No. 9 Communications Problem Flow Chart
G00100627Courtesy of GENERAL MOTORS CORP.
Fig 2: DTC L209: OSM No. 9 Communications Problem Flow Chart Circuit
G00100628Courtesy of GENERAL MOTORS CORP.