Body, generic

B0840 Left Rear Turn Signal Circuit

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modeNo

Neither J2012 extracts nor any OEM or NHTSA publication name B0840; its use is unproven. The title concerns the left rear indicator. In the 2003–2012 Saab 9-3 the rear electrical centre supervises this lamp under the number B0530: an open lamp (04) or a short to ground (02) shows up as a warning message and the remaining indicators flashing at double speed, which is exactly the pilot-indicator behaviour FMVSS 108 permits for a failed turn lamp. HELLA notes that modern rear lamps are driven by body or lighting control units and may consist of LED segments, so diagnosis should include fault codes, connectors and the supply to the lamp unit. A failed rear indicator hides lane changes from following traffic. Right rear: B0841.

Likely causes

Rear indicator bulb or LED segment failed
Corroded plug or bulb carrier in the rear lamp
Wire break in the boot lid or tailgate harness
Rear electrical centre output faulty

Symptoms

  • Indicators flash at double speed when signalling left
  • Left rear indicator dark, warning message shown
  • Lane changes not visible to following traffic; repair promptly

Repair estimate

DifficultyEasyDIY possible
Parts and labour€5–300
Time0.2–1.5 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

left rear turn signalbody control module

Related codes

B0841B0830B0850

References: saabwisonline.com, saabwisonline.com, law.cornell.edu, hella.com.