Body, generic

B0850 Left Brake Lamp Circuit

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modeNo

B0850 cannot be confirmed from any open source – J2012 tables, OEM documentation and NHTSA bulletins omit it. The title covers the left stop lamp. In Saab's 9-3 (type 9440) the rear electrical centre checks it while braking under its own number B3445: below 50 mA it records an open circuit (04), and once current tops 6 A for over 6 ms a short to ground (02), shutting the output down. The third, high-level brake light is logged separately there (B3884). FMVSS 108 makes stop lamps mandatory and defines the high-mounted lamp as a steady stop warning visible through other vehicles. HELLA lists bulbs, holders, fuses and plug connections as the first checks. A missing brake light weakens the warning to following drivers and should be repaired at once. Right side: B0851.

Likely causes

Left stop-lamp bulb or filament failed
Corroded bulb holder in the tail lamp
Open or grounded wire to the left tail lamp
Stop-lamp output of the rear module faulty

Symptoms

  • Left brake light stays dark when braking, warning shown
  • Weaker warning to following traffic; repair before further driving
  • Tail light on the same side may also be affected with combined bulbs

Repair estimate

DifficultyEasyDIY possible
Parts and labour€5–250
Time0.2–1.5 h

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

Parts involved

left brake lampbody control module

Related codes

B0851B0235

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