B0851 code meaning
Right Brake Lamp Circuit
What B0851 means
Published J2012 tables skip B0851, and service literature and NHTSA filings never cite it either. The title names the right stop-lamp circuit. The GM-developed Saab 9-3 tests this lamp whenever the brake light is on and stores B3878 04 once the right lamp draws less than 50 mA; the high-mounted lamp is judged separately under B3884 with a lower limit of 20 mA. If both sides and the third lamp go dark together, the cause usually lies upstream, at the brake light switch or a shared fuse, not in one lamp circuit. For today's networked rear lamps HELLA names failed LED segments and faulty plugs as typical findings. FMVSS 108 requires working stop lamps on every car. Repair without delay; left side: B0850.
B0851 at a glance
- Check engine lightUsually not
- Emissions testNot an emissions code
- Limp modeNot expected
- Repair difficultyEasy, DIY possible
- Typical labor0.2 to 1.5 hours
- Clears after repairWhen cleared with a scanner
Symptoms of B0851
- Right brake light dark while the left one and the third lamp work
- Brake light warning in the display
- Reduced braking signal to following drivers; repair at once
Common causes of B0851
- Most likelyRight stop-lamp bulb or LED segment failed
- PossibleLoose or corroded plug at the right tail lamp
- PossibleWire to the right tail lamp broken
- Less likelyLamp driver in the rear module faulty
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Right brake lampBody control module
What each part of B0851 means
| B | Body system: airbags, seat belts, power seats, lights and climate control. |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 51 | The exact fault in that area. |
What to do next
- Note B0851 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about B0851
What does B0851 mean?
B0851 means "Right Brake Lamp Circuit". Published J2012 tables skip B0851, and service literature and NHTSA filings never cite it either. It is a generic code, so it means the same on every make.
Is it safe to drive with B0851?
B0851 does not normally turn on the check engine light by itself. Watch for the symptoms above and have it checked soon.
Will B0851 fail an emissions test?
B0851 is not an emissions code, so on its own it usually does not fail an emissions test. Other stored codes or a lit check engine light still can.
How hard is B0851 to fix?
Difficulty: easy. A typical repair takes 0.2 to 1.5 hours of work. A careful DIY repair is possible with basic tools and a scanner.
Will B0851 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.