Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Code 51
On AB and AN bodies, DRB displays O2S STAYS BELOW CENTER (LEAN). Condition is: oxygen sensor input indicates lean air/fuel ratio during engine operation.
On BR body, DRB displays SYSTEM LEAN L-IDLE ADAP AT RICH LIMIT. Condition is: oxygen sensor signal input indicates lean air/fuel ratio condition at left O2S during engine operation. If vehicle is equipped with dual O2S, DRB will identify left or right O2S.
On BR body, DRB displays SYSTEM LEAN R-IDLE ADAP AT RICH LIMIT. Condition is: oxygen sensor signal input indicates lean air/fuel ratio condition at right O2S during engine operation. If vehicle is equipped with dual O2S, DRB will identify left or right O2S.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.