The Mystery Misfire

The dreaded P0171 code… If you've experienced it, just the mention likely gives you nightmares. If not - here's the rundown. P0171 is the automotive On-Board Diagnostics ( OBD ) code¹ for a lean condition on the engine. If the engine is running lean, it simply means that the air to fuel ratio is not optimized, and there's either too much air or not enough fuel. Before I get too far ahead here, let's set the scene.