Andon (Stop the Line)

A defect caught where it is made has one cause and an obvious fix; the same defect found three stations later is buried under work built on top of it, and the person who could explain it has moved on. Pressure to keep the line moving makes each worker discount what they saw and assume someone downstream will catch it. Toyota's jidoka moved the decision into the station: first a loom that stopped itself when a thread broke, later a cord any operator can pull to halt the line and light the andon board. The stop is not the point; it forces the abnormality to be examined while the evidence is still fresh.

At the old GM plant in Fremont, California, which closed in 1982, workers said the rule was that the line must never stop, and one recalled that stopping it could get you fired. When GM and Toyota reopened it as NUMMI, workers got an andon cord: a pull summoned team leaders, and the line stopped only if they could not fix the problem. NUMMI's defect rate was among the best in America from the start, with near-perfect quality ratings within months of the first car in December 1984.

Throughput Pressure: every stop costs output, and where a team is judged on throughput, pulling the cord becomes a cost someone has to justify, so a cord that fires often or falsely teaches people to route around it.