Dgriff

Just digesting your last reply....So I gather by your message, there is a realistic real world chance of uncontrolled 12V finding its way onto that circuit? Out of curiosity are we talking an internal ECU situation or external? Can you not incorporate a test button with associated stop/go LED (or a globe needing more than 20-30mA to fire up) to interrogate the K line before attaching scanner to computer and from a wiring point of view, before the driver chip?