Of course, one of the most serious warning lights that can turn on is the check engine light. In most cases, the check engine light is only triggered by a minor issue, such as a loose fuel cap or worn-out spark plugs. The NT301 can quickly retrieve a diagnostic trouble code from your vehicle’s engine control module to identify the current problem. Most people will rush to their local repair shop whenever they see their check engine light turn on. It only takes one sensor to detect a problem, activate the check engine light, and produce a diagnostic trouble code.