If, after parked regen, the check engine lamp or MIL remains illuminated, the fault condition should be diagnosed by a ______.

• A. Detroit Diesel Service representative
• B. Local mechanic
• C. Owner
• D. Factory service manual

Answer: (A)

When the MIL stays on after a parked regen, specialized diagnostic access is needed. A Detroit Diesel Service representative has the factory tools, software, and up-to-date service information required to read and interpret the engine’s fault codes correctly, verify the regen procedure, and determine the exact cause of the persistent warning. They can check for issues in sensors, exhaust aftertreatment, or calibration that a generic mechanic or the owner might not be able to diagnose accurately, and they can apply the correct factory follow-up actions or software updates and confirm the fix with proper testing. While the factory service manual is a valuable reference for troubleshooting steps, it does not substitute for the diagnostic capability and authorized service access that a factory representative provides.