Case Study: Software Fix for an Active CEL on a Kia/Hyundai with No Driveability Issues Sometimes, a check engine light (CEL) is a sign of an underlying mechanical fault. But in other cases, it’s simply a software issue—especially when the car is running perfectly. This case study highlights how a factory bulletin and proper diagnostics resolved an “all systems normal” CEL on a late-model Kia/Hyundai vehicle. The Complaint The customer brought the vehicle in with the check engine light illuminated. There were no driveability issues. The engine started and ran smoothly, with no hesitation, surging, or rough idle. Mileage at the time of service: 58,462 miles. Diagnostics Using the factory Kia/Hyundai GIT diagnostic platform, our technicians retrieved a fault code (P-code not specified in the notes). Engine management data inputs and outputs were tested and found to be functioning within factory spec. All major sensors reported correctly, and no issues were detected during physical or functional inspection. Research and Root Cause With no obvious mechanical or sensor failure, we turned to manufacturer support documentation. A search through Kia/Hyundai’s factory repair information revealed a service bulletin

Case Study: Software Fix for an Active CEL on a Kia/Hyundai with No Driveability Issues

Sometimes, a check engine light (CEL) is a sign of an underlying mechanical fault. But in other cases, it’s simply a software issue—especially when the car is running perfectly. This case study highlights how a factory bulletin and proper diagnostics resolved an “all systems normal” CEL on a late-model Kia/Hyundai vehicle.

Check Engine

The Complaint

The customer brought the vehicle in with the check engine light illuminated. There were no driveability issues. The engine started and ran smoothly, with no hesitation, surging, or rough idle. Mileage at the time of service: 58,462 miles.

Diagnostics

Using the factory Kia/Hyundai GIT diagnostic platform, our technicians retrieved a fault code (P-code not specified in the notes). Engine management data inputs and outputs were tested and found to be functioning within factory spec. All major sensors reported correctly, and no issues were detected during physical or functional inspection.

Research and Root Cause

With no obvious mechanical or sensor failure, we turned to manufacturer support documentation. A search through Kia/Hyundai’s factory repair information revealed a service bulletin specific to this fault code.

The bulletin explained that certain software versions in the ECU could trigger the CEL under specific—but benign—operating conditions. The solution: a software update to the vehicle’s ECM (engine control module).

The Fix

Using our GIT factory interface, we updated the vehicle’s software with the latest version as prescribed in the bulletin. Once the update was complete and the engine reinitialized, the check engine light turned off and remained off during all post-repair testing.

The vehicle was returned to the customer fully operational—and CEL-free.

Don’t Let a CEL Leave You Guessing

A check engine light doesn’t always mean something serious—but you’ll never know for sure without proper diagnostics. At CMD Automotive, we use factory tools and technical service bulletins to diagnose efficiently and accurately. Whether your vehicle needs a sensor, a solenoid, or just a software update, we’ll get it right.

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