When the engine malfunction indicator lamp appears during startup on a Mercedes-Benz X253, the ME control unit may store fault code P261029.
This code refers to an unreliable engine shutdown time value or an invalid signal. According to the supplied repair documentation, the issue can be caused by software in the Instrument Cluster A1. Updating the cluster software may resolve the warning and prevent the fault from returning.
Confirm the Fault First
Before carrying out any programming work, connect the diagnostic system and read the ME control unit. Save:
- Fault code P261029
- Environmental or freeze-frame data
- The vehicle’s startup conditions
- Any additional stored faults
Confirm that the warning light appears specifically during vehicle startup. This step helps prevent unnecessary software updates when another fault may be responsible.
Prepare Xentry Correctly
The repair procedure requires the specified Xentry diagnostic environment. The supplied documentation refers to the 03/2019 Xentry version, connected to the internet with all available add-ons installed.
Before beginning, make sure:
- The vehicle battery is fully charged
- A suitable battery support unit is connected
- The diagnostic computer has stable internet access
- Xentry is updated with the required add-ons
- The vehicle remains undisturbed during programming
A voltage drop or interrupted communication during software programming can create additional faults, so preparation is essential.
Update Instrument Cluster A1 Software
Connect the vehicle to Xentry and select the Instrument Cluster A1 control unit. Program the software version specified in the documentation:
Instrument Cluster A1 software: 2539026309
Follow the diagnostic system’s on-screen instructions and do not switch off the ignition, disconnect the diagnostic equipment, or interrupt the vehicle power supply while the update is running.
After programming is complete, Xentry may request additional coding or configuration steps. Complete all required procedures before moving to the final checks.