Faulty instrument cluster bulb or LED for the Check Engine light.; Damaged wiring or connector between the engine control module and the instrument cluster.; Internal fault in the engine control module affecting the lamp driver circuit.; Communication error over the CAN (Controller Area Network) bus preventing lamp activation.; Low battery voltage or poor ground connection causing erratic lamp operation.; Aftermarket electronic installations interfering with the lamp circuit.

DTC codes / Mercedes-Benz codes / P1625

P1625 · Mercedes-BenzCheck Engine MIL

Q: What does code P1625 mean?

Check Engine MIL. This code indicates that the Mercedes-Benz engine control module has detected a condition requiring the Check Engine MIL (Malfunction Indicator Lamp) to be illuminated, often as a command from another module or a self-test failure within the ECU's lamp circuit. The computer is not reporting a specific drivability fault but rather a problem with the warning lamp activation path or a request from a related system.

This code indicates that the Mercedes-Benz engine control module has detected a condition requiring the Check Engine MIL (Malfunction Indicator Lamp) to be illuminated, often as a command from another module or a self-test failure within the ECU's lamp circuit. The computer is not reporting a specific drivability fault but rather a problem with the warning lamp activation path or a request from a related system.

SystemPowertrain

Code typeMercedes-Benz specific

SeverityLow

Fix difficultyIntermediate

AreaComputer and output circuits

Symptoms you may notice

The Check Engine light may be illuminated constantly or may fail to illuminate when the ignition is switched on.
Often no other symptoms besides the warning light, with the vehicle driving normally.
In some cases, the engine may enter limp mode if the ECU cannot confirm lamp operation.
The instrument cluster may show a bulb failure message or other warning indicators.
Intermittent illumination of the Check Engine light that does not correlate with engine performance.

Common causes, most likely first

Faulty instrument cluster bulb or LED for the Check Engine light.
Damaged wiring or connector between the engine control module and the instrument cluster.
Internal fault in the engine control module affecting the lamp driver circuit.
Communication error over the CAN (Controller Area Network) bus preventing lamp activation.
Low battery voltage or poor ground connection causing erratic lamp operation.
Aftermarket electronic installations interfering with the lamp circuit.

How to diagnose and fix it

Verify the Check Engine light operates during the instrument cluster self-test with the ignition on.
Inspect the instrument cluster for a failed bulb or LED and replace if necessary.
Check wiring and connectors between the ECU and cluster for corrosion, chafing, or loose pins.
Perform a battery and charging system test to rule out voltage-related issues.
Use a Mercedes-Benz-specific scan tool to read fault codes from all modules and check for communication errors.
If all external checks pass, test the ECU's lamp driver circuit with a multimeter or oscilloscope.
Replace the engine control module only after confirming an internal driver fault, and reprogram as needed.

When the Check Engine Light Itself Is the Fault

A P1625 code often appears after a dead battery or jump-start, when the ECU logs a lamp circuit fault due to voltage spikes.
Many technicians replace the instrument cluster unnecessarily when the real issue is a corroded ground connection behind the dashboard.
This code can be set by a communication failure over the CAN bus, so always check for stored codes in other modules before condemning the ECU.
On some Mercedes-Benz models, the Check Engine light is an LED soldered to the cluster circuit board, making bulb replacement a board-level repair.
The code does not always mean the lamp is burned out; it can indicate that the ECU cannot detect the lamp's resistance, which may be due to a wiring fault rather than the bulb itself.

Can I keep driving with P1625?

The vehicle is generally safe to drive because this code primarily affects the warning lamp circuit and not engine operation. However, avoid long trips until the issue is resolved, as the Check Engine light may not illuminate for future emissions-related faults, potentially masking a more serious problem.

Tools that help

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Guidance is general and written for Mercedes-Benz vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.