Understanding your Mercedes-Benz is crucial for its upkeep, and interpreting diagnostic codes is a vital part of that process. While modern Mercedes-Benz vehicles utilize sophisticated OBD-II code readers, older models offer a unique, if somewhat cryptic, method of displaying diagnostic trouble codes. This guide will walk you through the process of reading and understanding these codes on your classic Mercedes-Benz, essentially acting as a “code reader” yourself.
Reading Diagnostic Codes on Older Mercedes-Benz: The Blink Method
For archive purposes and for owners of older Mercedes-Benz models, it’s useful to understand the built-in diagnostic system. This system uses a diagnostic port and an LED to blink out error codes. Here’s how to access these codes:
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Engine Off, Ignition On: Ensure your engine is turned off. Then, turn your ignition switch to position #2. This position turns on the car’s electrical systems without starting the engine.
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Engage the Diagnostic Switch: Locate the diagnostic port in your Mercedes-Benz. Depress the switch at this port for approximately one second, and then release it.
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Count the LED Blinks: Carefully observe the LED light. It will begin to blink. Count the number of blinks before the LED stays on solid (always on). This sequence of blinks represents a diagnostic code.
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Check for Additional Faults: To see if there are any other stored fault codes, depress the switch again. The system displays faults in descending order. If no further faults are stored, the first fault code will repeat. Record each code (number of blinks) for later interpretation.
Resetting the Check Engine Light
After identifying and addressing the issue indicated by the diagnostic code, you’ll likely want to reset the check engine light. This system allows for a reset procedure as well:
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Solid LED Indication: After reading the codes, and within 20 seconds of the LED turning solid/always on, prepare to reset.
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Depress and Hold the Switch: Depress the diagnostic switch again and hold it for 6 to 10 seconds. Then, release the switch.
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Observe the LED Blink: The LED should blink once and then go to solid/always on, confirming the reset command has been received.
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Turn Ignition Off and Restart: Turn the ignition switch off completely. Then, restart your Mercedes-Benz. The check engine light should now be off, assuming the underlying problem has been correctly resolved.
Mercedes-Benz Diagnostic Trouble Codes: Blink Code to Fault Interpretation
Here is a list of the blink codes and their corresponding fault descriptions for these older Mercedes-Benz systems. By counting the blinks, you can reference this list to understand the potential issue your vehicle is reporting.
| Blink Code | Description |
|---|---|
| 1 | No Malfunctions |
| 2 | Full load contact, throttle valve switch implausible |
| 3 | Coolant temp. read by CIS-E implausible |
| 4 | Potentiometer voltage implausible |
| 5 | O2-sensor signal implausible |
| 7 | TNA-signal (RPM-signal) read by CIS-E implausible |
| 8 | Altitude pressure signal from EZL control unit implausible |
| 9 | Current to EHA is implausible |
| 10 | Idle contact, throttle valve switch implausible |
| 11 | Air Injection System |
| 12 | Absolute pressure values from EZL is implausible |
| 13 | Intake air temp. reading is implausible |
| 14 | Speed signal read by CIS-E is implausible |
| 16 | EGR |
| 17 | O2-sensor line shorted positive to ground |
| 18 | Current to idle speed air valve is implausible |
| 22 | O2-sensor heating current implausible |
| 23 | Short circuit to positive in purge switchover valve circuit |
| 25 | Short circuit to positive in start valve circuit |
| 26 | Short circuit to positive in shift point delay circuit |
| 27 | Data exchange between CIS-E unit & EZL unit interrupted |
| 28 | Intermittent contact in coolant temp. sensor circuit |
| 29 | Difference in coolant temp. read between CIS-E unit & EZL unit |
| 31 | Intermittent contact in intake air temp. sensor |
| 34 | Coolant temp. from EZL unit is implausible |
While this blink code method serves as a rudimentary “Code Reader For Mercedes Benz” for older models, modern Mercedes-Benz vehicles and workshops utilize advanced OBD-II code readers for more in-depth diagnostics and a wider range of fault codes. For newer vehicles, an OBD-II scanner is essential for effective troubleshooting and maintenance.
