Reading Diagnostic Trouble Codes

Data Link Connector:

READING DIAGNOSTIC CODES

1. Connect diagnostic check harness (MB991529). Ground the self diagnosis output pin #1 of the diagnostic connector.

2. Set the ignition switch to "ON".

3. Note the pattern of flashes displayed on the "Check Engine/Malfunction Indicator Lamp". If the Lamp lights but dosen't flash, the ECU has failed.
4. Refer to the diagnostic codes chart to determine which device is causing the malfunction code.

5. Test and repair the offending components as necessary.

6. Clear the malfunction codes by disconnecting the vehicle battery negative terminal for ten seconds or longer.

7. Road test the vehicle and recheck for newly stored diagnostic codes.

8. After the cause of a failure code has been detected and corrected the diagnostic code memory of the ECU should be cleared by disconnecting the vehicle battery for 10 seconds or more.

DIAGNOSTIC CODE INTERPRETATION

The Engine Control Unit (ECU) monitors operation of the emission control system. Some components are monitored continuously, others only during specified operating conditions. When the ECU detects a malfunction lasting longer than a specified period of time the ECU will generate an error code that can be detected at the diagnostic connector.


There are sixteen diagnostic items (including normal operation) that will generate diagnostic codes. The malfunction codes are erased when the vehicle battery is disconnected for more than ten seconds.
NOTE: If the oxygen sensor is disconnected during engine operation for testing purposes a code will be stored and must be cleared after the test is complete.
To test for oxygen sensor codes drive the vehicle a significant distance and check for diagnostic codes before turning the ignition off. Do not however disconnect the battery with the ignition on or the engine running as permanent damage to the vehicle electronic components may result.
If multiple malfunctions occur the diagnostic codes will be sent sequentially beginning with the lowest number code in ascending order with a 2 second pause between each code.
The Check engine lamp will flash for a particular duration and a certain number of times.
FOR EXAMPLE:
Code 13
The lamp will flash one time for approximately 0.5 second. This will represent one unit of ten. There will be approximately a one second delay and then the lamp will flash three times for approximately 0.2 seconds with 0.1 second delay between. This will represent three units of one.
Code 23
The lamp will flash two times for approximately 0.5 second with approximately 0.3 second delay between. This will represent two units of ten. There will be approximately a one second delay and then the lamp will flash three times for approximately 0.2 seconds with 0.1 second delay between. This will represent three units of one.