Engine self-diagnosis (VW Lt 2d)

The fuel injection system control unit is equipped with a fault memory, which records faults in sensors or systems, indicating the type of fault. Sometimes malfunctions occur that are random in nature (sporadic). Such malfunctions are additionally indicated by the symbol "S/P". If a sporadic fault does not occur after 50 engine starts, it is automatically erased (deleted) from memory. If faults affecting the vehicle's control systems are detected, a warning light comes on. Faults can be read using the VAG 1551 fault code reader or the VAS 5051 tester. Once the fault has been corrected, it must be cleared from the fault memory.

Fault memory is divided into permanent and temporary (the fault is cleared after 50 engine starts).

The selection of functions using the VAG 1551 fault code reader or the VAS 5051 tester is shown in Table 3.7.

Table 3.7. Selecting functions using the VAG 1551 fault code reader or the VAS 5051 tester

Functions		State
Functions of the VAG 1551 fault code reader or VAS 5051 tester		The engine is not running, the ignition is on	The engine is idling	The car is moving
01	Control unit version	Yes	Yes	Yes
02	Querying the fault memory	Yes1)	Yes	Yes
03	Final diagnostics	Yes	Yes	Yes
04	Basic installations	No	Yes	No
05	Clearing the fault memory	Yes	Yes	Yes
06	The final result	Yes	Yes	Yes
07	Control unit code	Yes	No	No
08	Reading a block of measured values	Yes	Yes	Yes
11	Login	Yes	No	No

¹⁾Only when the ignition is on and the engine cannot be started.

Querying the fault memory

To interrogate the fault memory, you need a VAG 1551 fault code reader and a VAG 1551/5 cable.

1. Connect the VAG 1551 (VAG 1552) fault code reader and, by entering "01" "Engine electronics", select the engine control unit. The engine should be idling. In cases where the engine does not start, turn on the ignition. The display should show the following information:

• LT HELP Diagnostics
• Dial function XX

2. Enter "02" to select the "Fault Memory Interrogation" function and confirm by pressing the "Q" button. The display should show the following information:

• Fast data exchange HELP
• Dial function XX

3. Enter "02" to select the "Diesel Engine Management" function and confirm with the "Q" button. The display should show the following information:

X faults detected

If one or more faults are stored

4. The stored faults are displayed and printed one by one. Clear faults from memory after reading them and eliminating the causes of their occurrence.

If there are no faults in the memory

(The original article is available on the website: «VWmanual.ru»)

5. Press "→". The display should show the following information:

• Fast data exchange HELP
• Dial function XX

6. Press "06" to select the "Quick Data Exchange" function and confirm by pressing the "Q" button.

Clearing the fault memory

7. Connect the VAG 1551 (VAG 1552) fault code reader and, by entering "01" "Engine electronics", select the engine control unit. The engine should be idling. The display should show the following information:

• Fast data exchange HELP
• Dial function XX

8. Press "02" to select the "Fault Memory Reset" function and confirm by pressing the "Q" button. If there are one or more faults in the memory, they will be displayed one by one. After displaying the faults loaded into the memory, the following information should appear on the display:

• Fast data exchange HELP
• Dial function XX

9. Enter "05" to select the "Clear Fault Memory" function and confirm by pressing the "Q" button. The display should show the following information:

• Fast data exchange →
• Fault memory cleared

10. If the fault memory has not been cleared, it means that it is in the clearing process. Press "→". The display should show the following information:

• Fast data exchange HELP
• Dial function XX

11. Press "06" to select the "Complete Output" function and confirm by pressing the "Q" button.

12. Perform a test run. Then read the fault memory again, in which nothing should appear.