[Repair Case] 2019 Audi A3 cruise control function fails

Model: 2019 Audi A3.

Fault phenomenon: The cruise control function fails.

Troubleshooting: 

(1) Read the trouble code with the ODIS diagnostic instrument: 01—engine control unit record—U041600—ESP untrusted signal (active/static).

(2) According to the test plan, it is necessary to compare the configuration of the SVM control units for 01-engine control unit J623 and 03-ABS control unit J104. After the online SVM comparison, it is prompted that the two control units are configured correctly and do not need to be changed.

(3) At this time, the ODIS diagnostic instrument has been unable to provide the test plan for maintenance and can only perform diagnostic testing based on experience and maintenance data. Query SSP-612/9-16 to learn that the J104-ABS control unit equipped on the A3 car integrates the G202 yaw rate sensor, the G200 lateral acceleration sensor, and the G251 longitudinal acceleration sensor in the J104-ABS control unit, so it is no longer necessary. Instead, the separate G419 sensor unit appears as a whole within the J104-ABS control unit software.

(4) Since the fault could not be recorded in 0.3—ABS control unit, the focus of inspection was placed in J623—engine control unit. According to the ELSA pro circuit diagram, check the power supply fuse of J623—engine control unit step by step, and there is no abnormality in grounding.

(5) Step by step check the power supply fuse of the J104-ABS control unit according to the ELSA pro circuit diagram, and there is no abnormality in the grounding.

(6) Check the circuit between J236-engine control unit and J104-ABS control unit according to ELSA pro circuit diagram, but no abnormality is found.

(7) Since all inspections failed to find the cause of the fault at this time, try to replace the J623-engine control unit and compare it with the online SVM, and rewrite all the matching value data of the car. Currently, the J623-engine control unit stores the recorded data. Trouble code: U041600: The ESP unreliable signal has changed to passive/occasional and can be cleared. During the test drive, it was found that the cruise control function returned to normal. However, the cruise function is lost again after driving about 3 miles.

(8) Since the failure of replacing the J623-engine control unit could not be resolved, try to replace the J104-ABS control unit, and test the vehicle again. After driving approximately 30 miles the fault could not be reproduced, so it is judged that the fault has been eliminated.

Analysis of the cause of the failure: J104—the internal data of the ABS control unit is damaged.

Troubleshooting method: Replace J104-ABS control unit.

Special tools/equipment: VAS6150D, VAS1526E.