AECS Equipment technical support recently assisted in the case of a 2014 Audi Q5 2.0 turbo with boost failure issues.
Problem presented to the Support team
Intermittent engine warning light coming on. Low engine performance while engine light on.
The workshop had run a scan and found some codes for the turbo and coolant temp sensor circuit. A new coolant temp sensor was fitted and this took away the cooling system codes.
The workshop wanted a pathway to locate the turbo issue. The following fault report from the shop's Auscan 4 scan tool was shared.
We suggested monitoring the boost pressure in live data on the scan tool while driving and using the shops two channel ATS500 scope to monitor the turbo actuator motor control wires. These will change polarity as the ECU commands more or less boost, driving the waste gate open/closed.
Fault code P256300 relates to a possible fault in the boost actuator position sensor. P226300 indicates an issue with the boost system control. Therefore it seems logical to monitor the actuator and see if its control motor goes open circuit. This would cause the engine to lose boost but also end up with the actuator position sensor in an illogical position from that being commanded.
After a brief road test the boost pressure dropped out while the switched side of the actuator lost power supply, indicating an actuator motor problem.
A new turbo actuator was ordered and installed. Only to have the engine warning light coming back on for a boost fault code again.
This is where care must be taken. Some turbos come calibrated at the factory and no after market actuator replacement is possible while others calibrate themselves independently. The third type need a special procedure carried out with the aid of a good quality diagnostic tool.
The workshop had measured the length of the actuator control rod with a vernier caliper. This was still not accurate enough.
The following is the learn procedure in the Launch Eurotab 3 scan tool . Note it is a 5 step procedure.
Some engine heat is required. 35 degrees is suggested
The correct adjustment range is a very small 3.4 - 3.6 mm range.
It is interesting to note that even at 3.49mm, we were getting fault codes for boost control. Only on increasing to 3.51 mm did the fault code not get reset. Possibly some wear in the turbo linkages could explain this issue.
It always pays to always check your scan tools special functions. There are an ever increasing number of sensors requiring calibration as new model vehicles enter the market.
