top of page

SQ5 Common Engine Issues by Dan

During the last 3 months of ownership of the 2015 SQ5 with the CGQB engine Bi Turbo V6 diesel. There are clearly maintenance items that either Audi have no idea about in terms of serviceability or they have never had condition-based monitoring on the items which are listed. This list is not the be all and end all, as every person drives their car differently and if you have purchased a used SQ5 there is no telling how the person/people before you drove the vehicle. There are other issues related to the SQ5 but in this case we will stick to the engine reliability conditions, causes and remedies.


With help from Rev High Tuning Solutions in Hallam Victoria, It’s clear that certain items relating to performance and reliability can in some cases leave a lot to be desired. These results listed below are on a case-by-case basis, your SQ5 may have been subjected to different conditions. Conditions relating to long idle times, constant stop start, frequent freeway use all have different consequences relating to reliability.

Daniel's SQ5 TDI 5.png
Daniel's SQ5 TDI 4.png
Daniel's SQ5 TDI 3.png

Top Graph stock run, and first tune, 2 injectors replaced.
Bottom Graph. The remaining 4 injectors were replaced.

First thing first is the diesel injectors. Whether is be premature failure, injector copper sealing washer leaks, or just general wear and tear it is important to understand that although your SQ5 might be running just fine, perceptively it might not be. My SQ5, with approximately 135,000km on the clock failed 2 injectors, this was determined by Audi as these were repaired under statutory warranty. The condition that was noted was a knocking noise coming from the injectors and a sharp pulsing sensation could be felt. After the repairs the vehicle running was improved but not perfect due to running rough on startup. We will touch on this condition and cause as bit later.

Secondly the dreaded injector sealing washer failure, over time due to thermal expansion and contraction these washers which seal between the injector and the head start to fail. The failure allows combustion to leak around the washer. Audi obviously foresaw this as an issue as there is a relief hole in each injector bore which relieves combustion pressure in the event of a washer failure. These holes are important, as combustion can blow by the injector and the eventually destroy the sealing O ring, 1 excessive crankcase pressure can occur and in extreme cases engine run on can occur due to the engine oil being drawn passed the oring and being ingested by that cylinder under certain conditions, where the cylinder in not under a positive pressure IE boost. Injector failure can also occur if the combustion leaks are left too long. A telltale sign you are experiencing leaks is a black carbon glass like substance being ejected from the leak off holes, a smell of combustion inside the cabin and a choofing type noise under the bonnet can in some cases be audible.

Moving on, the other 4 injectors were replaced with new since all the injectors were assumed to have done the same amount of work. This made a significant difference on the dyno with an initial KW and torque increase over the initial tune before the 4 injectors being replaced, and also running leaner which was a lot better for exhaust temps and exhaust/soot emissions. As I’m naughty and I removed my DPF only, with a Darkside developments DPF delete pipe. The ecu needs to be tuned to compensate for the missing DPF.

Carbon build up. This is the thorn in the side any direct injection engine regardless of it being petrol or diesel. In the case of the SQ5, intake valve ports, valves, intake ducts and the intake manifold is basically a breeding ground for this. It’s caused by the EGR system. The soot from the egr coats the inside of the everything intake related with soot, the oily mist from the crank case gas system acts as a binding agent. I won’t go too much into this but a walnut blast is recommended for the intake system, when done properly it will remove the carbon build up from the intake ports and valve. The manifold and intake ducts, swirl flap controller also need a good scrub. Typical conditions of this carbon build up is running rough at idle and cold start misfires. And in some cases, fault codes relating to the function of the swirl flap controller can also occur. After cleaning the full intake system it’s recommended that the EGR be blanked off and the ecu be tuned to compensate for this. Otherwise, you’ll be doing this clean again. Yes the crank case gases don’t help either leaving oily residue inside the intake system, and in some cases catch cans can be fitted, which can bring their own issues. But going by the test results, EGR blanking is sufficient for this not to be an ongoing issue.

Coolant and oil leaks are also a common issue with the V6 diesel, mainly under the intake manifold where you have oil and coolant running very close to each other. The oil cooler seals dry out with the heat that gets trapped under the intake manifold and the cooler seals leak oil and coolant in the V of the engine, the coolant regulator valve which is located close by also eventually

leaks from the shaft seals within the valve, the transition piece between the block and the EGR cooler leaks too and usually breaks off with the EGR when you go to remove it. It’s a really good idea to replace the oil cooler assembly and seals plus all the other before mentioned components when the intake manifold is removed from a carbon clean. Regardless if the components in question are leaking at the time… you will kick yourself if these parts leak in 3 month’s time after having the intake manifold off. Another thing worth replacing while you are in the area is the coolant bypass/bleed off T piece and the series of pipes which connect to the coolant bottle which are prone to failure when being removed due to exposure the from the coolant heat and turbo heat. Water pumps are also susceptible to leaking.

At the end of the day it all comes down to maintenance and cost. It costs $$ to do maintenance, but it also costs $$ when things go wrong due to lack of maintenance. It’s an individual opinion on whether you pay now or pay later.

bottom of page