Audi A5 & S5: B8 2.0 TDI, B8 S5 3.0 TFSI and Mk3 3.0 TDI

The first generation A5 8T with the CAHA 2.0 TDI common rail diesel is a genuinely good car. One thousand nine hundred and sixty eight cubic centimetres, 170 horsepower, 350 Nm, and that long low roofline that still gets second looks. It sold well in New Zealand and there are plenty of them still doing solid daily kilometres. Which means plenty of them are now at the age where the well documented weak points start showing up.

The EGR valve and cooler are the first thing to watch. Auckland stop start traffic is exactly the kind of use pattern that accelerates carbon build up, and once the EGR starts clogging, rough idle and loss of power follow. Closely related is the intake manifold with its swirl flaps: they carbon up too, and when a flap breaks free it can travel somewhere you really don't want it to go. We see both regularly.

The DPF is another recurring story. If this A5 has spent most of its life on short suburban runs, it may never have completed a proper regeneration cycle, and a blocked DPF is an expensive fix compared with a clean and reset done early. The turbo actuator can also start playing up on higher mileage cars, showing up as flat spots or over boost faults. And the dual mass flywheel, well, it's not a question of if, it's a question of when.

One thing that matters a lot on this platform: the CAHA is cambelt driven, not chain driven. Miss that belt interval and the consequences are immediate and catastrophic. We replace the cambelt and water pump together, using new genuine parts, and we log it properly so there's no ambiguity next time around.

Compared with the later Mk3 3.0 TDI, the 2.0 CAHA is simpler and cheaper to work on. There's no AdBlue system to worry about, the rear of engine timing chain isn't a factor, and parts availability is good. It's the entry point to the A5 family and, properly maintained, it's a very satisfying one.

The B8 S5 with the CAKA 3.0 TFSI sits at the emotional peak of this generation. Three litres, a Roots type supercharger bolted into the V of the engine, 333 horsepower and 440 Nm delivered without any turbo lag whatsoever. It is a brilliant driving experience. It is also a complex piece of German engineering that has a few well known weaknesses once the kilometres stack up.

The supercharger snout bearing is the one to know about. It wears over time and when it goes, the noise it makes is hard to ignore. A worn snout bearing doesn't fix itself. Getting it sorted before it turns into a supercharger replacement job is the sensible move, and we fit new genuine parts when we do it. The water pump is another common wear item on this engine, and given how much trouble a cooling system failure causes on any performance engine, it makes sense to replace it proactively when you're already in there.

Carbon build up on the intake valves is a reality for any direct injection engine, and the CAKA is no exception. Because fuel is injected directly into the cylinder rather than past the intake valves, there's nothing washing the back of those valves clean. Over time, carbon accumulates and starts affecting flow and combustion. It's not a crisis, but it's something that should be addressed before it gets heavy.

Compared with the 2.0 TDI in the same B8 generation, the S5 is more expensive to service and the labour on some jobs is significantly more involved. But the driving experience is in a different league, and a well maintained CAKA engine is genuinely long lived. The S5 is also the most popular car in this family for Stage 1 tuning, and for good reason.

The Mk3 A5 with the DCPB 3.0 TDI V6 under the bonnet is what happens when Audi decides that a diesel coupe should genuinely embarrass sports cars. Two hundred and eighty six horsepower and 620 Nm of torque from a diesel V6. It's extraordinary. It's also a more complex car than either of its predecessors, and the extra capability comes with a few things worth knowing before you buy or before you start ignoring service intervals.

The timing chain on the DCPB lives at the rear of the engine. That's the first thing to understand, because accessing it is a major job. A cold start rattle that goes away once the engine warms up is not something to file away as 'probably fine.' It's the chain and tensioner telling you something, and catching it early is the difference between a chain service and an engine out job. We take it seriously.

The AdBlue and SCR system is new to this generation and it's where many owners get caught out. NOx sensor faults, incorrect dosing, low AdBlue warnings that weren't topped up on time: these can stack up and leave the car in limp mode. The system needs factory level tooling to diagnose and reset properly, not a generic reader. We carry out AdBlue top up, NOx sensor replacement and SCR system diagnosis as part of our routine work on this car.

The EGR cooler and intake carbon story is familiar from the 2.0 TDI generation, but on a V6 the labour to access and service those components is higher. That makes preventative cleaning worthwhile rather than waiting for a fault code to force the issue. The DPF can also load up on short trip cars, and the Mk3 A5 deserves the occasional open road run to complete a full regeneration cycle.

Against the 2.0 TDI, this car is noticeably more complex and more expensive to service. Against the S5, it trades the theatre of the supercharger for sheer torque and diesel efficiency. For someone who covers serious kilometres and wants genuine performance without petrol costs, the DCPB is a compelling proposition.