Audi Q7 & SQ7: 4L, 4M and SQ7 | All Engines, All Generations

The 4L Q7 is the one that set the template: a big, imposing diesel SUV that could genuinely carry seven people while pulling hard enough to surprise most things on the road. The CLZB is a 2967cc V6 diesel producing 245hp and 550Nm, and in the facelift 4L spec it's managed by a Bosch EDC17CP44 ECU. This is a well engineered unit but it has real weak points you need to know about before buying.

The single most discussed item on the CLZB is the timing chain. It lives at the rear of the engine, which means access is the opposite of convenient. Stretch or tensioner wear shows up as a rattle on cold starts, and if you own a 4L Q7 and haven't had that chain inspected, it's overdue. Oil consumption and sludge are also in the conversation on higher mileage examples, and the oil cooler has a known tendency to seep. Turbo actuator faults crop up too, usually presenting as a loss of power or boost irregularity under load.

Beyond the drivetrain, the EGR valve and intake tract carbon up progressively on any diesel used for short urban trips. The DPF needs regular high speed runs or active regens to stay healthy. Where AdBlue is fitted, the SCR system adds another layer of fault potential. The air suspension on this model is genuinely capable but the compressor and struts do wear, and when they go the car drops uncomfortably.

The 4M is a proper step up from the 4L. The car lost significant weight, the interior quality went up a notch, and the 3.0 V6 TDI in 50 TDI tune makes 286hp and 620Nm managed by a Bosch MD1CP004 ECU. Same displacement as the CLZB at 2967cc, but a revised compression ratio of 16.0:1 and meaningfully more power and torque. If you're deciding between the two diesel Q7s, the 4M 50 TDI is the one to have.

The timing chain concern didn't go away with the 4M. It's still at the rear of the engine, still expensive to access, and still something to check carefully on any used example. The oil cooler and thermostat housing have a tendency to seep on these too, which is a familiar story from the 4L. What's new on the 4M is a more involved AdBlue SCR setup. The NOx sensors and SCR catalyst add fault complexity, and the EGR can trigger persistent warning messages if it's carboned up or starting to fail. DPF clogging on short trip driving is exactly the same story as the 4L: the car needs proper regen cycles to stay clean.

Air suspension compressor and strut wear is, if anything, more of a talking point on the 4M because the car is heavier on its feet than it looks and the system works hard. Higher mileage 4M Q7s regularly need compressor attention.

The 55 TFSI is the petrol option in the 4M family and it's a fundamentally different animal. The EA839 3.0T V6 is a turbocharged petrol unit at 2995cc, 340hp and 500Nm, running a dual ECU setup across a Temic AL552 and a Bosch MG1CS002. Many of these cars also carry a 48V mild hybrid system with a belt alternator starter unit, which adds genuine complexity that most workshops aren't set up to diagnose correctly.

Coming from the diesel Q7s, the absence of DPF, EGR soot and AdBlue drama feels like a relief. But the EA839 has its own list. Carbon build up on the intake valves is the most common issue, inherent to direct injection petrol engines because fuel isn't washing the backs of the valves on every stroke. On higher mileage examples this progressively robs throttle response and idle quality. The water pump and coolant thermostat are worth watching too, and the timing chain should be listened to for tensioner noise as the car accumulates mileage.

The 48V mild hybrid system is genuinely clever but adds a layer of fault potential the 50 TDI doesn't have. Belt alternator starter issues, 48V subsystem faults and related warning lights are something we see on these regularly. Reading all of this properly needs ODIS: the dual ECU architecture means a generic tool will often miss half the picture.

Then there's the SQ7. Same 4M platform, same seven seats, same air suspension, but the CZAC is a 3956cc V8 diesel producing 435hp and 900Nm. The torque figure alone sets it apart from everything else in the family. It achieves that number through a triple charging setup: two conventional turbos plus an electrically driven compressor running off the 48V subsystem, which fills the lag gap before the big turbos spool. It's genuinely clever and genuinely complex, and most workshops in Auckland have never seen one properly.

The electric compressor and 48V system are the first thing to understand. Faults here can present as reduced power or warning lights that look unrelated, and reading the 48V control unit correctly requires ODIS. Oil leaks are common on higher mileage CZAC engines, and high pressure fuel system wear is worth checking on any used example. Carbon build up on the intake is the same direct injection story as the 55 TFSI, and the EGR, DPF and AdBlue SCR setup on this engine is as complex as it gets in the Q7 family. The timing chains live at the rear of the block, exactly like the V6 diesel models.