GLA 220d, GLA 250 and GLC 220d Across the Generations

The X156 GLA 220d is where the GLA story starts for most New Zealand buyers. Underneath that compact, almost hot hatch ish body sits the OM651 DE 22 LA, a 2143 cc four cylinder turbodiesel with an 88.0 x 88.3 mm bore and stroke, a 16.2:1 compression ratio, and a factory output of 177 hp and 350 Nm. It is a genuine performer for a crossover of this size, and for years it proved itself as a sharp daily driver that handles Auckland traffic and motorway runs equally well.

The OM651 is a proven unit, but proven does not mean bulletproof. It has specific weak points that tend to appear as the kilometres stack up, and most of them are made worse by a diet of short city trips.

The transmission is worth a special mention. The 7G DCT in these cars is not a Mercedes in house unit, and it does not respond well to neglected fluid. Jerky low speed shifts and hesitation on pull away are often the first sign something is brewing. Catch it early with a proper fluid and filter service and you can usually avoid bigger bills. Leave it and the mechatronic unit tends to get involved, which is a different conversation entirely.

On the emissions side, the DPF and EGR circuit need attention. We clean and service these systems properly using genuine parts. Cars that have spent years on short suburban runs often arrive with a DPF that is well past its regeneration limit and an EGR valve caked in carbon. That combination almost always triggers limp mode, and it is entirely preventable with the right service interval.

The H247 generation GLA arrived with a substantially updated look and a brand new engine under the bonnet. The M260 is a 1991 cc direct injection turbocharged petrol unit with an 83.0 x 92.0 mm bore and stroke, a 10.5:1 compression ratio, and a factory output of 224 hp and 350 Nm. It pairs with an 8G DCT dual clutch gearbox, this time an in house Mercedes unit, and the whole package feels noticeably more refined than the X156 it replaced.

Where the older GLA 220d's character came from its diesel torque, the GLA 250 feels keener and more eager to rev. The cabin is quieter, the infotainment is a generation ahead, and the suspension tuning is more settled. If you are shopping between these two, the GLA 250 is the more comfortable daily. The GLA 220d is the better long distance motorway runner on economy.

The intake valve carbon issue is the one that catches GLA 250 owners off guard. Because the M260 uses direct injection only, fuel never washes the backs of the intake valves, and carbon from blow by gases accumulates steadily. You will not necessarily feel it in the first 60,000 km, but beyond that point rough idle, slight hesitation and reduced top end pull are the usual signs. The fix is a proper intake clean, not a bottle of fuel additive.

Compared to the X156's 7G DCT, the 8G DCT in the H247 is generally more refined, but it still benefits from correct fluid and filter service to avoid the jerky low speed shifts that owners sometimes mistake for a transmission fault. Get the fluid done at the right interval and it is rarely a problem.

The X254 GLC 220d is a different beast from either GLA. It is bigger, more premium, and considerably more sophisticated under the skin. The OM654 2.0-litre four cylinder diesel replaces the old OM651, and it brings with it a 48V mild hybrid starter generator, a modern automatic gearbox, and a full emissions suite that includes a DPF, an EGR circuit, and a complete AdBlue SCR setup. The factory output is 197 hp. The drive quality is excellent when everything is working. The complexity means there is more that can go wrong, and the consequences of deferred servicing are more significant than on either of the older GLAs.

The OM654 is a better engine than the OM651 in almost every measurable way. It is quieter, cleaner, and more efficient. But it carries all of the diesel emission hardware that the OM651 had, plus the added layer of the 48V mild hybrid components. That means the fault landscape is broader.

The AdBlue SCR system on the X254 is more involved than anything on the older GLAs. When it triggers a fault, the car will count down to a no start condition if the issue is not addressed. We diagnose and repair these systems properly, from NOx sensor faults through to SCR catalyst and injector issues. We do not work around emissions systems; we fix them correctly so the car runs as it should and passes WOF requirements.

Compared to the GLA 220d's old OM651, the OM654 in the GLC is a chain driven engine as well, so the same advice applies: listen for cold start rattle and verify tensioner health if the service history is incomplete. The 48V system adds a layer of complexity that the two GLA generations simply do not have, so the right diagnostic tooling is not optional here, it is essential.