Turbos

The turbo has changed face three times in twenty years: diesel VGT, petrol TFSI, then micro-turbos 1.0–1.5

Until the mid-2000s, the European turbodiesel parc revolved around fixed geometries or simple mechanical wastegates, fitted to engines such as the 1.9 TDI (codes AFN, AGR, AHF, ASZ, BJB, BKC…) or the 1.9 dCi / DTI (F9Q, F8Q families). The first major shift came with the widespread adoption of variable-geometry turbos (VGT / VNT) on second-generation common-rail engines: 2.0 TDI 140 and 170 (BKD, BKP, BMN, BMR…), 2.0 HDi 110 (RHS, RHZ), 2.5 TDI (AFB, AKE, AKN…) and also 2.3 dCi / M9T on light commercials. The second shift, on the petrol side, was marked by fixed-geometry turbos with wastegates on the 1.8 T (AEB, ANB, AWM…) and 2.0 TFSI (AXX, BPY, BWA, CAEA, CAEB, CDNB, CYPA…), followed by twin-scroll or bi-volute turbos on the N54, N55 and B48 BMW engines. The third and most recent shift concerns low-inertia micro-turbos fitted to the 1.0 TSI / TCe / T-GDi and the 1.2 THP / PureTech (EB2DT, EB2DTS, HNP, HNS…), where the CHRA and bearings are dimensioned differently from those of 2.0 L engines.

Diesel, petrol, light commercial: three identification approaches

On variable-geometry diesel engines, the same engine capacity can take several different turbos depending on power output and year: a 2.0 TDI 140 (BKD) does not share the same manufacturer reference as a 2.0 TDI 170 (BMN) or a 2.0 TDI 190 (codes CNHA, DDAA…). On larger light commercials — Transit (EcoBlue BCFA…), Master (M9T), Daily (F1A, F1C), Ducato (F1C, F1CE…), Transporter (BJL, CECA…) — the turbo is often supplied as a reconditioned exchange unit, as high mileage and demanding load conditions accelerate wear on the bearings and actuator. On turbocharged petrol engines, the most common cause of failure is insufficient lubrication at start-up or after a hot shutdown: degraded oil, a blocked feed pipe, or switching the engine off without allowing it to cool down. On diesel engines, EGR / DPF fouling and oil laden with soot particles are the primary causes of excessive play on the turbine shaft.

New turbo or reconditioned turbo: what this guide covers

Depending on the reference, the turbo is available either new (straightforward sale, no old unit to return) or reconditioned on an exchange basis. Reconditioned exchange units cover the majority of common references for the most widely represented models: A4, A3, Golf, A6, Série 3, Passat, Transit, Astra, Mégane, C4, Leon, Polo, Octavia… New turbos apply to references for which original replacement parts are available and economically viable. In both cases, identifying and rectifying the root cause of the failure before fitting is essential: a foreign body drawn into the intake, an air leak on the induction circuit, persistent blue smoke, or a limp-home mode must all be diagnosed and corrected — otherwise replacing the turbo will not solve the problem. To find the correct reference, navigate to your make and then your model page, and check the engine code stamped on the block: it is the engine code, not the engine capacity alone, that determines the exact reference.