Audi TT Turbo

TT petrol with fixed geometry, TT diesel with variable geometry: two opposing turbo architectures

The turbo catalogue for the Audi TT is predominantly petrol: six of the eight engine variants fall within the petrol range, from the older 1.8 T units (AGU, AJQ, APP, ARY, ARZ, ATC, AUM, AUQ, AWP, BAM, BFV) through to the modern 2.0 TFSI (CJSA, CJSB, CHHB, CHHC, CNTC, CWZA, CJXA, CJXB, CJXC, CJXE, CJXG, CJXH, CYFB, DJHA, DNUA, DNUC, DNUF). The two diesel variants — 2.0 TDI 170 and 2.0 TDI 184 — use a turbo with variable geometry: the adjustable vanes in the scroll continuously regulate exhaust gas flow, which exposes the actuator and variable-geometry mechanism to fouling and seizure, particularly during low-load urban driving. The TT's petrol engines all use turbos with fixed geometry and a wastegate, which are mechanically simpler, but subject to high thermal stress on the high-output variants (306–310 hp, codes CJXA and derivatives), where housing and bearing temperatures are particularly demanding.

1.8 T and 2.0 TFSI: very different references depending on generation and power output

On the first-generation TT, the 1.8 T 150 and 180 hp variants share several engine codes (AJQ, AUQ, APP) but do not all use the same turbo: the quattro 225 and 240 hp version (BAM, BFV) uses a distinct, larger-dimensioned reference. The move to the 2.0 TFSI introduces a further break: the 220–230 hp versions (CHHB, CHHC, CNTC, CWZA) share no turbo reference with the 306–310 hp versions (CJXA, CJXB, CJXC, CJXE, CJXG, CJXH, CYFB, DJHA, DNUA, DNUC, DNUF), which correspond to the RS designation and use in particular the reference IS38 and its manufacturer equivalents. The 1.8 TFSI 180 hp (CJSA, CJSB) is a standalone engine variant with its own references. Checking the engine code stamped on the block is essential before placing any order: at the same engine capacity, turbos are not interchangeable between different power outputs.

Symptoms and causes to identify before replacement

On the older-generation 1.8 T, the CHRA bearings are sensitive to the quality and regularity of oil changes: degraded oil accelerates rotor wear and causes whistling and blue smoke on acceleration. On the 2.0 TDI (BMN, CBBB, CEGA, CFFA, CFFB, CFGB, CFGC, CFGD, CFJA, CFJB, CLLA, CLLB, DLUB, CUNA), blockage of the turbo oil return circuit and fouling of the variable-geometry mechanism are the most common causes of failure. In every case, the root cause of the failure must be addressed before fitting: a foreign body drawn in through the intake, a blocked oil feed pipe, or an air leak on the inlet manifold will destroy a new turbo just as quickly as the old one. All turbos listed here are new parts, sold with no old unit to return.