Bosch ME7.1 on the longitudinal 1.8T

Bosch Motronic ME7.1 (petrol, torque-based / drehmomentgeführt) — VAG 1.8T 20v LONGITUDINAL only: Audi A4 B5/B6 & A6 C5, VW Passat B5/B5.5 (the Passat B5 shares the Audi longitudinal platform). K03/K03s stock, K04 upgrade. NOTE: the TRANSVERSE 1.8T (Golf/GTI, TT, A3, Beetle — the 180/190/210/225 hp cars) uses ME7.5, which is a close sibling but out of scope here.

Reference - updated 4 August 2026

The ECU hardware

Bosch ME7.1. MCU: Siemens/Infineon C167-series 16-bit (C166 core), typically a C167CR/C167CS mask — confirm the exact derivative per box code. Data is little-endian (LSB-first / Intel / LoHi). External NOR flash holds BOTH program code and the full calibration Datenstand: 512 KB AMD/Fujitsu/ST 29F400 is standard for the 1.8T ME7.1. (The 1 MB 29F800 belongs to the 2.7T ME7.1 sibling — do NOT assume 1 MB on a 1.8T.) A SEPARATE 95040 SPI serial EEPROM (512 bytes) holds the immobilizer + adaptation/learned values — NOT the tune. Flashed over K-line on these longitudinal cars.

Fuelling and load sensing

Petrol/gasoline. 95 RON (91 AKI) minimum for an aggressive map, 98 RON (93 AKI) preferred; ignition de-rated on lower grade. Open-loop WOT target lambda ~0.80-0.85 (rich for knock + EGT protection); part-throttle closed-loop stoich (λ=1). Port injection — no high-pressure DI fuel rail.

How this ECU is read and flashed

Read/written over OBD-II K-line, ISO 14230 KWP2000 (K-line ONLY on these longitudinal 1.8T cars — no CAN flash). A free open-source OBD flasher reads full flash in ~5 min and writes in ~3.5 min, with full + partial (calibration) R/W and verify. Requires KWP2000 SECURITY ACCESS (the ME7 seed/key algorithm is public). IMMOBILIZER: if the tool reports 'immobilizer not authenticated' the flash is blocked — the ECU must be authenticated in-car (paired cluster + valid key) or the immo deleted first. Immo/adaptation live in the SEPARATE 95040 serial EEPROM and are NOT disturbed by a program-flash tune (reflashing program flash does not touch immo). BENCH/BOOT recovery (for a failed/interrupted OBD write / bricked ECU): the C167 bootstrap loader (BSL) over K-line, entered by grounding the C167 bootstrap pin, or BDM/direct programming of the 29F400 flash chip. Always ME7Sum + ME7Check the file before every write.

Engine codes in this family

• AEB
• ATW
• AWT
• AMB
• APU
• ANB
• BEA
• AVJ

Staging - what each stage really gives

• stage1 - Software only, stock K03/K03s turbo + stock injectors/MAF. Raise LDRXN (peak boost ~0.6-0.7 -> ~0.9-1.0 bar), raise KFMIRL load request, tune KFLDRL/KFLDIMX WGDC pre-control, optimize KFZW/KFZW2 timing, set LAMFA ~0.82-0.85, keep KFMIOP/mimax and the torque ceiling consistent so the level-2 monitor does not cut. Typical: the 150 hp longitudinal cars (AEB/ATW/APU/ANB) -> ~180-190 hp; the 163/170 hp cars (AMB/AVJ) -> ~200-215 hp; roughly +30-45 hp and +40-60 lb-ft. Requires 95-98 RON. No hardware. (Note: the 180/190/210/225 hp figures belong to the TRANSVERSE ME7.5 1.8T, not these ME7.1 cars.)
• stage2 - Bolt-ons: turbo-back/downpipe (hi-flow cat or decat), front-mount intercooler, cold-air intake, uprated diverter valve. Reduced backpressure + better charge cooling let the K03 hold higher boost (~1.0-1.1 bar) more sustainably. Re-tune boost/timing/fuel around the hardware; rescale MLHFM if the MAF housing changes. Typical ~200-225 crank hp. Stock injectors reach their duty-cycle limit (~85%) at the top — watch for lean-out.
• stage3 - Turbo upgrade: K04 (or hybrid/big-turbo GT28/GTX-class). Requires larger injectors (K04 ~380cc; big turbo 440-630cc) -> rescale KRKTE + regenerate TVUB, and if the matching K04 fueling maps are available copy them for a clean scale; larger MAF housing -> rescale MLHFM; uprated in-tank fuel pump; FMIC; upgraded clutch/flywheel for the torque; sometimes cams/head/valvetrain work. Boost ~1.2-1.5 bar. K04 ~240-260 hp; big turbo ~280-350+ hp. Stock connecting rods become the limiting factor — forged rods recommended past ~280-300 whp.

Safety limits

• WOT lambda 0.80-0.85 (~11.8-12.5 AFR); NEVER leaner than ~0.88 under boost — lean-under-boost = knock, holed pistons, burnt exhaust valves
• Pre-turbo EGT < ~950 C sustained — protects the K03/K04 turbine wheel and exhaust valves; LAMFA + component-protection (Bauteilschutz) enrichment is the primary EGT lever
• Knock retard: keep minimal — sustained ignition retard beyond ~6 deg means pull timing/boost or raise octane; log per-cylinder retard with ME7Logger and watch IAT (heat-soaked small K03 pulls timing on rising intake temp)
• Boost: K03/K03s ~1.0-1.1 bar (15-16 psi) max efficient; K04 ~1.2-1.4 bar — beyond that = compressor overspeed/surge and excess heat; taper LDRXN toward redline
• OVERBOOST FUEL CUT: ME7 hard-cuts fuel if measured load/boost exceeds LDRXN by more than the calibrated threshold + debounce — a SEPARATE protection from the torque monitor. A spiky/overshooting boost curve trips it; smooth the target and tune KFLDRL/KFLDIMX so actual tracks requested
• MAF SATURATION: the stock HFM5 MAF + housing peg near ~4.9-5.0 V / their max airmass around stock-turbo flow; once the MAF clips, load and fueling metering are LOST (runs open-loop wrong/lean). Bigger turbo/airflow REQUIRES a larger MAF housing + correctly rescaled MLHFM
• Injector duty cycle < ~85% — if pegged you go lean at the top; upgrade injectors and rescale KRKTE/TVUB rather than run them maxed. Also verify in-tank fuel pump capacity keeps rail pressure up at high flow (port injection: no HP DI rail, so no rail-pressure map — fuel supply limit is pump + injector DC)
• N75/WGDC: do not hold ~95%+ duty at redline (turbo overspeed); taper LDRXN/duty toward the limiter
• Stock connecting rods reliable to ~250-280 whp / ~300+ lb-ft — big-turbo torque beyond this risks rod failure; go forged
• Clutch/gearbox: the stock clutch and the 01A/012 manual (and especially the 01V tiptronic auto, which has its OWN torque limiter) slip/fail past roughly stock-torque + margin — upgrade clutch/flywheel for Stage 3 torque; do not raise the tune past what the driveline can hold
• Fuel octane: 95 RON (91 AKI) minimum for aggressive maps, 98 RON preferred — de-rate timing on lower grade
• Catalyst/emissions: no DPF on this petrol engine (diesel-only); a decat throws P0420 and removes cat over-temp margin — keep EGT/enrichment in check if the cat is retained
• Always re-run ME7Sum + ME7Check and confirm map dtype/endianness AND geometry on-file (sane values at both axis extremes) before flashing — a bad checksum bricks/no-flashes, a mis-decoded map mis-fuels the car

Every car using this platform (2)

Stock power and typical remap figures per car. Stage results assume a healthy engine on good fuel.

How confident is this?

HIGH (corroborated live against s4wiki and TracQi ME7Tuner/MxT docs): the torque-based architecture; the function labels and their roles (KFMIRL inverse model, LDRXN max-charge boost cap, KFMIOP/mimax forward model, KFLDRL feed-forward WGDC precontrol, KFLDIMX integrator limit, KFZW/KFZW2, LAMFA, KRKTE, TVUB, MLHFM, KFKHFM); KFVPDKSD/E being a THROTTLE pressure-ratio coordination map; the multi-region additive checksum + ME7Sum corrector / ME7Check validator; OBD K-line KWP2000 flashing and the 'immobilizer not authenticated' behavior; the injector scaling method (KRKTE = 34.125/cc-min plus the 0.000111 factor caveat and TVUB regeneration); and the AFR/EGT/octane/overboost-cut safety envelope. All 8 engine codes are valid 1.8T 20v. MEDIUM: exact flash size per box code (512 KB / 29F400 is standard for the 1.8T; 1 MB / 29F800 is the 2.7T sibling, not typical here); exact MCU mask (C167CR vs CS); per-map dimensions/dtype (vary by software version); which maps carry inline vs shared axes; whether a given box code is cam-equipped (KFZW2 relevance) — early AEB/ATW are not, later AMB/AVJ are. Anything less certain than that is called out in the text and must be verified per car before you write to an ECU.