Bosch ME7.1 on the 2.7T allroad

Bosch Motronic ME7.1 - the Audi 2.7T biturbo (V6 30v, twin K03) in the C5 A6 and allroad. Box codes 4B0907551 (A6) and 4Z7907551 (allroad); the sibling B5 S4 is 8D0907551. 230-250 PS on the A6/allroad and 265 PS on the European S4 (250 hp in the US).

Reference - updated 7 October 2026

The ECU hardware

Two 16-bit Infineon/Siemens C167 CPUs (SAK-C167CR-4RM, marked B59233-FA) — confirmed dual-CPU on ME7.1: a function CPU plus an independent monitoring CPU running the level-2/level-3 torque monitor (question/answer supervision). External program/calibration flash: a single 16-bit AMD/Fujitsu Am29F800BB (44-pin PSOP), 1 MB (8 Mbit) on the 2.7T — code + calibration in one image. Separate serial EEPROM (immo/adaptation, 95040 or 95080). C167 is little-endian (Intel/LoHi); WinOLS 'C167 target' sets this. Flash mapped high. No CAN for flashing on the C5 platform — diagnostics/flash are over K-line (ISO14230 / KWP2000). NOTE: s4wiki states both 512 kB and 1 MB ME7.1 variants exist, so ALWAYS size-check a given dump; the 2.7T/29F800 is 1 MB (independently confirmed on a live 8D0907551 full-flash read in this project).

Fuelling and load sensing

Petrol / gasoline, port (multipoint) injection, 6 injectors, ~95-98 RON recommended (91 RON files exist but pull timing). Full-load enrichment strategy (LAMFA) runs rich under boost for knock/EGT control. Return-style fuel system with a mechanical, manifold-referenced FPR: ~3 bar base rising toward ~4 bar off-vacuum/under boost. No high-pressure DI system.

How this ECU is read and flashed

Read/write is over K-line (ISO14230 / KWP2000, no CAN flashing on the C5). OBD path: Galletto/MPPS/KESS-type tools — KWP2000 security access (seed/key), upload a flash driver to RAM, then erase/program the full 1 MB in blocks. BOOT-MODE / BSL (bench): the C167 bootstrap loader over K-line, immo-IMMUNE, used for recovery + EEPROM writes; requires grounding an internal bootstrap-config pin (documented on the 4Z as a 1K resistor on pin 24 to ground / flash strap to P0L.4) — a cable alone can't do it, the case must be opened. Immo notes: ME7.1 has the immobilizer + separate 95040/95080 EEPROM. On the 4Z the flash-write routine (KWP 10 85) is immo-gated — a MATCHED car flashes over OBD fine, but a mismatched/bench ECU refuses flash and must go boot-mode. EEPROM can be READ over OBD (dev session 10 86 / read services) but WRITTEN only in boot mode; SKC/immo-off writes are refused over OBD. WARNING: the 4Z (esp. 4Z7907551AA) is notoriously fussy — an OBD flash read can set a programming DTC, and some units are hard to force into boot mode. Always have a known-good bin + a recovery path before writing.

Engine codes in this family

• AZA
• APB
• BES
• BEL
• ARE

Staging - what each stage really gives

• stage1 - Software only on stock twin K03, stock injectors, stock intake/exhaust; pump gas (often separate 91 vs 95/98 RON files). Raise LDRXN (+~10-20 load) and KFMIRL to lift peak boost from stock (~10-12 psi peak / ~1.7-1.85 bar abs, tapering) to roughly ~14-17 psi peak (~1.95-2.15 bar abs) WITHIN the K03 surge limit; keep MLHFM/KRKTE stock, trim KFZW for knock, enrich LAMFA slightly. Verify NO torque-monitor intervention. Typical result ~300-320 crank hp and a large mid-range torque bump (~+80-100 lb-ft). Re-checksum with ME7Sum then verify with me7check. (Boost figures are approximate and vary with file/altitude.)
• stage2 - Stage-1 software + bolt-ons: turbo-back / high-flow or test downpipes, upgraded intercoolers (side-mounts or FMIC), high-flow intake, upgraded diverter valves, sometimes a larger MAF housing. Software: MANDATORY MLHFM recalibration for the new intake/MAF (even if boost is similar), modest further LDRXN, timing where knock margin allows, confirm LAMFA. Boost stays inside K03 surge (~15-18 psi peak). Typical ~320-350 crank hp; the added cooling/flow lets the same boost run cooler, safer, and hold longer.
• stage3 - Hardware: K04 hybrids (or larger GT/RS4-style), larger injectors, upgraded fuel pump, larger MAF housing, FMIC, and an upgraded clutch/flywheel (manual) or trans work (tiptronic). Full software rework in LOCKSTEP: KRKTE for the injectors (flow + pressure term), MLHFM for the new MAF, LDRXN up (K04 ~2.0-2.3 bar abs), KFMIRL + KFMIOP peak torque lifted TOGETHER (torque monitor!), LAMFA axis expanded + richer, KFZW pulled for higher cylinder pressure, KFLDRL/KFLDIMX retuned for turbo response. K04 ~380-420 hp. Bigger turbo/built motor ~450-550+ hp, but note STOCK CONNECTING RODS are the mechanical ceiling (commonly considered safe to ~450-500 crank hp and they bend below that under detonation/

Safety limits

• KNOCK is the #1 limit: keep worst-case knock retard (dwkrz / per-cylinder KR) in the SINGLE DIGITS of crank degrees and only transient — sustained multi-degree pull = detonation, holed pistons/ringlands and bent rods.
• Stock connecting rods are the hard mechanical ceiling: they are commonly regarded as safe to about 450-500 crank hp (mid-400s wheel hp), and they bend well below that under detonation, a lean WOT spike, or excessive ignition advance (pre-ignition raises peak cylinder pressure). Anything wanting ~450+ hp reliably, or an aggressive high-boost tune, needs forged rods. It is torque, not just peak hp, that bends them.
• Full-load lambda: run RICH — target ~0.80-0.88 lambda (AFR ~11.8-12.9) at WOT; stock full-load enrichment is ~0.85. NEVER lean past ~0.88-0.90 at WOT for power. Bigger turbo / more timing -> richer (0.80-0.85). A momentary lean-out under boost is a rod/piston killer.
• EGT (pre-turbo): keep below ~950 C on the cast K03 manifolds/turbines; Add fuel + pull timing to drop EGT.
• Boost / K03: peak ~1.5-1.7 bar absolute is the sensible ceiling (K03 compressors surge easily and fall off their efficiency island beyond — more boost just makes heat and shortens turbo life). K04 ~2.0-2.3 bar abs.
• MAP-sensor ceiling: absolute maximum MEASURABLE pressure is 0xffff/25.6 = 2559.96 mBar (~2.56 bar / ~23 psi) with DSLOFS=0, and max SPEC/requested boost is 0xff*10 = 2550 mBar. Exceeding the sensor's range SATURATES/rolls over the pressure signal -> corrupt load & boost calc -> boost cut/limp (it does NOT set P0601 — that code is an internal-memory checksum fault, unrelated). To go higher, use the 5120 hack + a larger MAP sensor and size it for your boost target PLUS the IAT-driven ftbr overhead.
• MAF clipping: keep HFM voltage below its ~5.0 V / MLHFM top-of-scale ceiling — clipping forces open-loop/lean and boost limp. Rescale MLHFM or fit a bigger housing BEFORE adding air.
• Torque monitor (level-2/3): keep mibas < miszul and keep mimax (from KFMIOP) high enough that requested load isn't capped — ALWAYS raise LDRXN + KFMIRL + KFMIOP in lockstep or the independent monitoring CPU cuts timing/fuel mid-pull.
• Boost-deviation faults: keep actual-vs-requested within ~200 mBar — larger sustained deviation trips P1555 (over) / P1557 (under, limp @ ~10% WGDC); watch I-adaptation (ldimxa_0..4) for slow overboost creep near the MAP limit.
• Fuel delivery: the stock in-tank pump + injectors run out of headroom by upper Stage2 / Stage3 — keep injector duty below ~85-90% and upgrade pump + injectors (with KRKTE) before maxing, or fueling goes lean under boost.
• Drivetrain torque: the manual Sachs clutch slips beyond mild torque increases (Stage2+ wants an upgraded clutch); the tiptronic 5HP19 has its own TCU torque limit and overheats/slips on big torque — consider a trans tune / cooler.
• N/A here: no DPF and no high-pressure DI limits — this is a petrol, port-injected engine (those limits belong to diesels / MED17 DI, do not import them).

Every car using this platform (1)

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

How confident is this?

SOLID: ECU identity Corrected to Bosch ME7.1 (the twin-turbo 2.7T is ME7.1 — s4wiki's "7.1.1" is the NA/TT-V6 revision, a different variant; this also matters because ME7Sum fully supports ME7.1 but only 'in testing' for 7.1.1); dual C167CR CPUs (confirmed on s4wiki: 'two 16bit Infineon B59233-FA (aka SAK-C167CR-4RM) CPUs'); Am29F800BB 1 MB on the 2.7T (independently confirmed via a live 8D full-flash read); K-line/KWP2000 flashing; 4Z box-code family; no-crypto additive + multipoint + CRC checksum corrected by ME7Sum then verified by me7check; the map ROLES and the LDRXN<->KFLDHBN<->KFMIRL<->KFMIOP torque-monitor lockstep; MLHFM/KRKTE (flow+pressure)/LAMFA-axis/KFZW functions; boot-mode-via-pin-24 + immo-gated OBD flash on the 4Z; and the fault/limit logic — cross-checked live against s4wiki this session. ADDED the missing STOCK CONNECTING-ROD limit and a fuel-delivery limit, and Corrected the MAP-overflow failure mode (saturation/boost-cut, NOT P0601). MEDIUM: exact flash size for EVERY 4Z sub-suffix (2.7T/29F800 = 1 MB confirmed, but size-check each dump; 512 KB is the 1.8T ME7.5 sibling), per-map dtype/width/endianness (little-endian is the norm but this pipeline hit