The Siemens Simos 3.3A is a common engine control unit (ECU) found in VAG group vehicles (Volkswagen, Audi, Skoda, Seat), particularly for the 1.6L petrol engines (engine code BFQ).
E. Idle Control
: K-Line communication for diagnostics is frequently assigned to a single pin (e.g., Pin 37 or similar depending on the specific VAG harness version). EMIT Connect Bench Connection Essentials
B. Ignition System
💡 Aftermarket tuning platforms like PCMFlash, Ktag, and Magicmotorsports often include a .pdf pinout inside their software folder. Look for “SIMOS33A_pinout_top.pdf”.
| Symptom | Likely Cause | Top-Side Test | | :--- | :--- | :--- | | No communication (OBD) | CAN bus short or transceiver dead | Measure resistance between Pin 23 & 24 – should be 60Ω (with bus loads). | | ECU won't wake up | No KL15 signal | Probe Pin 5 (Top view) – 0V key off, 12V key on. | | Random misfires on one cylinder | Injector driver FET shorted | Measure pin to ground (e.g., Pin 48). If <10Ω, FET is dead. | | 5V sensor fault (P0641, P0651) | 5V reference shorted to ground | Unplug sensors; measure Pin 31 & 32 to ground. If still 0V, internal failure. |
Current Flow Diagram for Simos Control | PDF | Fuel Injection - Scribd
Ground (GND): Standard connection to the ECU case or designated ground pins.