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If you are working on a modern Volkswagen Group (VAG) vehicle—specifically models like the Mk7 Golf, Audi A3 8V, or various SEAT and Skoda models from roughly 2012 to 2017—you have likely encountered the SIMOS 33A Engine Control Unit (ECU).
Produced by Continental, the SIMOS 33A is a complex, high-performance ECU designed to manage direct injection and turbocharging efficiency. Whether you are a mechanic chasing a no-start condition or a tuner bench-flashing for performance, understanding the SIMOS 33A pinout is essential.
Disclaimer: This guide is for educational purposes. Always verify pinouts with the specific wiring diagram for your vehicle’s model year and VIN before applying power or jumpers. Incorrect connections can permanently damage the ECU.
For exact pinout matching your vehicle:
Would you like a simplified schematic showing power, ground, sensors, and actuators grouped separately for troubleshooting?
Assuming you mean the Siemens SIMOS 33A engine control unit (ECU) connector pinout — common in some Volkswagen/Audi/Seat/Skoda vehicles — here’s a compact reference for the connector "Top" (often the 55-pin / 67-pin SIMOS variants vary; this follows the common 55-pin SIMOS 33A layout). Use this only as a guide — verify against vehicle-specific documentation before wiring.
Connector: SIMOS 33A — Top row (pin numbering left-to-right when viewing the ECU mating face with locking tab up). Pins are shown as: Pin number — Signal / Typical function — Notes
1 — GND (chassis ground) — ECU ground
2 — CAN High (CAN H) — Powertrain CAN bus high
3 — CAN Low (CAN L) — Powertrain CAN bus low
4 — Battery + (B+) — Permanent battery supply (fused)
5 — Ignition 15 (IGN) — Switched ignition supply
6 — 5V reference — Sensor supply reference
7 — MAP / Boost sensor input — Manifold absolute pressure
8 — IAT / Air temp sensor input — Intake air temperature
9 — CLT / Coolant temp sensor input — Engine coolant temperature
10 — Crankshaft position (CKP) — Primary crank sensor input
11 — Camshaft position (CMP) — Cam sensor input
12 — Knock sensor 1 — Knock input (engine bank-dependent)
13 — Knock sensor 2 — Secondary knock input (if fitted)
14 — Fuel injector 1 driver — Low-side injector driver (cylinder 1)
15 — Fuel injector 2 driver — Low-side injector driver (cylinder 2)
16 — Fuel injector 3 driver — Low-side injector driver (cylinder 3)
17 — Fuel injector 4 driver — Low-side injector driver (cylinder 4)
18 — Fuel pump control (FP relay driver) — Fuel pump relay control (switched output)
19 — Ignition coil driver 1 — Coil driver (or coil pack control)
20 — Ignition coil driver 2 — Coil driver
21 — Ignition coil driver 3 — Coil driver
22 — Ignition coil driver 4 — Coil driver
23 — TPS / Throttle position sensor — Throttle potentiometer input
24 — EGR valve control / N75 — EGR or turbo bypass control (model dependent)
25 — Idle control valve (IAC) — Idle air control / stepper or PWM
26 — Lambda sensor (oxygen) heater control — O2 sensor heater output
27 — Lambda sensor signal (upstream) — O2 sensor voltage input (bank 1)
28 — Secondary lambda / downstream signal — (if fitted)
29 — CAN GND / Chassis reference for CAN — optional/variant
30 — Vehicle speed / VSS — Speedometer/ABS speed signal input
31 — Brake switch input — Brake pedal / cruise inhibit
32 — Clutch switch input — Clutch pedal / cruise inhibit
33 — Neutral / Park switch — Gear selection input (if applicable)
34 — A/C request input — Air conditioning compressor request
35 — Fan control output 1 — Radiator fan relay control
36 — Fan control output 2 — Radiator fan stage 2
37 — Evaporative purge valve control — EVAP canister purge
38 — Ambient air temp input — Ambient temp sensor (if used)
39 — Accelerator pedal position sensor 1 — APS sensor 1
40 — Accelerator pedal position sensor 2 — APS sensor 2 (redundant)
41 — Start inhibit / starter motor input — Cranking detection input
42 — Immobilizer / PATS input — Immobilizer transponder data line
43 — Serial data / K-line (diagnostic) — Older K-line diagnostic port
44 — LIN bus / secondary serial — Variant-dependent
45 — CAN 2 High / FlexRay (variant) — Secondary bus high (if present)
46 — CAN 2 Low / FlexRay (variant) — Secondary bus low (if present)
47 — Alternator sense / L-terminal — Charge warning / alternator field sense
48 — Fuel rail pressure sensor — Fuel pressure sensor input (if fitted)
49 — Turbocharger control (VNT / boost) — Boost control solenoid driver
50 — Secondary injector drivers / spare outputs — Variant-dependent
51 — Knock ground / sensor ground — Dedicated sensor ground
52 — Switched supply for sensors (IGN2) — Secondary switched supply
53 — Ground (battery negative) — Main ground return
54 — Reserved / manufacturer test pin — DO NOT CONNECT
55 — Reserved / manufacturer test pin — DO NOT CONNECT
Notes:
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Siemens Simos 3.3A (often labeled Simos 33A) is an engine control unit (ECU) primarily used in Volkswagen and Audi vehicles, such as the Audi A3 1.6L (engine codes AEH, AKL). ECU Overview and Key Features Application : Management system for 4-cylinder petrol engines. Connector Type : 80-pin multi-plug connector. Service Tasks : Common procedures include reading pin codes for (immobilizer bypass) or cloning using bench tools like the Simos 3.3A Pinout Summary
Based on the standard 80-pin wiring diagram for the Simos 3.3A (1.6L engine), the following are the primary power, ground, and communication pins: Pin Number(s) Ground (Main) Positive (+) Battery (Terminal 30) Ignition Switch (Terminal 15) K-Line (Diagnostics) Fuel Pump Relay Control Engine Speed Sensor (G28) Injector and Sensor Wiring Simos series Current Flow Diagram
details the following specific connections for the fuel system: : Controlled via pins that trigger based on firing order. Hall Sender (G40) : Typically connected to pin 62. Coolant Temperature Sender (G62) : Provides input for engine management adjustments. Bench Connection Guide
For "top" or bench-mode access (for flashing/reading), professional tools often use the following standard setup: Power (+12V) : Pin 18 (Permanent) and Pin 3/37 (Switched). Ground (-) : Pins 1 and 2. Communication simos 33a pinout top
: K-Line at Pin 43 is the primary method for Simos 3.3A/3.4A ECUs.
Simos Control Unit Wiring Diagram | PDF | Fuel Injection - Scribd
Simos 3.3a is a variant of the Siemens Simos engine control unit (ECU) commonly found in Volkswagen Group vehicles, such as the VW Jetta and Golf. Pinout diagrams for these ECUs are essential for bench flashing, diagnostic testing, or repair. General Pin Identification for Simos 3.3/3.3a When viewing the ECU connector from the
(the side where the harness plugs in), pins are generally numbered in a specific sequence to prevent incorrect wiring. Pin 1 Location
: Typically identified by a small dot or a molded "1" near one of the corners of the connector housing. Reading Sequence
: Numbers usually proceed sequentially along a row before moving to the next. Key Identification Points Main Power (+12V) : Often found on specific pins like Terminal 30 for constant power and Terminal 15 for ignition-switched power. Ground (GND) : Common ground connections are often labeled as Terminal 31 Communication
: 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
For common VAG Simos ECUs, standard connections often follow this general pattern: Power (+12V)
: Pins 2, 16, or 121 (depending on the specific 80-pin or 121-pin configuration). : Pins 5, 9, or 121. : Pin 110 or Pin 48 in many Siemens Simos layouts. Recommended Resources for Diagrams
Because pinouts can vary slightly based on the specific engine code (e.g., AEH or AKL), it is critical to verify the schematic for your exact vehicle. Detailed technical guides can be found on: Ross-Tech Wiki for VAG-specific diagnostic and wiring information. Scribd ECU Manuals for specific current flow diagrams. Do you need the specific pin numbers for a bench power-up, or are you looking for sensor-specific wiring locations?
Current Flow Diagram for Simos Control | PDF | Fuel Injection - Scribd
The Simos 3.3A is an engine control unit (ECU) commonly used in Volkswagen Group vehicles, such as the Audi A3 1.6L, to manage fuel injection and ignition systems. Understanding the "top" pinout is essential for bench-reading, remapping, or diagnosing electrical faults. Simos 3.3A Pinout Overview
For bench connections, the Simos 3.3A generally requires connections to power, ground, and a communication line (K-Line). Note that pin numbers may vary slightly by specific engine code (e.g., AEH or AKL), but standard bench-reading pins typically include: +12V Power (Permanent): Pin 3 +12V Switched (Ignition): Pin 1 Ground (GND): Pin 2 K-Line (Communication): Pin 43 The Ultimate Guide to the SIMOS 33A Pinout:
For more detailed technical specifications and wiring diagrams, you can consult the SIMOS Injection Guide or the SIMOS 3.4 ALZ System Overview for related architecture. Key Components & Functions
The Simos 3.3A manages several critical engine functions. A complete "top" pinout map typically features connections for:
Injectors: Controlling the pulse width for fuel delivery to each cylinder.
Ignition Transformer: Managing the spark timing via a dedicated final stage.
Sensors: Monitoring the Hall Sender (G40), Engine Speed Sender (G28), and Knock Sensors (G61/G66).
Throttle Control: Operating the throttle valve actuator (V60) and potentiometers (G69/G88). Bench Reading and Diagnostics
Professionals often use specialized tools like the New Trasdata or Simos Tools to unlock and flash these units. For bench testing, ensure a stabilized power supply is used to avoid corrupting the EEPROM data.
If you are replacing a faulty unit, remember that these ECUs often require immobilizer adaptation or "immo-off" procedures. Tools such as Poldiag are frequently used by automotive locksmiths for these security resets.
The Simos 3.3A (often paired with Simos 3.4A) is an engine control unit (ECU) primarily found in VAG group vehicles like the and VW Golf with 1.6L engines.
For bench testing, reading, or flashing this ECU, the "top" pinout typically refers to the main 80-pin connector (T80). Simos 3.3A Key Pin Connections
Based on standard VAG Simos 3 series wiring, the essential pins for power and communication are generally as follows: Main Power (+12V): Pin 1: Main battery positive (Terminal 30). Pin 3: Ignition switched positive (Terminal 15). Ground (GND): Pin 2: Main chassis ground (Terminal 31). Communication:
Pin 43: K-Line (Diagnostic interface for tools like VAG 1551 or VAS 5051).
Pin 19 / 21: Often used for CAN-High and CAN-Low in later CAN-bus variants, though early 3.3A units rely heavily on the K-Line. Connector Layout The Simos 3.3A uses a large 80-pin connector. ErWin (VAG official portal) – Paid, but accurate
T80 Connector: The pins are usually numbered from left to right, often in rows (e.g., 1-20, 21-40, etc.).
Internal Access: For some advanced boot-mode reading, soldering pads may be located in the middle of the board, though this is more common for Simos 6.x and higher series. Visual Reference Guides
You can find detailed wiring diagrams and full 80-pin maps on technical document platforms like: Simos 3 Motor Management Overview (via Scribd). Simos 1.6L Wiring Diagram (via Scribd).
Are you trying to perform a specific task with this ECU?I can provide more targeted details if you Troubleshooting a no-start or sensor signal issue? Performing an engine swap (e.g., 1.4L to 1.8T)? Current Flow Diagram for Simos Control | PDF - Scribd
Combines fuel injection, ignition timing, and electronic throttle control (EPC). Communication:
interface for diagnostics via tools like VAG 1551 or VAS 5051. Components:
Interfaces with the G28 Engine Speed Sender, Hall Sender (G40), and multiple Coolant Temperature Senders (G2, G62).
For a detailed visual of the "top" view or specific PCB soldering pads, technicians often refer to Simos ECU Connection Guides on Scribd Skoda Fabia Simos 3 Pinout Guide troubleshoot a specific sensor issue?
Simos 7.1 Pinout and Installation Guide | PDF | Fuel Injection
The SIMOS 33A topology is also used in:
Always compare your ECU part number (e.g., 06A 906 018 GR, 037 906 025 G) against a vehicle-specific wiring diagram.
When you remove the lid of a Simos 33A ECU, the top side reveals the following key landmarks: