This is a standard reference for the 60-pin connector used in many VAG (Volkswagen Audi Group) vehicles from the late 1990s to early 2000s (e.g., VW Golf MK4, Bora, Audi A3 8L, Seat Leon, Skoda Octavia 1U) with 1.6L, 1.8L, and 2.0L engines.
The SIMOS 33A is a robust ECU, but its small form factor and densely packed pins require careful attention to detail. Whether you are diagnosing a sensor fault or setting up a bench harness, having the correct pinout map saves hours of frustration.
Are you looking for a specific pin number not listed here? Let us know your vehicle model in the comments below!
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
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 simos 33a pinout top
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
: 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
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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Understanding the pinout for the Siemens Simos 3.3A ECU—commonly found in Volkswagen models like the Beetle, Golf, and Polo—is essential for bench programming, diagnostics, or IMMO off procedures. Simos 3.3A ECU Bench Pinout
For "bench" mode (connecting directly to the ECU pins without the car), you typically need to establish power, ground, and communication. According to standard technical guides for tools like MPPS V18 and PCMtuner, the pin assignments are: +12V (Power): Pins 1, 3, and 62 GND (Ground): Pin 2 K-Line (Communication): Pin 43
Note: Some variations may use Pin 43 specifically for the K-Line diagnostic signal required for reading the EEPROM or flash memory on the bench. Professional Bench Tools
Several tools are frequently used to interface with this ECU for cloning or reading pincodes:
DC706: Often used for IMMO off and pincode reading directly on the bench.
BitBox: Supports Simos modules for K-Line reading and writing. This is a standard reference for the 60-pin
PCMflash: Commonly uses Module 1 or specialized boot protocols for Simos units. Important Service Tips
Stable Power: When performing "Bench" or "Boot" operations, always use a stabilized 12V-14V power supply. Low voltage during a write process can "brick" the ECU.
IMMO Off: Many technicians seek this pinout specifically to perform an IMMO off, which is a common fix for older VW vehicles with failing immobilizer systems.
Visual Verification: Always refer to a physical diagram or the markings on the ECU connector to ensure you are counting the pins from the correct side (top-down vs. front-facing).
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
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. Troubleshooting Tips
This ECU is commonly found in late 1990s to early 2000s Volkswagen Group vehicles (Volkswagen, Audi, Seat, Skoda) with 1.4L, 1.6L, and 1.8L naturally aspirated (non-turbo) engines, such as the Polo, Golf Mk4, Lupo, Fabia, Ibiza, and A2.
Many online guides confuse the top (component side) and bottom (solder side) pinouts.
| Feature | Top View (This Article) | Bottom View | | :--- | :--- | :--- | | Perspective | Looking at the ECU with lid off, connectors facing you. | Looking at the PCB solder joints. | | Pin Numbers | Follow silkscreen or physical plastic numbering. | Often reversed (mirror image). | | Use Case | Probing with multimeter, bench flashing, identifying test points. | Soldering wires for bypass, ECU repair (reflowing joints). | | Danger Level | Low if careful. Exposed circuits can short. | High – you can bridge pins easily. |
Golden Rule: When working with the top view, always ensure no metal tools touch two adjacent pins. The Simos 33A operates at 5V logic levels; a short between 5V_REF (Pin 31) and Sensor GND (Pin 30) will instantly destroy the 5V regulator.
This pinout is provided for reference and diagnostic purposes only. Do not probe or apply voltage to unknown pins without a factory wiring diagram for your specific vehicle. Incorrect wiring can destroy the ECU.
If you need the bottom (solder side) pinout or a harness-side (female connector) pinout, let me know.
The Siemens Simos 3.3A is an Engine Control Unit (ECU) commonly found in VAG group vehicles (Volkswagen, Audi, Seat, Skoda) from the early-to-mid 2000s, such as the Audi A3 1.6L (AVU engine). Simos 3.3A Pinout for Bench Operations
To perform operations like reading the pincode or "Immo Off" on a bench, you must connect to specific pins on the ECU's main connector. The following pinout is commonly used by professional tools like the OBDSTAR DC706: +12V (Power): Pins 3, 23, and 62 GND (Ground): Pins 1 and 2 K-Line (Communication): Pin 17 Technical Capabilities
Engine Management: The Simos 3.3 system manages fuel injection, ignition, and electronic throttle actuation (EPC) in a single unit.
Memory Components: It typically contains a 29F400BB Flash chip and a 93C76 EEPROM.
Bench Reading: Tools such as the OBDSTAR DC706 or PCMtuner can read and write both the Flash and EEPROM data in bench mode to clone the ECU or bypass immobilizers. User Experience and Tips
OBD Limitations: While some Simos versions support OBD reading, users often report that Simos 3.3 may not work via OBD for full read/write operations, necessitating a full system pinout on the bench.
Resources: For detailed visual diagrams, automotive professionals frequently use databases like ImmoOFF or Cairo Car Tuning which provide high-resolution PDF pinout maps.
Are you planning to perform a clone or an immobilizer delete on this specific ECU?