Simos 33a Pinout Top May 2026

One of the most common points of confusion is the connector orientation. The SIMOS 33A typically utilizes a multi-plug system with three distinct rows or connector blocks plugged into the ECU casing.

When looking at the ECU installed in the car (usually in the plenum chamber near the windshield), the connectors are often stacked. In wiring diagrams and repair manuals, these are often referred to by their position or color:

Note: In many SIMOS 33A diagrams, the connector containing the power and communication lines (the logic side) is physically positioned on the outer edge (or "top" when viewed from a specific angle), separate from the heavy-current coil/injector pins.

Below is the Simos 33A pinout top view for the main 154-pin connector. This table lists pins visible from the top side when the connector is unmated from the ECU and facing upward.

| Pin | Signal Name | Function | Typical Color (OEM) | |------|----------------|------------------------------------|------------------------| | A1 | BATT+ | Main battery voltage (30) | Red / Red-Blue | | A2 | BATT+ | Main battery voltage (30) | Red / Red-Blue | | A3 | BATT+ | Main battery voltage (30) | Red | | A4 | GND | Power ground | Brown / Black | | A5 | GND | Power ground | Brown | | A6 | GND | Power ground | Brown | | A7 | 15_IGN | Ignition switched power (15) | Green-Black | | A8 | 87_WU | Relay output (main relay) | Red-Yellow | | B1 | INJ_1 | Injector cylinder 1 | Yellow | | B2 | INJ_2 | Injector cylinder 2 | White | | B3 | INJ_3 | Injector cylinder 3 | Blue | | B4 | INJ_4 | Injector cylinder 4 (if 4-cyl) | Violet | | B5 | IG_A | Ignition coil A (cyl 1 & 4) | Green | | B6 | IG_B | Ignition coil B (cyl 2 & 3) | Green-Yellow | | C1 | O2_11 | Lambda sensor 1, bank 1 (pre-cat) | Black / Gray | | C2 | O2_12 | Lambda heater ground | White / Brown | | C3 | O2_21 | Lambda sensor 2, bank 1 (post-cat) | Gray | | C4 | TPS_5V | Throttle position sensor 5V ref | Orange | | C5 | TPS1_SIG | TPS signal (main) | Orange-Black | | C6 | TPS2_SIG | TPS signal (redundant) | Orange-Red | | D1 | CAN_H | CAN bus (high) | Orange / Yellow | | D2 | CAN_L | CAN bus (low) | Orange / Brown | | D3 | K_LINE | K-line diagnostic (ISO 9141) | Purple | | D4 | CKP_SIG | Crankshaft position sensor signal | Shielded pair (Blue/White) | | D5 | CMP_SIG | Camshaft position sensor signal | Shielded pair (Green/White) | | D6 | ECT_SIG | Engine coolant temperature sensor signal | Brown-Red |

📌 Note: This table shows the most common assignments for a 4-cylinder Simos 33A. V6 or diesel variants may have different pinouts. Always check your specific OEM documentation.

This is the most critical plug for bench testing. This is where the high-current power is delivered.

Tip for Bench Technicians: When bench wiring a SIMOS 33A, you must supply +12V to Pin 1 and Pin 6, with grounds on Pins 2 and 3, to establish communication with a flashing tool.

Mastering the Simos 33A pinout top is essential for anyone working on modern Fiat, Alfa Romeo, Suzuki, or GM small-displacement turbo engines. The 154-pin top layout groups battery and ground on the left (pins A1–A8), injectors and ignition on the right (B1–B6), and sensors/diagnostics along the middle rows (C/D). simos 33a pinout top

Before probing or flashing, memorize the critical pins: Battery = A1–A3, Ignition = A7, Ground = A4–A6, CAN = D1/D2. With this guide and a multimeter, you can confidently bench-test, repair, or retune this powerful yet delicate ECU.

Have a specific Simos 33A pinout question? Leave a comment or contact our support team for vehicle-specific diagrams.

The Siemens Simos 3.3A (06A 906 033 A) is a legacy engine control unit (ECU) found primarily in the Audi A3 8L and Volkswagen Golf Mk4 with the 1.6L 8V (102HP) petrol engine. Its pinout configuration is essential for technicians performing bench-top diagnostics, IMMO-off procedures, or EEPROM/Flash reading. Technical Overview

The Simos 3.3A belongs to the Simos 3 family, which is known for its relatively straightforward hardware but sensitivity to specific communication protocols when accessed via bench tools. Primary Application: Audi A3 I (8L), VW Golf IV 1.6i.

Key Components: Typically utilizes a 29F400 Flash chip and a 93C76 or similar EEPROM for data storage.

Engine Management: Capable of processing up to two knock sensor signals via piezo-resistive senders. Bench Pinout Configuration (Standard)

For bench-top reading and writing (using tools like PCMflash or MPPS), the following "Top" view pin connections are standard for the 80-pin or 121-pin connectors (check your specific hardware revision): Pin Number (Common 121-pin) +12V (Main Power) Permanent power supply to the ECU. +12V (Switched/Ignition) Ignition signal (Terminal 15). Ground (GND) Main chassis ground connection. K-Line (Data) Diagnostic communication channel. CAN High/Low Pins 19/20 (if equipped) High-speed bus communication. Performance and Reliability Review Pros:

Simplicity: Highly documented in tuning communities like ECU Connections, making it easy to troubleshoot or modify. One of the most common points of confusion

Durability: The hardware is robust and rarely suffers from internal component failure compared to newer, more complex units. Cons:

Reading Limitations: Some older variants may require "Boot Mode" (grounding a specific pin on the PCB) to write to the Flash memory.

Tool Compatibility: Modern tools like the KT200II can occasionally experience freezing or "not responding" errors when communicating with older Simos units in bench mode. Expert Tip

When working with the Simos 3.3A on the bench, ensure you use a stable 13.5V to 14V power supply. Voltage drops during the "Write" phase can corrupt the Flash memory, often requiring a desoldering of the chip to recover the unit using an external programmer. Simos 8.3/8.4 boot read ECU connection issue - Facebook

The pinout for the Siemens Simos 3.3a ECU , commonly found in VAG (Volkswagen, Audi, Seat, Skoda) vehicles with 1.6L engines (like the AVU or BFQ codes), is essential for bench reading, pincode retrieval, and IMMO-OFF procedures. Core Bench Pinout (Power & Communication) For standard "on-the-bench" operations using tools like OBDSTAR DC706 , the primary connections are made to the 81-pin main connector Pin Number(s) Description +12V (Permanent) Main power supply +12V (Ignition) Switched power Ground (GND) Main chassis ground Diagnostic communication line Component-Specific Pinout Data

Beyond basic power, specific pins handle critical engine actuators and sensors: Fuel Injector II: Pin 33A (Signal from vehicle's ECU). Fuel Injector I: Engine Speed Sender (G28):

Inductive sender usually connected to dedicated inputs for crank angle calculation. Camshaft Position (G40): Hall sender used for engine speed calculation if G28 fails. Programming Notes These units typically feature a 29F400BB Flash 93C76 EEPROM Bench Mode: Most modern tools can perform Read Pincode

via K-Line on the bench without opening the case, provided the 12V, GND, and K-Line connections are correct. Boot Mode: Note: In many SIMOS 33A diagrams, the connector

If bench reading fails, some variants require grounding specific pads on the PCB (BSL mode) to enable programming. Always "probe" or verify continuity to the processor pins before applying voltage to unknown pads.

For detailed wiring diagrams including sensor colors and relay locations, the VW ElsaWin software

are the standard professional resources for these older VAG systems. or to resolve an immobilizer issue

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 64-pin ECU. It uses three separate connectors (often labeled A, B, and C). However, the common terminology for identifying "top" refers to the main engine harness connector (usually Connector A or T80) or the physical top row of the 64-pin arrangement.

On most SIMOS 33A ECUs:

Important: Pin numbers, colors, and functions can vary slightly depending on:

This write-up provides the most common top connector pinout (60-pin or 64-pin depending on production year), used in majority of SIMOS 33A ECUs. Always verify with your specific wiring diagram.