Simos 33a Pinout Top ((new)) May 2026

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.

6. Safety Warnings & Best Practices

Never apply reverse polarity – The Simos 33A has no external protection diode on battery inputs. Reversing A1–A3 will instantly fry the main power management IC.
Use a current-limited bench supply – Set to 2A initially when probing new pins.
Do not pull the connector while powered – The 154-pin connector is not designed for hot-plugging. Arc damage on pins A1–A3 is common.
Ground yourself – The CPU inside is static-sensitive. Top-side pins near the center (rows C/D) route directly to the MPC56xx microcontroller.

Step 1: Locate Power and Ground (KL30 & KL31)

Look for thick copper traces leading to the connector pins. These are always power or ground.
Use a multimeter in continuity mode. Touch one probe to a large ground plane (the exposed copper on the edge of the PCB). Probe the connector pins on the top side – the pin that beeps is KL31 (Ground).
KL30 (Battery+) will have a trace leading directly to a large electrolytic capacitor (usually 4700µF or similar). Find the capacitor's positive leg; trace it back to the connector pin.

5. Differences Between Simos Variants (33A vs 32A vs 34A)

The Simos 33A pinout top differs from its siblings:

| ECU | Connector Type | Top Row | Ignition Driver | Common In | |------|----------------|---------|----------------|------------| | Simos 32A | 121-pin | 3 rows | External | Fiat Grande Punto 1.2 | | Simos 33A | 154-pin | 4 rows | External IGBT | Fiat 500, Alfa Mito 1.4 | | Simos 34A | 180-pin | 4 rows (wider) | Integrated | Suzuki Swift 1.6 |

If you mistakenly use a 32A pinout on a 33A, you will likely ground critical outputs (e.g., swapping A8 with A4). Always verify the label on the ECU case: “Continental Simos 33A.6”. simos 33a pinout top

Step 3: Identify KL15 (Ignition Wake-Up)

KL15 is not a high-current pin. It usually connects to a voltage divider (two resistors in series) that then feeds a microcontroller pin.
On the top view, look for a small 10k-100k ohm resistor near the main connector. One side will be connected to a pin (KL15), the other to the MCU. Probe for 12V only when ignition is ON.

4. Connector/Circuit Grouping (Top Connector)

For repair or pinout tracing, group logically:

A. Power & Ground

Pins 1 (+30), 3 (+15), 2 (GND)

B. Ignition System

Pins 16, 17 (ignition coils – waste spark)

C. Fuel System

Pins 11, 12, 23, 24 (injectors)
Pin 13 (fuel pump relay)

D. Sensors – Engine Management

Pins 6 (TPS), 20 (coolant temp), 7 (IAT GND), 8 & 9 (RPM), 10 (knock), 32 (cam), 29 & 30 (MAP)
Pin 19 (lambda), 31 (lambda heater), 18 (lambda GND)

E. Idle Control

Pins 25–28 (stepper motor IAC)

F. Emissions Control

Pin 14 (EGR), Pin 15 (secondary air)

Practical Notes for "Pinout Top" Usage:

"Top" means you are looking at the component side of the ECU's printed circuit board, or the wire harness connector face with the locking clip oriented correctly (usually at the top or side).
Probing: When back-probing the connector from the wire side, the pin numbers are reversed left-to-right. Always verify with a multimeter before piercing wires.
Variants: Some SIMOS 33A ECUs have different pin assignments for idle control (some use a 3-wire rotary idle valve instead of 2-wire stepper). Check your specific hardware number (e.g., 0261204638, 06A906018E).
Common failures: Pins 20, 21, 22, 23 (power and ground) are known for corrosion. Pins 29/30 (crank sensor) cause no-start if signal is weak.

Part 3: How to Identify Key Pins on the Top Side Without a Diagram

Sometimes you don't have a pinout table. Using the top view of the PCB, you can identify critical connections with basic tools.

SIMOS 33A (60-Pin) Top View Pinout

| Pin | Function | Typical Wire Color | Notes | |-----|----------|--------------------|-------| | 1 | Injector Cyl 1 | Brown/Yellow | | | 2 | Injector Cyl 2 | Brown/Blue | | | 3 | Injector Cyl 3 | Brown/White | | | 4 | Injector Cyl 4 | Brown/Red | | | 5 | Injector Cyl 5 | Brown/Green | (If 5-cyl) | | 6 | Injector Cyl 6 | Brown/Grey | (If 6-cyl) | | 7 | Fuel Pump Relay | Blue/Yellow | | | 8 | Main Relay (87) | Blue/Red | | | 9 | GND (Sensor Ground) | Brown/Black | | | 10 | GND (Power Ground) | Brown | | | 11 | GND (Power Ground) | Brown | | | 12 | GND (Power Ground) | Brown | | | 13 | +12V Battery (Permanent) | Red/Black | | | 14 | +12V Ignition (15) | Black/Yellow | | | 15 | +12V (Main Relay feed) | Red/White | | | 16 | Lambda Heater Ground | Brown | | | 17 | Lambda Signal (Bank 1) | Black/Grey | | | 18 | Lambda Signal (Bank 2) | Black/White | | | 19 | Throttle Position Sensor (TPS) Signal | Blue/Green | | | 20 | Intake Air Temp (IAT) Signal | Brown/White | | | 21 | Coolant Temp (CTS) Signal | Brown/Red | | | 22 | Knock Sensor 1 Signal | Shielded | | | 23 | Knock Sensor 2 Signal | Shielded | | | 24 | Cam Position Sensor (Hall) Signal | Green/White | | | 25 | Crankshaft Position Signal (CKP) | Black/Blue | | | 26 | Ignition Output Cyl 1 | Green/Black | | | 27 | Ignition Output Cyl 2 | Green/Yellow | | | 28 | Ignition Output Cyl 3 | Green/Red | | | 29 | Ignition Output Cyl 4 | Green/Brown | | | 30 | Ignition Output Cyl 5 | Green/Blue | (If 5-cyl) | | 31 | Ignition Output Cyl 6 | Green/Grey | (If 6-cyl) | | 32 | Idle Air Control (IAC) – Close | Blue/Black | | | 33 | Idle Air Control (IAC) – Open | Blue/Yellow | | | 34 | EVAP Purge Valve | White/Green | | | 35 | VVT Solenoid (Intake) | White/Red | (If equipped) | | 36 | VVT Solenoid (Exhaust) | White/Black | (If equipped) | | 37 | A/C Compressor Relay | Grey/White | | | 38 | Cooling Fan Relay (Low) | Grey/Black | | | 39 | Cooling Fan Relay (High) | Grey/Red | | | 40 | Check Engine Light (MIL) | Grey/Blue | | | 41 | Diagnostic K-Line (ISO 9141) | White/Yellow | | | 42 | Diagnostic L-Line (ISO 9141) | White/Red | (Rare) | | 43 | CAN High (if CAN-equipped) | Orange/Black | | | 44 | CAN Low (if CAN-equipped) | Orange/Brown | | | 45 | Speed Signal Output | Purple/Black | | | 46 | Brake Switch Signal | Red/Yellow | | | 47 | Clutch Switch Signal | White/Black | | | 48 | Power Steering Pressure Switch | Blue/White | | | 49 | A/C Request Signal | Grey/Green | | | 50 | +5V Sensor Supply | Red/Green | | | 51 | +5V Sensor Supply | Red/White | | | 52 | GND (Sensor Return) | Brown/White | | | 53 | GND (Sensor Return) | Brown/Red | | | 54 | MAF Signal | Green/White | | | 55 | MAP Signal (if used) | Blue/White | | | 56 | Not used | – | | | 57 | Not used | – | | | 58 | Not used | – | | | 59 | Not used | – | | | 60 | Not used | – | | This ECU is commonly found in late 1990s