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).
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 simos 33a pinout top
Interfaces with the G28 Engine Speed Sender, Hall Sender (G40), and multiple Coolant Temperature Senders (G2, G62). The Ultimate Guide to the SIMOS 33A Pinout:
This is the 60-pin connector layout (viewed from the component side / top side of the PCB, looking into the connector pins). The connector is physically large and rectangular, with
Combines fuel injection, ignition timing, and electronic throttle control (EPC). Communication:
The Simos 33A ECU uses a 154-pin Tyco / AMP connector (often referred to as the "Tyco 154-pin header"). The connector is physically large and rectangular, with pins arranged in several rows. When the ECU is mounted in the car, the connector faces downward. However, when you remove the ECU and flip it over for bench work, the top side refers to the side of the connector where the plastic housing mates with the ECU’s circuit board.