SIMOS motor management system

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Simos is the name for a series of engine control units from the Volkswagen Group . Compared to the previous Digifant system , Simos aims to further improve the mixture preparation in order to achieve the lowest possible emissions and economical consumption with optimal performance. It has been continuously developed, with additional functions being added or changed depending on the engine type and year of manufacture.


The Simos is an electronically controlled injection system with programmed maps for injection time and ignition point. It has overrun fuel cut-off, lambda control, cold start, warm-up, full load enrichment and activated carbon filter control. The injection valves are activated sequentially and inject the fuel into the intake manifold in front of the intake valves or directly into the combustion chamber. The ignition point is determined electronically in all Simos variants. All Simos variants have cylinder-selective knock detection with one or two knock sensors and electronic idling control with the help of the throttle valve unit. The throttle valve unit contains idle switch and throttle valve potentiometer as well as a servomotor. The air mass is determined with the help of an air mass meter. All Simos variants are adaptive so that the CO value and the idling speed no longer have to be set.

The engine control units have a fault memory and are fully diagnosable. The throttle valve unit and some actuators can be tested by means of an actuator diagnosis.

If individual sensors fail, standard values ​​are assumed. The throttle valve unit has emergency running functions. In most cases, a trip to the workshop is still possible.

Mixture correction

Start detection

The control unit recognizes via terminal 50 that the engine should be started. At this point the starter has not yet engaged and the battery voltage is high enough to ensure that the fuel pump relay switches. The same signal is used to recognize the positions "N" and "P" in an automatic transmission and thus to better stabilize the idling speed. In some vehicle types, the fuel pump is activated for one second when the driver's door is opened in order to be able to build up sufficient pressure in the system. Since the TDC of the first cylinder can only be recognized after two crankshaft revolutions, the injectors inject simultaneously with the first crankshaft revolution after the engine has started. After two revolutions of the crankshaft, the system switches to sequential injection. This ensures a faster engine start.

Cold start

The injection valves are opened longer by the control unit in order to enrich the mixture. The opening time decreases as the cooling water temperature rises. The lambda control is deactivated. The idle air volume is increased by the throttle valve unit. At ambient temperatures below 10 ° C, multiple ignitions are triggered to ensure better cold start behavior of the engine.

Warm-up phase

During the warm-up phase, idling is stabilized by the throttle valve unit. The lambda control is activated when the operating temperature of the probe is reached.

Load changes

The load changes are recognized by the air mass meter. Load shocks are absorbed by the throttle valve unit (soft stop mechanism). In addition, jerking is reduced by changing the ignition angle.

Change in intake air temperature

Detection via a temperature-dependent resistance in the intake tract. The control unit responds by lengthening or shortening the injection time.

Speed ​​limitation

The control unit receives the speed information from the speed sensor for the engine speed and reduces the injection time at a speed that depends on the engine type.

Fuel cut-off

Detection via speed and the idle switch in the throttle valve control unit. The control unit stops the injection when the gear is engaged and the accelerator pedal is released above 1500 rpm.

Full load

Detection via speed and throttle valve position; the control unit also increases the opening time of the injection valves.

Lambda control

A lambda probe detects a rich or lean mixture, and the injection time is changed accordingly.

Ignition timing

The engine control unit adapts the ignition timing with the aid of the cooling water temperature, engine speed, load status and the knock sensor (s). The idling is also stabilized via the ignition point.


All Simos variants largely use the same actuators and sensors for the basic function and are marked with version numbers depending on the engine code and type. Older versions have various signal inputs and outputs for engine speed, speed and consumption information, idling speed increase, automatic transmission and immobilizers. The throttle valve unit and the accelerator pedal are connected here by an accelerator cable. Newer versions use the CAN bus and have an electronic accelerator pedal, an electronically controlled cooling system and a dormant ignition system. The newer exhaust gas limit values ​​added an exhaust gas recirculation valve and, in later versions, a linear pre-cat lambda probe and a post-cat lambda probe. For direct injection petrol engines with demand-controlled fuel systems and engines with variable intake manifold, electrohydraulic engine mountings or camshaft adjusters, there are variants with corresponding actuators, sensors and characteristic maps stored in the control unit. The Simos was installed in many Volkswagen Group models from 1994 to 2011.

Overview of the Simos variants

version model Displacement design type Cyl. kW / PS MKB construction time
Simos 1 1.6 l 1,595 line 4th 74/100 AFT 7/1995 - 10/2000
Simos 1 1.6 l 1,595 line 4th 74/100 AKS 4/1997 - 10/2002
Simos 1 2.0 l 1,984 line 4th 85/115 ADY 7/1994 - 2/2000
Simos 1 2.0 l 1,984 line 4th 85/115 AGG 7/1995 - 12/2001
Simos 1 2.0 l 1,984 line 4th 85/115 AKR 4/1997 - 4/2000
Simos 2 1.6 l 1,595 line 4th 74/100 AEH 9/1996 - 10/2005
Simos 2 1.6 l 1,595 line 4th 74/100 AKL 8/1997 - 5/2007
Simos 2 1.6 l 1,595 line 4th 74/100 AHL 10/1996 - 8/2000
Simos 2 1.6 l 1,595 line 4th 75/102 AVU 5/2000 - 4/2002
Simos 2 1.6 l 1,595 line 4th 75/102 BFQ 5/2002 - 12/2010
Simos 2P 1.0 l 997 line 4th 37/50 AHT 10/1998 - 5/2000
Simos 3PE 1.2 l 1,198 line 3 47/64 AZQ 11/2001 - 12/2004
Simos 3PD 1.2 l 1,198 line 3 40/54 AWY 7/2001 - 5/2004
Simos 3 1.6 l 1,598 line 4th 92/125 AVY 10/2000 - 3/2002
Simos 3.2 2.0 l 1,984 line 4th 85/115 AZM 10/2000 - 3/2008
Simos 3.2 2.0 l 1,984 line 4th 85/115 ASU 1/2000 - 8/2000
Simos 3.2 2.0 l 1,984 line 4th 85/115 AUZ 1/2000 - 8/2000
Simos 3.3 1.6 l 1,595 line 4th 74/100 AWH 11/1999 - 10/2000
Simos 3.3 1.6 l 1,595 line 4th 74/100 AYD 6/2000
Simos 3.3 1.6 l 1,595 line 4th 74/100 APF 3/2000 - 4/2001
Simos 3.3 1.6 l 1,595 line 4th 75/102 BFS 6/2002
Simos 3.3 1.6 l 1,595 line 4th 85/115 BLF 2/2004 - 10/2008
Simos 3.4 1.6 l 1,595 line 4th 74/100 ANA 8/1998 - 8/2000
Simos 3.5 2.5 l 2,461 line 5 85/115 APL 5/1999 - 12/1999
Simos 3.5 2.5 l 2,461 line 5 85/115 AVT 12/1999 - 6/2003
Simos 4 1.6 l 1,595 line 4th 75/102 ALZ 6/2000 - 9/2010
Simos 5S 2.5 l 2,461 line 5 85/115 AET 8/1996 - 9/2003
Simos 6 3.2 l 3.123 V6 6th 188/255 AUK 4/2004 - 3/2009
Simos 6 2.4 l 2,393 V6 6th 130/177 BDW 4/2004
Simos 7.1 1.6 l 1,595 line 4th 75/102 BGU 5/2003 - 7/2007
Simos 7.1 1.6 l 1,595 line 4th 75/102 BSF 5/2005 - 11/2010
Simos 7.2 1.6 l 1,595 line 4th 75/102 BSE 5/2005 - 5/2011
Simos PPD 1 2.0 l 1,968 line 4th 103/140 BKP 3/2005 - 5/2009
Simos 8 2.8 l 2,773 V6 6th 154/210 BDX 11/2006 - 7/2010
Simos 8 3.0 l 2,995 V6 6th 245/333 CAKA from 3/2009
Simos 10.2 1.2 l 1,197 line 4th 77/105 CBZB from 8/2009


  • Korp, Dieter: now I'm helping myself - VW Passat from model year 2005 1st edition, Motorbuch Verlag, Stuttgart, 2008, ISBN 3-613-02690-2