* A 1-pole switch has 3 connections (1 x in, 2 x out). In switch position "1", the input signal is applied to the first output, with switch position "2" to the second output. A 2-pole switch has 6 connections (2 x 3) and can thus switch two signals.

This article describes how the serial sequential turbocharger control (first starts Turbo # 1, then Turbo # 2) can be electrically set to parallel operation (Turbo # 1 and Turbo # 2 running in parallel) and back again.

How it works : The functions of the exhaust control valve and the intake air control valve are set to either "Sequential mode" or "Parallel mode" via a two-pole changeover switch. The respective mode can be changed while driving.

System Control in Detail: Normally, the exhaust and intake air control solenoid valves are activated by the engine control unit (ECU), which turns on the second turbo from about 4,500 RPM to the charging system. In this modification (E-TTC), the minus lines of the solenoid valves are connected through a switch either to loop through to the ECU or to ground. This makes it possible to switch back and forth between standard control and parallel operation.

ATTENTION! This conversion requires that pipes and valves,
ATTENTION! especially the accumulator, work properly.
ATTENTION! Always disconnect the ground cable from the battery before working on the ECU.

Necessary hardware: 2-pole switch * (available eg from www.conrad.de )

Installation: The switch is looped into the lines between the exhaust control valve (VSV2) and ECU, and between the intake air control valve (VSV1) and the ECU. The ECU (bottom left) is located under the carpet in the passenger footwell.

Position of the signal lines on the ECU connector:


Legend: IACV = intake air control valve, EGCV = exhaust control valve Diagram of the standard wiring:
Legend: Intake air control valve (VSV1 = green-blue cable), exhaust control valve (VSV2 = green-yellow cable)

To install the switch, disconnect the two cables from the VSVs to the ECU, and connect the cable ends leading to the VSVs to the switch inputs. The cables leading to the ECU are connected to the two first outputs of the changeover switch, the other outputs of the changeover switch are grounded.

Diagram of wiring after conversion:

Connections at the counter:

Notes on the application:

Switching from sequential to parallel:
At idle, it is possible to switch from SEQ (sequential loader control) to TTC (parallel loader control) at any time. As soon as the first loader has built up some pressure, this pressure is directed via the pressure accumulator to the control boxes and opens the valves. This is the 2nd Turbo permanently switched on.
In the middle speed range should not be switched to TTC mode, since this could kickstarted the 2nd Turbo, if the exhaust bypass valve is closed at this time. Only from 4.500 RPM can safely be switched back to TTC, since both turbos then already run in parallel anyway.

Switching from parallel to sequential:
Both at idle and while driving can be switched back from any time from TTC to SEQ, as long as no positive boost pressure is present. To switch to SEQ must therefore be only briefly gone from the gas.

Translation from the English by Don