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This page will cover the Alfa 75 Fuel Quality Plug (S30) on cars fitted with Bosch Motronic ML4.1 EFI
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Fuel Quality Plug (S30) Bosch Motronic ML4.1

Bosch Motronic ML4.1 equipped cars have a fuel quality plug which is referred to as S30 on Alfa wiring diagrams.

On the Alfa 75, this plug is a red relay base which is found near the ECU on the firewall in front of the front passengers feet.
Selection of fuel quality is via one of three different coloured plugs or no plug.

Inside these plugs are simple wire links, these are described below.

Light Blue Plug.

91 octane (ron) or greater vehicle is fitted with a catalytic converter ECU runs in "closed loop" mode pins 85, 86 and 87 are connected

Yellow Plug.

95 octane (ron) or greater vehicle is fitted with a catalytic converter ECU runs in "closed loop" mode pins 85 and 87 are connected

Red Plug.

95 octane (ron) or greater vehicle is NOT fitted with a catalytic converter ECU runs in "open loop" mode pins 86 and 87 are connected

No Plug.

97 octane (ron) or greater vehicle is NOT fitted with a catalytic converter ECU runs in "open loop" mode no pins are connected

This is my yellow "plug"

NOTE! The ECU running in open or closed loop is based on my observations and may be wrong.
              Octane values come from Alfa documentation.






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