Engine Controls - Catalyst Protection Mode Information

SI B12 24 07
Engine Electrical Systems

November 2007
Technical Service

SUBJECT
S54: Catalyst Protection Mode While the Vehicle is Low on Fuel

MODEL
E46 with S54 produced from 09/00 to 08/06

E85 with S54 produced from 03/06

SITUATION
The customer complains that the vehicle has no power during heavy acceleration.

The fuel reserve light is illuminated and the fuel level, when measured with the service tester, is below 10 liters.

The DME fault codes "81 Catalytic-converter protection function as result of empty tank", "95 Fault with empty tank", and various misfire faults, e.g., "C9 Misfiring, cyl. 6 with cylinder cutout." are stored in the DME.

CAUSE
With the fuel level low and under extreme driving conditions (heavy acceleration, cornering or racing), the fuel supply may be inadequate, causing an intermittent lean mixture to be recorded by all 4 oxygen sensors.

Consequently, to avoid catalyst overheating and possible damage, the DME enters protection mode and will reduce the engine speed and torque output.

PROCEDURE

This is a normal vehicle operation and doesn't require any action. Please explain the DME strategy to the customer.

WARRANTY INFORMATION
Information only.





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