Quote:
Originally Posted by DrFerry
No, the SES doesn't 'cause' the car to go into limp mode.
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I need to be a bit clearer.
The computer (ECU) in your M3 is constantly receiving information, in the form of voltages, from your O2 sensors. Those voltages from your O2 Sensors are compared to pre established voltages programed into your ECU. Those pre-established voltages are fixed and put their by the dealer on orders from the EPA or, in my case, the California Air Resources Board, CARB.
CARB has dictated that voltage levels coming out of your O2 sensors above a certain base voltage can "possibly" lead to "unacceptably high emissions."
Because it is merely a "possibility", only your "Service Engine Soon" (SES) light comes on. With the SES light on, your car keeps running normally; but, you wont pass the California smog test (i.e., the CARB test). Bottom line, under the "possible" scenario, CARB has dictated your only going to drive in a normal way ( in California) up until when your smog test must be passed.
On the other hand, when the voltage levels coming out of your O2 sensors are high enough, CARB has determined you are no longer "possibly" causing unacceptably high emission but you are, in fact, causing unacceptably high emissions. That's when they shut you down. CARB forces your car past the SES condition and into what is called the "limp mode."
Lot's of people think the "limp mode" has been established to prevent some catastrophic engine component (or drive train) failure. Baloney.
The limp mode and the SES light are there to stop you from screwing up the environment. The people pulling the strings would refer to your "limp mode" predicament as a necessary means of imposing "environmental justice."
https://www.epa.gov/environmentaljus...and%20policies.