Backup Fuel

[batman1999]

In the factory GM manual (Driveability, Emissions, and Electrical Diagnosis) for my truck it says that when certain DTC (17, 18, 19,...) are set:

"Action Taken (PCM will default to): Backup fuel"

Can someone define Backup fuel for me? Is this something like a "limp home" mode?

Thanks

[DmaxMaverick]

"Back up fuel" is a preset default setting for fuel delivery. Although it can be very conservative, the engine will run, and get you where you need to go. The condition can be accompanied by lowered engine power and limited gears available, which is called "limp mode". Specific codes are set when certain sensors report invalid or predetermined values, or communication is lost. "Back up fuel" is not "limp mode", in itself. It depends on the codes, or combination of codes. An example of "back up fuel" is a loss of the PMD resistor value, if it can't identify it. It will set a code and illuminate the SES, but the engine will run near normal. Many times, no difference in performance is noticed.