GDI ECM operates fuel pressure regulator (spill valve) with the signal from fuel rail pressure sensor to control optimized RPM and rail pressure.
High pressure pump adds high pressure to low pressure fuel from low pressure pump. Controling fuel pressure is done by fuel pressure regulator from 40 to 150 bar. Under the abnormal condition of high pressure fuel system, ECM contols fuel system as low pressure.
When ECM detects short to ground in the spill valve control circuit, ECM sets DTC P0091.
Item
Detecting Condition
Possible cause
DTC Strategy
Signal check
Poor Connection
Short to ground in fuel pressure regulator(spill valve) circuit
Enable Conditions
No disabling Faults Present
Normal IDB supply voltage
Threshold value
Short to ground circuit
Diagnosis Time
5 sec.
MIL On Condition
2 Drive Cycles
Fig.1) Normal waveform of spill valve at idle.