Component Location
General Description
Common rail Euro-III engine controls fuel pressure with one control valve which controls inlet or outlet of fuel line. Inlet control type has disadvantage of activating fast increase of fuel pressure when initial starting or sudden acceleration because the procedure to get high fuel pressure takes many steps like low pressure pump ? control valve ? high pressure pump ? common rail. However, outlet control type has advantage of quick increase of fuel pressure but there are weak point such as loss of engine power and fuel temperatures up. Therefore, CRDi Euro-IV has been adopted "Dual Pressure Control type" so that precise and quick increase of fuel pressure can be easily established with various engine condition. Dual Pressure Control" type means that CRDi Euro-IV engine has the inlet pressure from high pressure pump and outlet pressure of common rail simultaneously.
Fuel pressure gets high if fuel pressure control valve(P-PRV, Pump Pressure Regulating Valve) installed between low pressure pump and high pressure pump(inlet side) closes the fuel line with increased duty values controlled by ECM. With rail pressure control valve(PRV, Pressure Regulator Valve), the higher duty values from ECM the higher rail pressure is set because it closes outlet of common rail.
ECM controls current for Both P-PRV installed on high pressure pump and PRV installed on common rail after sensing RPS installed on common rail so that CRDi engine gets optimum rail pressure control corresponding with current engine RPM and load condition. If the condition that is out of target rail pressure is occurred due to mechanical or electrical problem, ECM controls fuel amount to minimum limit to get limp home and set DTC. The relevant to this DTC is to indirectly diagnose mechanical operating condition of feed line of low pressure, high pressure pump, P-PRV and PRV etc. through out the current value of P-PRV, PRV and RPS output value.
DTC Description
Rail pressure is controlled by 1)only RPRV or 2)both RPRV and FPRV or 3)only RPRV depending on engine condition. These three modes are called ‘CPC mode’. During transition from one mode to another mode, if rail pressure is below the minimum rail pressure for each certain engine condition for more than 300ms. P1171 is set then, rail pressure is controlled by RPRV alone.
DTC Detecting Condition
Item | Detecting Condition | Possible Cause |
DTC Strategy | Signal monitoring
| ECM internal error
RPRV component
FPRV component
RPS componet
|
Enable Conditions | Engine running
|
Threshold Value | If rail pressure is below the minimum rail pressure for each certain engine condition
|
Diagnostic Time | 0.3 sec.
|
Fail Safe | Fuel cut | NO | -
|
EGR Off | NO |
Fuel Limit | NO |
Check Lamp | ON |