DTC P1091: Rail Pressure (RP) Control Valve Circuit Open
- Check the ''On Board Diagnostic (OBD) System Check''.
Was the ''OBD System Check'' performed?
YES – Go to step 2.
NO – Go to OBD System Check. 
- Check the DTC.
Are there any other DTCs (beside DTC) being output?
YES – Go to relevant chart.
NO – Go to step 3.
- Check for the following conditions:
- Damaged the fuel metering unit.
Is a problem found?
YES – Repair as necessary (Replace the fuel supply pump).
NO – Go to step 4.
- Turn the ignition switch OFF.
- Disconnect ECM connector.
- Check the fuel metering unit signal circuit for an open.
Wire side of female terminals
Injector 2P connector
JUMPER WIRE
Is a problem found?
YES – Repair the fuel metering unit circuit.
NO – Go to step 14.
- Measure the resistance of fuel metering unit as below.
Is the resistance value 2.5 – 3.2 ohms? (At room temperature)
YES – Substitute a known-good ECM and recheck. If symptom/indication goes away, replace the original ECM.
NO – Replace the supply pump.
| NOTICE |
The battery power supply short circuit to 5 V power supply damages the ECM.