DTC P0451: FTP Sensor Range/Performance Problem

Special Tools Required 

Vacuum pump/gauge, 0-30 in.Hg A973X-041-XXXXX

1. Remove the fuel fill cap.
2. Turn the ignition switch ON (II).
3. Monitor fuel tank pressure (FTP) sensor voltage with the HDS or a scan tool, or measure voltage between ECM connector terminals E4 and E14.
   Fig 1: Measuring Voltage Between ECM Connector Terminals E4 And E14

   Courtesy of AMERICAN HONDA MOTOR CO., INC.

   Is there about 2.5V? 

   YES:  Go to step 4.

   NO:  Replace the FTP sensor.

4. Turn the ignition switch OFF.
5. Disconnect the hose between the EVAP two way valve and the FTP sensor at the EVAP two way valve end.
6. Connect a vacuum pump to the open end of the hose.
   Fig 2: Connecting A Vacuum Pump To The Open End Of The Hose

   Courtesy of AMERICAN HONDA MOTOR CO., INC.
7. Turn the ignition switch ON (II).
8. Monitor FTP sensor voltage with the HDS or a scan tool, or measure voltage between ECM connector terminals E4 and E14, and carefully squeeze the vacuum pump a little.
   Fig 3: Measuring Voltage Between ECM Connector Terminals E4 And E14

   Courtesy of AMERICAN HONDA MOTOR CO., INC.
9. The voltage should smoothly drop from about 2.5 V to about 1.5 V. Stop applying vacuum when the voltage drops to about 1.5 V or damage to the FTP sensor may occur.

   Does the voltage drop to about 1.5 V and hold? 

   YES:  Check for misrouted, leaking, or broken FTP sensor vacuum lines. If the vacuum lines are OK, update the ECM if it does not have the latest software, or substitute a known-good ECM, then recheck (see ECM UPDATING AND SUBSTITUTION FOR TESTING ). If the symptom/indication goes away with a known-good ECM, replace the original ECM.

   NO:  Replace the FTP sensor.