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 the fuel tank pressure (FTP) sensor voltage with the Honda PGM Tester, or measure voltage between ECM/PCM connector terminals E4 and E14.
   Fig 1: Measuring Voltage Between ECM/PCM Connector Terminals E4 & E14

   

   Is there about 2.5V? 

   1. YES  - Go to step 4.
   2. 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 that hose.
   Fig 2: Connecting Vacuum Pump To Open End Hose

   
7. Turn the ignition switch ON (II).
8. Monitor the FTP sensor voltage with the Honda PGM Tester, or measure voltage between ECM/PCM connector terminals E4 and E14, and carefully squeeze the vacuum pump a little.
   Fig 3: Measuring Voltage Between ECM/PCM Connector Terminals E4 & E14

   
9. The voltage should smoothly drop from about 2.5 V down 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? 

   1. YES  - Reprogram the ECM/PCM if it does not have the latest software, or substitute a known-good ECM/PCM, then recheck (see ECM/PCM REPROGRAMMING AND SUBSTITUTION FOR TESTING ). If the symptom/indication goes away with a known-good ECM/PCM, replace the original ECM/PCM.
   2. NO  - Replace the FTP sensor.