DTC P0451: FTP Sensor Circuit Range/Performance Problem (2002-2004 models)

Special Tools Required 

Vacuum pump/gauge, 0-30 in.Hg, Snap-on YA4000A or equivalent, commercially available

1. Remove the fuel fill cap.
2. Turn the ignition switch ON (II).
3. Monitor the fuel tank pressure (FTP) sensor voltage with the HDS, or measure voltage between ECM/PCM connector terminals E4 and E14.
   Fig 1: Removing Fuel Fill Cap

   Courtesy of AMERICAN HONDA MOTOR CO., INC.

   Is there about 2.5 V? 

   1. YES -  Go to step 4.
   2. NO -  Replace the FTP sensor (see FTP SENSOR REPLACEMENT  ).
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 the vacuum pump/gauge, 0-30 in.Hg, to the open end of that hose.
   Fig 2: Connecting Vacuum Pump/Gauge

   Courtesy of AMERICAN HONDA MOTOR CO., INC.
7. Turn the ignition switch ON (II).
8. Monitor the FTP sensor voltage with the HDS, or measure voltage between ECM/PCM connector terminals E4 and E14, and slowly squeeze the vacuum pump/gauge. Stop applying vacuum when the voltage drops to about 1.5 V or damage to the FTP sensor may occur.
   Fig 3: Monitoring FTP Sensor Voltage

   Courtesy of AMERICAN HONDA MOTOR CO., INC.
9. The voltage should drop smoothly from about 2.5 V down to about 1.5 V.

   Does the voltage drop to about 1.5 V and hold? 

   1. YES -  Update the ECM/PCM if it does not have the latest software, or substitute a known-good ECM/PCM (see HOW TO UPDATE THE ECM/PCM ), then recheck. If the symptom/indication goes away with a known-good ECM/PCM, replace the original ECM/PCM (see ECM/PCM REPLACEMENT ).
   2. NO -  Replace the FTP sensor (see FTP SENSOR REPLACEMENT  ).