DTC P0451: FTP Sensor Circuit Range/Performance Problem (2000-2005 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 FTP sensor voltage with the HDS, or measure voltage between ECM connector terminals A29 and C18.
   Fig 1: Measuring Voltage Between ECM Connector Terminals A29 And C18

   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 fuel tank pressure sensor (A) at the EVAP two-way valve end.
   Fig 2: Disconnecting Hose Between EVAP Two-Way Valve And Fuel Tank Pressure Sensor At EVAP Two-Way Valve End

   Courtesy of AMERICAN HONDA MOTOR CO., INC.
6. Connect a vacuum pump/gauge, 0-30 in.Hg, to the open end of the hose.
7. Turn the ignition switch ON (II).
8. Monitor the FTP sensor voltage with the HDS, or measure voltage between ECM connector terminals A29 and C18, and carefully squeeze the vacuum pump a little.
   Fig 3: Measuring Voltage Between ECM Connector Terminals A29 And C18

   Courtesy of AMERICAN HONDA MOTOR CO., INC.
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 fuel tank pressure sensor may occur.

   Does the voltage drop to about 1.5 V and hold? 

   1. 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; 2000-2001 M/T models (see HOW TO TROUBLESHOOT CIRCUITS AT THE ECM ), 2002-2005 M/T models and CVT model (see ECM UPDATING AND SUBSTITUTION FOR TESTING-2006 M/T MODELS AND CVT MODEL ), then recheck. If the symptom/indication goes away with a known-good ECM, replace the original ECM (see ECM REPLACEMENT ).
   2. NO  -Replace the FTP sensor (see FTP SENSOR REPLACEMENT ).