DTC P0451: FTP Sensor Circuit Range/Performance Problem

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.
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 commercially available vacuum pump/gauge, 0-30 in.Hg, to the open end of the hose.
   Fig 2: Connecting Vacuum Pump/Gauge, 0-30 In.Hg, To Open End Of Hose

   Courtesy of AMERICAN HONDA MOTOR CO., INC.
7. Turn the ignition switch ON (II).
8. Monitor FTP sensor voltage with the HDS, or measure voltage between ECM connector terminals A29 and C18, and slowly squeeze the vacuum pump/gauge.
   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 FTP sensor may occur.

   Does the voltage drop to about 1.5 V and hold? 

   1. YES -  Intermittent failure, system is OK at this time. Check for poor connections at the FTP sensor and the ECM.
   2. NO -  Replace the FTP sensor.