DTC P0451 '99-00, '02-04 Models: FTP Sensor Range/Performance Problem

Special Tools Required 

1. 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 FTP sensor voltage with the HDS, or measure voltage between PCM connector terminals A29 and C18.
   Fig 1: Measuring Voltage Between PCM Connector Terminals A29 & 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 vacuum pump to the open end of the hose.
   Fig 2: Connecting Vacuum Pump To The Open 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 PCM connector terminals A29 and C18, and slowly squeeze the vacuum pump one stroke at a time.
   Fig 3: Measuring Voltage Between PCM Connector Terminals A29 & C18

   Courtesy of AMERICAN HONDA MOTOR CO., INC.
9. The voltage should drop smoothly 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:  Check for misrouted, leaking, or broken FTP sensor vacuum lines. If the vacuum lines are OK, substitute a known-good PCM and recheck (see HOW TO SUBSTITUTE THE PCM FOR TESTING PURPOSE ). If the symptom/indication goes away, replace the original PCM.
   2. NO:  Replace the FTP sensor.