DTC P0451: EVAP SYSTEM PRESSURE SENSOR RANGE/PERFORMANCE PROBLEM Subaru Outback BH

Perform basic diagnostic procedure. See BASIC DIAGNOSTIC PROCEDURE . If any other DTCs are set, diagnose and repair those DTCs first. If DTC P0451 is only DTC set, turn ignition off. Check fuel filler cap for tightness. Check for disconnected, leaking or plugged vacuum hoses and pipes between fuel tank and fuel tank pressure sensor. Check for disconnected, leaking or plugged air ventilation hoses and pipes between fuel tank and fuel filler pipe. Repair or replace components as necessary. If all components are okay, replace fuel tank pressure sensor. Clear memory and perform verification procedure. See CLEARING DIAGNOSTIC TROUBLE CODES and VERIFICATION PROCEDURE .

Scheme 69

1. Perform basic diagnostic procedure. See «BASIC DIAGNOSTIC PROCEDURE»(ref-63535-S26517940312001020900000). Turn ignition off. Remove and reinstall fuel filler cap. Turn ignition on. Using scan tool, observe fuel tank pressure. If pressure is less than -0.83 in. Hg, go to next step. If pressure is not less than -0.83 in. Hg, system has returned to normal. Check for intermittent open or short in wiring or poor terminal contact in connectors between fuel tank pressure sensor and ECM. See WIRING DIAGRAMS article.
2. Using a DVOM connected to ground, backprobe ECM connector B135 (28-pin connector) terminal No. 9. see scheme 4 If voltage is more than 4.5 volts, go to step 4. If voltage is not more than 4.5 volts, go to next step.
3. Using a DVOM connected to ground, backprobe ECM connector B135 (28-pin connector) terminal No. 9 while wiggling harness and ECM connector. If voltage changes more than 4.5 volts while wiggling harness and ECM connector, locate and repair open circuit in wiring and check for poor terminal contact in connectors between ECM and fuel tank pressure sensor. If voltage does not change more than 4.5 volts while wiggling harness and ECM connector, contact authorized Subaru dealership because probable cause is deterioration of multiple parts.
4. Using a DVOM connected to ground, backprobe ECM connector B135 (28-pin connector) terminal No. 15. If voltage is less than 0.2 volt, go to step 6. If voltage is not less than 0.2 volt, go to next step.
5. Using scan tool, observe fuel tank pressure while wiggling harness and ECM connector. If pressure changes more than -0.83 in. Hg while wiggling harness and ECM connector, check for poor terminal contact at ECM connector. If pressure does not change more than -0.83 in. Hg while wiggling harness and ECM connector, go to next step.
6. Turn ignition off. Move rear seat cushion and disconnect Gray 6-pin in-line connector located between rear wiring harness and fuel tank harness. Turn ignition on. Check voltage between ground and ECM-side of Gray 6-pin in-line connector terminal No. 5. see scheme 13If voltage is more than 4.5 volts, go to next step. If voltage is not more than 4.5 volts, locate and repair open circuit in wiring and check for poor terminal contact in connectors between ECM and Gray 6-pin in-line connector. See WIRING DIAGRAMS article.
7. Turn ignition off. Disconnect ECM connector B135 (28-pin connector). Using an ohmmeter, measure resistance between ECM connector B135 (28-pin connector) terminal No. 19 and ECM-side of Gray 6-pin in-line connector terminal No. 1. If resistance is less than one ohm, go to next step. If resistance is not less than one ohm, locate and repair open circuit in wiring and check for poor terminal contact in connectors between ECM and Gray 6-pin in-line connector. See WIRING DIAGRAMS article.
8. Measure resistance between ground and ECM-side of Gray 6-pin in-line connector terminal No. 1. If resistance is more than 500 k/ohms, go to next step. If resistance is not more than 500 k/ohms, locate and repair short to ground in wiring between ECM and Gray 6-pin in-line connector.
9. Disconnect fuel tank pressure sensor connector. Measure resistance between fuel tank pressure sensor harness connector terminal No. 3 and fuel-tank side of Gray 6-pin in-line connector terminal No. 5. see scheme 6and (Scheme 69). If resistance is less than one ohm, go to next step. If resistance is not less than one ohm, locate and repair open in fuel tank harness.
10. Measure resistance between fuel tank pressure sensor harness connector terminal No. 1 and fuel-tank side of Gray 6-pin in-line connector terminal No. 1. If resistance is less than one ohm, go to next step. If resistance is not less than one ohm, locate and repair open in fuel tank harness.
11. Measure resistance between ground and fuel tank pressure sensor harness connector terminal No. 2. If resistance is more than 500 k/ohms, go to next step. If resistance is not more than 500 k/ohms, locate and repair short to ground in fuel tank harness.
12. Check for poor terminal contact at fuel tank pressure sensor connector. If terminal contact is okay, replace fuel tank pressure sensor. Clear memory and perform verification procedure. See «CLEARING DIAGNOSTIC TROUBLE CODES»(ref-63535-S26931138132001020900000) and «VERIFICATION PROCEDURE»(ref-63535-S38101445392001020900000).