What is a PO455 code, I have heard that it can be a loose gas cap or something with the vaccume lines, any help would be appreciated. Oh and also could this be causing a PO300 code?

Sorry for the long post but here is all the info and bs to firgure it out. Prolly wont be able to do it your self but check the obvious first.


P0455 = Evap System Large Leak Detected.

DTC P0455: EVAP SYSTEM LARGE LEAK DETECTED

DTC Set Criteria

DTC will set under following conditions: Less than 16 minutes have passed since engine started. Engine coolant temperature was less than 86°F (30°C) when engine started, and more than 140°F (60°C) when monitor begins. Intake air temperature was 86°F (30°C) or less when engine started, and more than 41°F (5°C) during monitor. Engine speed is more than 1600 RPM. Power steering pressure switch is off. Barometric pressure is more than 11 psi (76 kPa). Volumetric efficiency is 20-80 percent (2.4L) or 25-80 percent (3.0L). Vehicle speed is 19 MPH or more. Monitor runs 75-125 seconds depending on fuel level and fuel tank temperature. Code will set if internal pressure of fuel tank fluctuates less than .047 psi. (.324 kPa) in 20 seconds after purge solenoid is driven when fuel tank and vapor lines are closed.
Probable Causes

• Loose fuel cap.
• Defective fuel cap relief valve or incorrect relief pressure.
• Fuel overflow limiter valve failed.
• Purge line or vapor line is clogged.
• Fuel tank, purge line or vapor line leaks.
• Purge solenoid failed.
• Ventilation solenoid failed.
• Fuel Tank Differential Pressure (FTDP) sensor failed.
• Clogged or leaking EVAP canister.
• Use of incorrect fuel.

Diagnostic Procedure (3.0L)


NOTE:
The following test procedure requires functions available on manufacturer's MUT-II scan tool. Generic scan tools may not have the capability to carry out test. An improperly tightened fuel cap can cause this code to set. Check for properly installed fuel cap and a good seal between the fuel cap and fuel filler neck.
1. Disconnect hose "A" at intake manifold end. See Fig. 68 . Connect hand vacuum pump to hose "A". Apply 12 in. Hg (40 kPa) or less of vacuum. If vacuum holds, go to step 3 . If vacuum leaks, go to next step.
2. Using hand vacuum pump, check hose "A" for leaks. If leak exists, replace hose "A", then go to step 31 . If problem does not exist, replace purge solenoid, then go to step 31 .
3. Disconnect hose "C" from purge solenoid. See Fig. 56 . Turn ignition on. Using scan tool, select actuator test item No. 8 (purge solenoid) and turn on (open) purge solenoid. Vacuum should return to atmospheric pressure. If purge solenoid operates and vacuum returns to atmospheric pressure, go to step 5 . If purge solenoid operates and vacuum does not return to atmospheric pressure, go to next step. If purge solenoid does not operate, see DTC P0443: EVAPORATIVE EMISSION (EVAP) SYSTEM PURGE SOLENOID CIRCUIT MALFUNCTION .
4. Exit actuator test. Using hand vacuum pump, check hoses "A" and "B" for clogging. See Fig. 59 and Fig. 68 . If clogging exists, replace appropriate hose, then perform purge flow check. See PURGE CONTROL SYSTEM CHECK (PURGE FLOW CHECK) under FUEL EVAPORATION under EMISSION SYSTEMS & SUB-SYSTEMS in SYSTEM & COMPONENT TESTING article. If clogging does not exist, replace purge solenoid, then go to step 31 .
5. Connect hoses "A", "B", and "C". Remove vent valve module bracket mounting bolts. Disconnect hose "G" from ventilation solenoid. Connect hand vacuum pump to ventilation solenoid. See Fig. 57 . Apply vacuum to ventilation solenoid. Vacuum should leak. Using scan tool, select actuator test item No. 29 (ventilation solenoid) and turn on (close) ventilation solenoid. Apply vacuum to ventilation solenoid. Vacuum should hold. If ventilation solenoid performs as specified, go to next step. If ventilation solenoid operates, but vacuum leaks when ventilation solenoid is turned on (closed), replace ventilation solenoid, then go to step 31 . If ventilation solenoid operates, but vacuum does not leak when ventilation solenoid is turned off (opened), locate and repair clogging between ventilation solenoid and air intake, then go to step 31 . If ventilation solenoid does not operate, go to DTC P0446: EVAPORATIVE EMISSION (EVAP) SYSTEM VENT CONTROL MALFUNCTION .

NOTE:
Before pressure testing, confirm Miller EVAP System Pressure Pump (6872A) is operating properly. Perform self-test procedures described in manufacturer's instructions.
6. Exit actuator test. Plug end of hose "G" that was disconnected from ventilation solenoid. Connect EVAP system pressure pump to fuel filler neck. Pressure test system by performing I/M240 simulation test described in EVAP system pressure pump manufacturer's instructions located in lid of pump box. If leak is indicated, go to next step. If leak is not indicated, go to step 19 .
7. Disconnect and plug hose "I" at EVAP canister side. See Fig. 58 . Repeat pressure test. If leak is indicated, go to step 11 . If no leak is indicated, go to next step.
8. Using hand vacuum pump, check for leaks in hoses "C" through "E". See Fig. 59 and Fig. 60 . If leak exists, replace appropriate hose, then go to step 31 . If leak does not exist, go to next step.
9. Remove fuel tank. Using hand vacuum pump, check for vacuum leaks in hoses "F" through "H". See Fig. 61 . If problem exists, replace appropriate hose(s), install fuel tank, then go to step 31 . If problem does not exist, go to next step.
10. Connect hand vacuum pump to EVAP canister port from which hose "G" was disconnected. Plug other 2 EVAP canister ports. Apply vacuum. If vacuum holds, install fuel tank, then go to step 31 . If vacuum does not hold, replace EVAP canister, install fuel tank, then go to step 31 .
11. Remove fuel filler neck assembly. Using hand vacuum pump, check hoses "I", "L", "M", "N" and "O" for leaks. See Fig. 62 and Fig. 63 . If leak exists, replace appropriate hose(s), install fuel filler neck, then go to step 31 . If leak does not exist, go to next step.
12. Remove check valve "A". Blow on check valve "A" in both directions. Check valve "A" should leak air only in direction shown in illustration. See Fig. 50 . If check valve "A" passes air as indicated, go to next step. If check valve "A" does not pass air as indicated, replace check valve "A", install fuel filler neck and go to step 31 .
13. Remove check valve "B". Blow on check valve "B" in both directions. Check valve "B" should pass more air in one direction than the other as shown in illustration. See Fig. 51 . If check valve "B" passes air as indicated, go to next step. If check valve "B" does not pass air as indicated, replace check valve "B", install fuel filler neck and go to step 31 .
14. Disconnect hose "J" at liquid separator end and connect hand vacuum pump to hose "J". See Fig. 64 . Disconnect and plug hose "K" at fuel tank end. See Fig. 65 . Apply vacuum. If vacuum leaks, go to step 18 . If vacuum does not leak, go to next step.
15. Remove fuel tank. Using hand vacuum pump, check hose "P" for leaks. See Fig. 66 . If problem exists, replace hose "P", install fuel tank and fuel filler neck, then go to step 31 . If problem does not exist, go to next step.
16. Visually check fuel tank for cracks and leaks. Connect EVAP system pressure tester to leveling valve port. See Fig. 66 . Securely plug all fuel tank openings. Using EVAP system pressure tester, apply pressure. Using soapy water, check each section of fuel tank for leaks. If leak exists, repair leak as necessary, install fuel tank and fuel filler neck, then go to step 31 . If leak does not exist, go to next step.
17. Visually check fuel filler neck for cracks. If leak exists, replace fuel filler neck assembly, install fuel tank and go to step 31 . If leak does not exist, install fuel tank and fuel filler neck, then go to step 31 .
18. Using hand vacuum pump, check hoses "J" and "K" and pipe between hoses "J" and "K" for leaks. See Fig. 67 . If leak exists, replace appropriate hose(s) or pipe, install fuel filler neck, then go to step 31 . If leak does not exist, install fuel filler neck, then go to step 31 .
19. Remove plug from hose "G". On EVAP system pressure pump, set pressure/hold valve to OPEN and set vent valve to CLOSED. Turn pump timer on. Air should pass through hose "G". If air passes through hose "G", go to step 23 . If air does not pass through hose "G", go to next step.
20. Disconnect hose "I" at EVAP canister side. See Fig. 58 . On EVAP system pressure pump, set pressure/hold valve to OPEN and set vent valve to CLOSED. Turn pump timer on. Air should pass through hose "I". If air passes through hose "I", go to next step. If air does not pass through hose "I", go to step 26 .
21. Remove fuel tank. Using hand vacuum pump, check hoses "H" and "G" for clogging. See Fig. 61 . If problem exists, replace appropriate hose(s), install fuel tank, then go to step 33 . If problem does not exist, go to next step.
22. Connect hand vacuum pump to EVAP canister port from which hose "G" was disconnected. Plug other 2 EVAP canister ports. Apply vacuum. Unplug ports in turn. Each port should leak vacuum. If vacuum holds when either port is unplugged, replace EVAP canister, install fuel tank, then go to step 33 . If vacuum leaks, install fuel tank and go to step 31 .
23. Disconnect hose "F" at floor pipe side. See Fig. 61 . Connect hand vacuum pump to floor pipe. Apply 12 in. Hg (40 kPa) or less of vacuum. Using scan tool, select actuator test item No. 8 (purge solenoid) and turn on (open) purge solenoid valve. If vacuum leaks, go to step 25 . If vacuum does not leak, go to next step.
24. Using hand vacuum pump, check hoses "C" through "E" for clogging. See Fig. 59 and Fig. 60 . If problem exists, replace appropriate hose(s), then perform purge flow check. See PURGE CONTROL SYSTEM CHECK (PURGE FLOW CHECK) under FUEL EVAPORATION under EMISSION SYSTEMS & SUB-SYSTEMS in SYSTEM & COMPONENT TESTING article. If problem does not exist, go to next step.
25. Remove fuel tank. Using hand vacuum pump, check hose "F" and EVAP canister for clogging. See Fig. 61 . Replace hose "F" or EVAP canister as necessary, install fuel tank, then go to step 33 .
26. Remove fuel filler neck assembly. Using hand vacuum pump, check hoses "I" and "L" through "O" for clogging. See Fig. 62 and Fig. 63 . If problem exists, replace appropriate hose(s), install fuel filler neck and fuel tank as necessary, then go to step 33 . If problem does not exist, go to next step.
27. Remove check valve "A". Blow on check valve "A" in both directions. Check valve "A" should leak air only in direction shown in illustration. See Fig. 50 . If check valve "A" passes air as indicated, go to next step. If check valve "A" does not pass air as indicated, replace check valve "A", install fuel filler neck and fuel tank as necessary, then go to step 33 .
28. Remove check valve "B". Blow on check valve "B" in both directions. Check valve "B" should pass more air in one direction than the other as shown in illustration. See Fig. 51 . If check valve "B" passes air as indicated, go to next step. If check valve "B" does not pass air as indicated, replace check valve "B", install fuel filler neck and fuel tank as necessary, then go to step 33 .
29. Using hand vacuum pump, check hoses "J" and "K" and pipe between hoses "J" and "K" for clogging. See Fig. 67 . If problem exists, replace appropriate hose or pipe, install fuel filler neck and fuel tank as necessary, then go to step 33 . If problem does not exist, go to next step.
30. Remove fuel tank if not previously removed. Using hand vacuum pump, check hose "P" for clogging. See Fig. 66 . If problem exists, replace hose "P", install fuel tank and fuel filler neck, then go to step 33 . If problem does not exist, install fuel tank and fuel filler neck, then go to next step.
31. Ensure fuel cap is tightened 3 clicks. Turn ignition on. Using scan tool, clear DTCs. Start engine and let idle. Start EVAP system leak monitor test using MUT-II scan tool. Select SYSTEM TEST and press YES key. Select EVAP LEAK MON and press YES key. During monitor, keep accelerator pedal in idling position. Item IN PROGRESS is displayed during monitor. IN PROGRESS will change from NO to YES by keeping engine speed and load within defined range. Go next step.

NOTE:
If engine speed does not reach 2000 RPM during monitor, adjustment of fixed Speed Adjusting Screw (SAS) may be needed. See FIXED SPEED ADJUSTING SCREW under IDLE SPEED & MIXTURE in ON-VEHICLE ADJUSTMENTS article.
32. If EVAP LEAK MON. COMPLETED. TEST PASSED is displayed, EVAP system currently is working properly. Code was probably set by improperly installed fuel cap. If EVAP LEAK MON. COMPLETED. TEST FAILED & DTCS SET is displayed, go to step 1 . If EVAP LEAK MON. DISCONTINUED. RETEST AGAIN FROM THE FIRST is displayed, turn ignition off, and repeat monitor. Go to step 31 .
33. Test drive vehicle following OBD-II drive cycle EVAP system leak monitor pattern. See EVAP SYSTEM LEAK MONITOR under OBD-II DRIVE CYCLES under VERIFYING REPAIRS. Check for DTCs. If DTC P0455 is output, retry diagnostic procedure. If DTC P0455 is not output, inspection is complete.






P0300


DTC P0300: RANDOM MISFIRE DETECTED

DTC Set Criteria

At least 5 seconds have passed since engine started. Engine speed is 500-6000 RPM (2.4L) or 440-6000 RPM (3.0L). Engine coolant temperature is more than 14°F (-10°C). Intake air temperature is more than 14°F (-10°C). Barometric pressure is more than 11 psi (76 kPa). Adaptive learning is complete for the vane which generates crankshaft position signal. Engine is running and there is no gear shifting, deceleration, sudden acceleration or A/C compressor switching occurring. Vehicle speed is 1.6 MPH or more. Throttle deviation is -59-59 millivolts per 10 milliseconds. Misfire is determined by change in angular velocity of Crankshaft Position (CKP) sensor. Code will set if misfire occurred in 4 or more of last 200 revolutions when catalytic converter temperature is more than 1742°F (950°C) (severe misfire which will cause MIL to flash continuously). Also, code will set if misfire occurred in 20 or more of last 1000 revolutions.
Probable Causes

• Ignition system related part(s) failed.
• Poor CKP sensor signal.
• Incorrect air/fuel ratio.
• Low compression pressure.
• Timing belt jumped or teeth broken.
• EGR system failed.
• Engine Control Module/Powertrain Control Module (ECM/PCM) failed.




Diagnostic Procedures (3.0L)

1. Start engine and let idle. Using scan tool, check data list item No. 22 (crankshaft position sensor). Check waveform of CKP sensor pulse width by keeping engine speed constant. If CKP sensor pulse width is constant, go to next step. If CKP sensor pulse width is not constant, check CKP sensor circuit. See DTC P0335: CRANKSHAFT POSITION (CKP) SENSOR CIRCUIT MALFUNCTION .
2. Ensure engine is at normal operating temperature. Turn all accessories off. Increase engine speed to 2500 RPM. Using scan tool, check data list item No. 81 (long-term fuel compensation). At 2500 RPM in closed loop, fuel trim should be -12.5-12.5 percent. If fuel trim is as specified, go to next step. If fuel trim is not as specified, check fuel trim fault. See DTC P0171 OR P0174: SYSTEM TOO LEAN or DTC P0172 OR P0175: SYSTEM TOO RICH .
3. Using scan tool, check data list item No. 82 (short-term fuel compensation). At 2500 RPM in closed loop operation, fuel trim should be -25.0-25.0 percent. If fuel trim is as specified, go to next step. If fuel trim is not as specified, check fuel trim fault. See DTC P0171 OR P0174: SYSTEM TOO LEAN or DTC P0172 OR P0175: SYSTEM TOO RICH .
4. Remove spark plugs and connect to plug wire. Ground spark plug electrode and crank engine. If spark plug fires when engine is cranked, go to step 7 . If spark plug does not fire, go to next step.

NOTE:
DO NOT adjust gap on platinum plugs.
5. Check spark plug gap. Gap should be .039-.043" (1.0-1.1 mm). If problem exists, adjust gap orreplace plugs, then go to step 14 . If problem does not exist, go to next step.
6. Remove plug wires and measure resistance. Maximum resistance for each plug wire is 22 k/ohms. If any plug wire resistance is more than specified, replace appropriate plug wire, then go to step 14 . If plug wire resistances are okay, check ignition circuit. See IGNITION CHECKS in BASIC DIAGNOSTIC PROCEDURES article. If problem exists, repair as necessary. If problem does not exist, go to next step.
7. Disconnect left bank fuel injector connectors (fuel injectors No. 2, 4, and 6). Measure resistance between fuel injector connector terminals (component side). Disconnect right bank fuel injector 4-pin intermediate connector B-48. Measure resistance between fuel injector intermediate connector (component side) terminals No. 1 and 2 (fuel injector No. 1), No. 1 and 3 (fuel injector No. 3), and No. 1 and 4 (fuel injector No. 5). See Fig. 19 . Resistance should be 13-16 ohms at 68°F (20°C). If each resistance is as specified, go to step 9 . If fuel injector No. 2, 4 or6 resistance is not as specified, replace appropriate fuel injector(s), then go to step 14 . If fuel injector No. 1, 3 or5 resistance is not as specified, go to next step.
8. Remove intake manifold. Disconnect connector to fuel injector that failed previous step. Measure resistance between fuel injector connector terminals (component side). Resistance should be 13-16 ohms at 68°F (20°C). If resistance is as specified, repair wire between fuel injector and intermediate connector, install intake manifold and go to step 14 . If resistance is not as specified, replace fuel injector, install intake manifold and go to step 14 .
9. Check left bank fuel injector connectors and right bank fuel injector intermediate connector for loose, damaged or corroded terminals. If problem exists, repair connector, then go to step 14 . If problem does not exist, go to next step.
10. Disconnect ECM connector C-51 or PCM connector C-52. Check ECM connector C-51 or PCM connector C-52 for loose, damaged or corroded terminals. If problem exists, repair appropriate connector, then go to step 14 . If problem does not exist, go to next step.
11. Check for damage to wiring between fuel injectors and ECM/PCM. To check wiring between fuel injector intermediate connector and right bank fuel injectors, it will be necessary to remove intake manifold. If problem exists, repair as necessary, then go to step 14 . If problem does not exist, go to next step.
12. Check valve timing. See appropriate article in ENGINES. Check engine compression. See MECHANICAL INSPECTION under PRELIMINARY INSPECTION & ADJUSTMENTS in BASIC DIAGNOSTIC PROCEDURES article. Check EGR system. See EXHAUST GAS RECIRCULATION (EGR) under EMISSION SYSTEMS & SUB-SYSTEMS in SYSTEM & COMPONENT TESTING article. If problem exists, repair as necessary, then go to step 14 . If problem does not exist, go to next step.
13. Replace all fuel injectors. Test drive vehicle following OBD-II drive cycle other monitor pattern. See OTHER MONITOR under OBD-II DRIVE CYCLES under VERIFYING REPAIRS. Check for DTCs. If DTC P0300 is output, replace ECM/PCM, then go to next step. If DTC P0300 is not output, inspection is complete.
14. Test drive vehicle following OBD-II drive cycle other monitor pattern. See OTHER MONITOR under OBD-II DRIVE CYCLES under VERIFYING REPAIRS. Check for DTCs. If DTC P0300 is output, retry diagnostic procedure. If DTC P0300 is not output, inspection is complete.



Here is a brief overview of it all, again check the obvious and simple stuff first. This is just to give you an idea of what you need to check.

Although to most this post will be worthless to us who are a bit more mechanically understanding it will make some sense. Good luck!

ur fuel cap is loose, it happens to eclipses ALLLLLLLLLL the time.

Yea that's what the mechanic said, now my problem is that I want a locking cap but i cant find one anyone know where to get one that fits the eclipse without a misfit one from autozone?

Try google, that would be your best bet probably. Just be careful of a site you order it from.

Well the thing is, I bought one about 3 months ago to replace my old one because some punk kid cut my old one off. So I went up to AutoZone to get a locking cap, well I bought another one, different brand but still locking and I still have the code up, so could it be something worst??