Mechanics

TROUBLE SHOOTING CODE!

1999 GMC Sierra

Computer problem
1999 GMC Sierra V8 Four Wheel Drive Automatic

I own a code reader and it threw out the code P0442! What things should I check to diagnose this? I know my gas cap is one thing, but what else would trigger that code? My check engine light is constantly on and when I try to reset it it comes right back on!
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Mr_SirGuardian82
October 29, 2009.




Circuit Description
Conditions for setting DTC:





No ECT, HO2S, IAT, MAP, ODM, TP or VSS sensor DTCs set. DTC P0125 not active. Fuel level 12.5-87.5 percent. Vacuum decay for a period of at least 15 seconds. Vacuum less than 7 in. H2O for less than 25 seconds. Vacuum greater than 0.1 in. H2O for longer than 35 seconds.

Diagnostic Procedures

Page 1 of 2
EVAP emission system includes the following components: fuel tank, EVAP vent solenoid, fuel tank pressure sensor, fuel pipes and hoses, vapor lines, fuel cap, EVAP emission canister, purge lines, and EVAP purge solenoid.
1. Perform On-Board Diagnostic (OBD) system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step. 2. Check if DTC P0446, P0452 or P0453 is set. If any of this DTC is set, diagnose affected DTC. If DTCs are not set, go to next step. 3. Turn ignition off. Remove fuel cap. Turn ignition on. Using scan tool, read FUEL TANK VACUUM. If scan tool displays zero in. H2O go to next step. If scan tool does not display zero in. H2O, repair faulty fuel tank sensor circuit. 4. Zero pressure and vacuum gauges on EVAP Pressure/Purge Diagnostic Station (J-41413). Reinstall fuel cap. Read and Record FAILURE RECORDS data for this DTC. Clear DTCs. Using scan tool, command EVAP vent valve on (closed). Connect EVAP Pressure/Purge Diagnostic Station (J-41413) to EVAP service port. Using diagnostic station, pressurize EVAP system to 15 in. H2O. Monitor pressure on diagnostic station gauge. If pressure decreases to less than 10 in. H2O, go to next step. If pressure does not decrease to less than 10 in. H2O, see DIAGNOSTIC AIDS. 5. Disconnect fuel tank vapor and EVAP purge lines from EVAP canister. Plug fuel tank vapor line fitting at EVAP canister. Connect a hand vacuum pump to EVAP purge line fitting at EVAP canister. Ensure EVAP vent solenoid is still commanded ON (closed). Attempt to apply 5 in. Hg to EVAP canister. If vacuum is maintained as specified, go to step 10. If vacuum cannot be maintained as specified, go to next step. 6. Leave system connected as in previous step. Disconnect and plug vent hose at vent valve. Using a hand-held vacuum pump, apply 5 in. Hg. If vacuum can be obtained and held, go to step 8. If vacuum cannot be obtained or held, go to next step. 7. Check vent hose for leak. Repair as necessary. After repairs, go to step 12. If hose is okay, go to step 9. 8. Replace EVAP vent valve. After replacing vent valve, go to step 12. 9. Replace EVAP canister. After replacing canister, go to step 12. 10. Check for missing or faulty fuel cap. Check for disconnected or leaking fuel tank vapor line.

10/29/2009

Diagnostic Aids
Check following items: For missing or damaged " O" rings at EVAP canister fuel vapor and purge line fittings. For cracks or punctures in EVAP canister. For damaged or disconnected source vacuum line, EVAP purge line, vacuum line, EVAP purge line, vent hose or fuel tank vapor line. For faulty connections at VCM. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection. For damaged harness. Inspect wiring harness to EVAP vent solenoid, EVAP purge solenoid, and fuel tank pressure sensor for intermittent open or short.





Page 2 of 2
Check for disconnected or damaged EVAP purge line. Repair as necessary. After repairs, go to step 12. If no problem is found, go to next step. 11. Using scan tool, command EVAP vent solenoid on (closed). With EVAP pressure/purge diagnostic station connected to EVAP service port, attempt to pressurize EVAP system to 15 in. H2O by leaving EVAP pressure/purge diagnostic station control knob in PRESSURIZE position. Using Ultrasonic Leak Detector (J-41413), locate and repair EVAP system leak. It may be necessary to lower fuel tank to check connections at top of tank. After repairs, go to next step. 12. Turn ignition on, engine off. Using scan tool, command EVAP vent solenoid on (closed). Using EVAP pressure/purge diagnostic station, pressurize EVAP system to 15 in. H2O. Monitor diagnostic station pressure gauge. Turn the diagnostic station rotary switch to HOLD position. If pressure decreases to less than 10 in H2O within 2 minutes, repeat step 2. If pressure does not decrease as specified, go to next step. 13. Using scan tool, select DTC, CLEAR INFO function. Using scan tool, perform SERVICE BAY TEST for EVAP system. After performing test, go to next step. 14. Using scan tool, select Read and Record INFO, REVIEW INFO function. If any undiagnosed DTCs are displayed, diagnose affected DTCs. If no DTCs are displayed, system is okay.
For missing or damaged " O" rings at EVAP canister fuel vapor and purge line fittings. For cracks or punctures in EVAP canister. For damaged or disconnected source vacuum line, EVAP purge line, vacuum line, EVAP purge line, vent hose or fuel tank vapor line. For faulty connections at VCM. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection. For damaged harness. Inspect wiring harness to EVAP vent solenoid, EVAP purge solenoid, and fuel tank pressure sensor for intermittent open or short.
10/29/2009

Merlin2021
Oct 29, 2009.


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