Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSGMC1999FORWARD CONTROL 5.7 R, AUTOMATICREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 86 (ENGINE CONTROLS - SELF-DIAGNOSTICS - 3.0L)DIAGNOSTIC TESTSDTC P0442: EVAP SYSTEM - SMALL LEAK DETECTEDDIAGNOSTIC PROCEDURES
1999 GMC Forward Control 5.7 R, Automatic
Diagnostic Procedures
1999 GMC Forward Control 5.7 R, AutomaticSECTION Diagnostic Procedures
WARNING: This page is about a different car, the 2002 Saturn Vue. However, it is still accessible from the selected car via links, so may be relevant.
NOTE:
If DTC P0440, P0442, P0446 or P0496 is set, EVAP special functions on scan tool will not be allowed. Clear DTCs before performing these tests.
- Turn ignition on, engine off. Remove fuel cap. Using scan tool, monitor fuel tank pressure sensor. If voltage is 1.4-1.6 volts, go to next step. If voltage is less than 0.2 volt, see DTC P0452: EVAP FUEL TANK PRESSURE SENSOR CIRCUIT - LOW VOLTAGE . If voltage is 0.20-1.40 volts or 1.60-4.75 volts, replace FTP sensor. If voltage is more than 4.75 volts, see DTC P0453: EVAP FUEL TANK PRESSURE SENSOR CIRCUIT - HIGH VOLTAGE .
- Install fuel cap. Clear ECM DTCs. Using scan tool, seal EVAP system by using EVAP PURGE/SEAL special function. Connect EVAP System Tester (J41750-A) to EVAP service port. Perform diagnostic process as described on EVAP system tester to locate a small leak. If leak was identified, repair leak. Perform flowmaster test as described on EVAP system tester to verify fix, or run EVAP service bay test. If leak was not identified, see DIAGNOSTIC AIDS .
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.