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 26 (THEFT DETERRENT SYSTEM)DIAGNOSTIC TESTSDTC P1626: INVALID FUEL ENABLE PASSWORDTESTING
1999 GMC Forward Control 5.7 R, Automatic
DTC P1626: Invalid Fuel Enable Password: Testing
1999 GMC Forward Control 5.7 R, AutomaticSECTION Testing
WARNING: This page is about a different car, the 2002 GMC Savana, 2002 Chevrolet Chevy Express, 2001 GMC Savana, and 2001 Chevrolet Chevy Express. However, it is still accessible from the selected car via links, so may be relevant.
- If theft deterrent diagnostic system check has been performed, go to next step. If theft deterrent diagnostic system check has not been performed, go to THEFT DETERRENT DIAGNOSTIC SYSTEM CHECK .
- Turn ignition switch to OFF position. Connect scan tool to Data Link Connector (DLC), located below steering column. See Figure . Momentarily turn ignition switch to CRANK position, not letting engine start, release ignition switch to RUN position. Select scan tool PCM display DTCs function. If scan tool displays DTC P1626 as a current DTC, go to next step. If scan tool does not display DTC P1626 as a current DTC, check for intermittent or poor connections. See DIAGNOSTIC AIDS .
- Check for open, short to ground or short to voltage in Purple wire between Passlock(tm) module harness connector terminal B4, DLC terminal No. 2, and PCM harness connector C1 terminal No. 59. See Figure , Fig 1 and Fig 2 . Check for loose or damaged terminals at Passlock(tm) module, PCM or DLC connectors. If Purple wire and connections are okay, go to next step. If Purple wire or connections are not okay, go to step 6 .
NOTE:
Diagnose Bxxxx codes prior to diagnosing any Pxxxx code.
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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.