SYS.OK|MANUAL.DB● LIVE
HOMESERVICE MANUALSGMC1999FORWARD CONTROL 5.7 R, AUTOMATICREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 79 (ENGINE CONTROL SYSTEM SELF-DIAGNOSTICS - 3.4L)DIAGNOSTIC TESTSDTC P1635: 5-VOLT REFERENCE LOWDIAGNOSTIC 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 Pontiac Grand Am, 2002 Oldsmobile Alero, 2002 Chevrolet Monte Carlo, and 2002 Chevrolet Impala. However, it is still accessible from the selected car via links, so may be relevant.
  1. Perform diagnostic system check - engine controls. See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS  under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
  2. Observe the Freeze Frame/Failure Records data for this DTC. Turn ignition off for 30 seconds. Start the engine. Operate the vehicle within the Conditions for Running the DTC or as close to the Freeze Frame/Failure Records data that you observed. See CONDITIONS FOR RUNNING DTC . Does the DTC fail this ignition? If yes, go to next step. If no, go to INTERMITTENT CONDITIONS  under SELF-DIAGNOSTIC SYSTEM.
  3. Inspect the PCM and engine grounds. Ensure that the grounds are clean and secure. If a problem is found, repair as necessary. Did you find and correct the condition? If yes, go to step  13. If no, go to next step.
  4. Turn ignition off. Disconnect the EGR valve electrical connector. Turn ignition on, with engine off. Using a Digital Multimeter (DMM), measure voltage between the 5-volt reference circuit and engine ground. Does the voltage measure about 5 volts? If yes, go to step  6. If no, go to next step.
  5. Does the voltage measure more than 5 volts? If yes, go to step  9. If no, go to step  7.
  6. Reconnect EGR valve. Disconnect TP sensor harness connector. Using a DMM, measure voltage between the TP sensor harness connector 5-volt reference 1 circuit and engine ground. Does the voltage measure about 5 volts? If yes, see INTERMITTENT CONDITIONS  under SELF-DIAGNOSTIC SYSTEM. If no, go to step  10.
  7. Monitor Digital Multimeter (DMM) while disconnecting all other devices connected to 5-volt reference circuit one at a time. If voltage changes when one of the components are disconnected, replace the component. Was a component replaced? If yes, go to step  13. If no, go to next step.
  8. Turn ignition off. Disconnect the PCM. Inspect the 5-volt reference circuit for a short to ground or any sensor low reference circuit. If a problem is found, repair as necessary. Did you find and correct the condition? If yes, go to step  13. If no, go to step  12.
  9. Turn ignition off. Disconnect the PCM. Turn ignition on, with engine off. Inspect the following circuits for a short to voltage: The 5-volt reference circuit, MAP sensor signal circuit, or FTP sensor signal circuit. If a problem is found, repair as necessary. Did you find and correct the condition? If yes, go to step  13. If no, go to step  12.
  10. Inspect for a short between the EGR control high circuit and the 5-volt reference circuit and repair as necessary. Did you find and correct the condition? If yes, go to step  13. If no, go to next step.
  11. Replace the EGR valve. After repairs, go to step
  12. Replace PCM. Perform PCM relearn procedure. See POWERTRAIN CONTROL MODULE  under PROGRAMMING. After replacing PCM, go to next step.
  13. Use the scan tool in order to clear the DTCs. Turn ignition off for 30 seconds. Start the engine. Operate the vehicle within the Conditions for Running the DTC. See CONDITIONS FOR RUNNING DTC . Does the DTC run and pass? If yes, go to next step. If no, go to step  2.
  14. Using scan tool, observe stored information and Capture Info. Does the scan tool display any DTCs that you have not diagnosed? If yes, see DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no, system is okay.
RENDER: 1.0x

NO RELATED

Recommended Tools & Savings

Use the Manual With the Right Hardware

Pair factory procedures with proven DIY tools so the instructions are easier to execute.

Affiliate disclosure: We may earn a commission at no extra cost to you.

Shop Manual-Ready ToolsFree Quote CheckQuote Shield Pro

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.