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 DIAGNOSIS (SINGLE PAGE)ELECTRICALGAUGESINSTRUMENT PANEL - ANALOG - G SERIESSYSTEM TESTSOIL PRESSURE ALWAYS INDICATES HIGH
1999 GMC Forward Control 5.7 R, Automatic
Oil Pressure Always Indicates High
1999 GMC Forward Control 5.7 R, AutomaticSECTION Oil Pressure Always Indicates High
- With engine running, compare oil pressure with oil pressure gauge reading. If readings are reasonably accurate, gauge is operating properly. Check engine. If readings are not reasonably accurate. go to next step.
- Disconnect oil pressure sender harness connector. Connect a fused jumper wire between ground and Tan wire terminal at oil pressure sender harness connector. Oil pressure gauge should indicate 0 psi. If indicator indicates 0 psi, replace oil pressure sender. If indicator indicates high oil pressure, go to next step.
- Disconnect instrument cluster harness connector. Connect a self-powered test light between instrument cluster harness connector terminal B8 (Tan wire) and oil pressure sender Tan wire terminal. If test light lights, replace instrument cluster. See INSTRUMENT CLUSTER under REMOVAL & INSTALLATION. If test light does not light, repair open in Tan wire.
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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.