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 101 (SUPPLEMENTAL INFLATABLE RESTRAINT SYSTEM)DIAGNOSTIC TESTSDTC B0035: DISCRIMINATING SENSOR CLOSED OR SHORT TO GROUNDDIAGNOSTIC PROCEDURE

1999 GMC Forward Control 5.7 R, Automatic

Diagnostic Procedure

1999 GMC Forward Control 5.7 R, AutomaticSECTION Diagnostic Procedure

WARNING: This page is about a different car, the 2002 GMC Savana and 2002 Chevrolet Chevy Express. However, it is still accessible from the selected car via links, so may be relevant.

If SIR Diagnostic System Check has been performed, go to next step. If SIR Diagnostic System Check has not been performed, go to SIR DIAGNOSTIC SYSTEM CHECK .
Turn ignition off. Disconnect front end discriminating sensor in-line connector, located next to under hood fuse-relay box. See Fig 1. Inspect both sides of connector for corrosion, poor connections or damage. If either half of connector is damaged, replace applicable connector. See WIRE REPAIR . Go to step 8. If both sides of connector are okay, go to next step.
Disconnect front end discriminating sensor connector. See FRONT END DISCRIMINATING SENSOR under REMOVAL & INSTALLATION. If harness side of connector shows signs of corrosion, poor connections or damage, replace connector. See WIRE REPAIR . Go to step 8. If front end discriminating sensor side of connector is damaged, replace front end discriminating sensor. Go to step 8. If connector is okay, go to next step.
Disconnect SDM harness connector. If connector shows signs of corrosion, poor connections or damage, replace connector. See WIRE REPAIR . Go to step 8. If SDM harness connector is okay, go to next step.
NOTE: Use Digital Multimeter (J-39200) and Connector Test Adapter Kit (J-35616-A) or Flat Wire Probe Adapter Kit (J-42675) when performing electrical tests.
Measure resistance between front end discriminating sensor terminals "A" and "B". See Figure. If resistance is more than 950 ohms, go to step 7. If resistance is 950 ohms or less, go to next step.
Measure resistance of between front end discriminating sensor signal circuit and ground. If resistance is infinite, go to next step. If resistance is not infinite, repair short to ground. Go to step 8.
Replace front end discriminating sensor. Go to next step.
Reconnect all SIR components. Ensure all components are properly mounted. Using scan tool, clear all SIR DTC's. Road test vehicle. If DTC resets, go to step 2. If DTC does not reset, system is normal.

Fig 1: Identifying Front End Discriminating Sensor In-line Connector

Courtesy of GENERAL MOTORS CORP.

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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.