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HOMESERVICE MANUALSGMC1984VALUE VAN P2500, 5.7 M, STANDARD, SM465/M20REPAIR AND DIAGNOSISENGINE PERFORMANCESYSTEMDIESEL CEC TESTINGENGINE SPEED SENSOR CHECK
1984 GMC Value Van P2500, 5.7 M, Standard, SM465/M20

Engine Speed Sensor Check

1984 GMC Value Van P2500, 5.7 M, Standard, SM465/M20SECTION Engine Speed Sensor Check

The sensor is driven by the camshaft. A 5-volt reference signal is provided by the ECM. The ECM measures engine RPM by counting the number of voltage pulses created by the speed sensor (about 4 times per revolution).

NOTE: The following step numbers refer to the numbers in the accompanying flow chart(s).
  1. This step ensures a good 5-volt reference signal. Normally, the ECM should be at about 5 volts for fully charged batteries.
  2. This step checks for proper ECM voltage to the speed sensor. If circuit to ECM is complete, normal voltage should be about 5 volts with harness disconnected at speed sensor.
  3. This checks for good sensor ground circuit (452) from sensor to ECM. Because step 2) indicated an open circuit, this step indicates whether the open is in the wire or at the ECM.
Fig 1: Engine Speed Sensor Check
G9487
RENDER: 1.0x

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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.