GM Full-Size Trucks 1988-1998 Repair Information

Component Testing

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Vehicle Speed Sensor

Prefer to Driveability & Emissions Controls of this repair guide for VSS testing.

Wheel Speed Sensor

See Figure 1

  1. Elevate and safely support the vehicle.
  2.  
  3. Unplug the sensor electrical connection.
  4.  
  5. Check the condition of the sensor terminals and the wiring harness terminals. Repair as necessary.
  6.  
  7. Check the sensor wiring harness for an open or short circuit. Repair as necessary.
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  9. Using a Digital Volt OhmMeter (DVOM) set to read resistance, probe the sensor terminals.
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  11. If the resistance is not as specified in the accompanying charts, the sensor may be defective.
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  13. Turn the DVOM to the A/C voltage scale and spin the wheel, there should be a voltage reading. As the wheel speed increases, the voltage should increase. If there is no voltage present, or the voltage does not increase with wheel speed, check the tone wheel for defects. If the tone wheel is found to be in good condition, replace the sensor.
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Fig. Fig. 1: Wheel speed sensor temperature versus resistance chart

Pump motor circuit

  1. Check the condition of the fuse in the relay center and replace as necessary.
  2.  
  3. Unplug the pump motor electrical connection.
  4.  
  5. Check the condition of the terminals and the wiring harness terminals. Repair as necessary.
  6.  
  7. Attach the electrical connection.
  8.  
  9. Using a Digital Volt OhmMeter (DVOM) set to read voltage, backprobe between the black (ground) wire and red (power) wire terminals of the harness . The voltage should be between 9-14 volts.
  10.  
  11. If the voltage is less than 9 volts, set the DVOM on the lowest resistance scale, disconnect the harness and the positive and negative battery terminals. Connect one probe to the positive battery cable and the other probe to red wire terminal. Note the reading. Connect one probe to the negative battery cable and the other probe to black wire terminal. Note the reading.
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  13. If the resistance is less than one ohm the wiring is fine and the control unit should be replaced.
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  15. If the resistance is more than one ohm, clean and tighten the terminals or repair the wiring as needed.
  16.  
  17. Attach all unplugged wires and recheck the voltage.
  18.  
  19. Clear the trouble codes and road test the vehicle. If the trouble code returns, check the motor supply voltage again.
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  21. If the voltage is now between 9-14 volts and the pump is still not functioning properly, replace the assembly.
  22.  
  23. If the voltage is still lower than 9 volts, there may be a problem with the EBCM.
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