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Servo Test

  1. Turn the ignition on. Disconnect connector from control module assembly. With an ohmmeter, probe between connector cavity pins F (circuit No. 398) and H (circuit No. 399). Check for resistance of 15-25 ohms.
  2. If resistance in step 1) is incorrect, disconnect electrical connector from servo. With an ohmmeter, probe between pins B (circuit No. 399) and D (circuit No. 398) on the servo assembly.
  3. If resistance in step 2) is 15-25 ohms, check circuits No. 399 and 398 (pin H of control module to pin D of servo, and pin F of control module to pin B of servo). If resistance in step 2) is not 15-25 ohms, replace servo.
  4. If resistance in step 1) is correct, turn off ignition. Disconnect connectors from control module and servo assemblies. With ohmmeter, probe between connector pin cavity C (circuit No. 403) and ground. Measure resistance of wire.
  5. If continuity is indicated in step 4), find short to ground and repair (circuit No. 403). If no continuity is indicated, leave ohmmeter connected. Use jumper wire to connect cavity A of servo to ground. Measure resistance.
  6. If resistance measures zero ohms, go to step 7). If resistance does not measure zero ohms, find open in circuit No. 403 (pin C of control module to pin A of connector). Repair or replace as necessary.
  7. If resistance in step 5) measured zero ohms, remove jumper wire and with ohmmeter connected between control module connector cavity pin K and ground, check for continuity.
  8. If continuity is indicated in step 7), find short to ground and repair. If no continuity is indicated, leave ohmmeter connected and use a jumper wire to connect cavity E of servo connector to ground. Measure resistance.
  9. If the resistance is zero ohms, go to step 10). If resistance is not zero ohms, find open in circuit No. 402 (pin K of control module to pin E of servo). Repair or replace as necessary.
  10. Turn the ignition off. Disconnect connector from servo. Probe connector cavity pin C (circuit No. 150) to ground. Measure resistance. If resistance is zero ohms, go to step 13). If resistance is not zero ohms, disconnect electrical connector from control module.
  11. With ohmmeter, probe connector cavity J (circuit No. 150) to ground. If the resistance is not zero ohms, find open in circuit No. 150 (pin J of control module to ground point). Repair or replace as necessary.
  12. If resistance in step 11) was zero ohms, find open in circuit No. 150 (pin C of servo to splice). Repair or replace as necessary.
  13. If resistance in step 10) was zero ohms, disconnect linkage, chain or cable to throttle. Make sure the electrical connector to the servo is still disconnected. Start the engine and let idle.
  14. Manually actuate the servo vent and vacuum control valves by connecting jumper wires from positive battery terminal to pins A and E on the servo assembly. With another jumper wire, connect one end to pin C on servo and the other end to a known good ground.
  15. With brake (and clutch) pedal in free position, check to see if servo pulls in full stroke. If not, go to step 18). If yes, remove jumper wire from pin E on the servo. If servo stays at full stroke, check for proper operation of electrical connector at servo.
  16. If servo does not stay at full stroke position in step 15), remove the larger of the hoses to servo and plug orifice on servo. Reconnect the jumper wire to pin E until servo pulls in full stroke. Remove jumper wire from pin E.
  17. If servo does not stay at full stroke position, replace servo. If it does stay, check brake and/or clutch release valve adjustment. Check valves and hoses for leaks. Repair or replace as required.
  18. If servo did not pull in full stroke in step 15), remove the larger hose from the servo and plug the orifice. Check servo operation. If servo pulls in full stroke, check brake and/or clutch release valve for adjustment. Check for leaks in hose.
  19. If servo did not pull in full stroke, remove smaller vacuum hose from servo and check for vacuum. If vacuum is present, inspect connectors carefully for leaks. If okay, replace servo. If vacuum is not present, check connections between servo and vacuum source for leaks or incorrect connections.
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