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HOMESERVICE MANUALSPLYMOUTH1994COLT VISTA SE, STANDARDREPAIR AND DIAGNOSIS (SINGLE PAGE)ENGINE PERFORMANCESYSTEMENGINE CONTROLS - TESTS W/CODESDIAGNOSTIC TESTSCODE 55: IDLE AIR CONTROL POSITION SENSOR
1994 Plymouth Colt Vista SE, Standard

Code 55: Idle Air Control Position Sensor

1994 Plymouth Colt Vista SE, StandardSECTION Code 55: Idle Air Control Position Sensor
NOTE: For component terminal identification, see TERMINAL IDENTIFICATION  . For wiring diagrams, see WIRING DIAGRAMS article in the ENGINE PERFORMANCE Section.
  1. Manufacturer does not provide component testing procedure without using scan tester. Ensure engine coolant temperature is 185-205°F (85-95°C). Place transmission in Park or Neutral. Turn off all accessories except A/C. Ensure A/C clutch is operating when A/C system is on. Allow engine to idle.
  2. Using scan tester, read Idle Air Control (IAC) position sensor step. See IAC POSITION SENSOR STEP SPECIFICATIONS  table. If scan tester does not read as specified, replace IAC position sensor. If readings are as specified, go to next step.
    IAC POSITION SENSOR STEP SPECIFICATIONS

    A/C Switch Position Standard Step Value
    Off 2-20
    On Increase From 8-50
    (1) Increase From 3-40
    (1) For A/T models. Brakes applied, transmission selector in "D" and A/C on.
  3. Disconnect ECM connector and IAC position sensor connector. Ground specified ECM connector terminal and using DVOM, check continuity between chassis ground and specified IAC connector terminal. See ECM-TO-IAC HARNESS CIRCUIT IDENTIFICATION  table. If continuity does not exist, repair wiring harness as necessary. If continuity exists, go to next step.
    ECM-TO-IAC HARNESS CIRCUIT IDENTIFICATION

    Application ECM Terminal No. IAC Terminal No.
    All Models 13 & 23 1
    67 2
    68 4
  4. With IAC position sensor connector disconnected, check continuity between chassis ground and IAC position sensor connector terminal No. 3. If continuity does not exist, repair wiring harness as necessary. If continuity exists, go to next step.
  5. With IAC position sensor connector disconnected and ECM connector connected, turn ignition switch to ON position. Check for voltage between chassis ground and IAC connector terminals No. 2 and No. 4. If voltage is not 4.8-5.2 volts on either circuit, replace ECM. If voltage is as specified, go to next step.
  6. Check voltage between chassis ground and IAC position sensor connector terminal No. 1. If voltage is not 4.8-5.2 volts, replace ECM. If voltage is as specified, condition required to set code is not present at this time. Test is complete. Intermittent problem may exist. See TESTS W/O CODES article in the ENGINE PERFORMANCE Section.
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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.