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Engine Sensors & Switches

NOTE: For additional sensor testing specifications, see appropriate SENSOR OPERATING RANGE CHARTS article.

Manufacturer does not provide testing procedures for many individual systems and components. For sensor and switch testing not listed, perform related DTC testing procedure. See appropriate SELF-DIAGNOSTICS article.

  1. Engine Coolant Temperature (ECT) Sensor

    A malfunction in ECT sensor circuit can set a related Diagnostic Trouble Code (DTC). For testing procedure, see appropriate SELF-DIAGNOSTICS article. An out-of-calibration ECT sensor may not set a DTC. Use the following procedure to test sensor calibration.

    Disconnect ECT sensor harness connector. Using an ohmmeter, measure resistance of ECT sensor at specified temperatures. See ECT SENSOR RESISTANCE VALUES  table. Resistance should be high when engine is cold and drop as engine warms. With vehicle sitting overnight, IAT sensor and ECT sensor should have close to the same resistance reading. If resistance is not within specification, replace ECT sensor.

    ECT SENSOR RESISTANCE VALUES

    Temperature °F (°C) Ohms
    212 (100) 177
    158 (70) 467
    104 (40) 1459
    68 (20) 3520
    32 (0) 9420
    5 (-15) 21,450
    -40 (-40) 100,700
    2. NOTE: Intake Air Temperature (IAT) sensor may also be referred to as Manifold Air Temperature (MAT) sensor.

  2. Intake Air Temperature (IAT) Sensor
    A malfunction in IAT sensor circuit can set a related Diagnostic Trouble Code (DTC). For testing procedure, see appropriate SELF-DIAGNOSTICS article. An out-of-calibration IAT sensor may not set a DTC. Use the following procedure to test sensor calibration.

    Disconnect IAT sensor harness connector. Using an ohmmeter, measure resistance of IAT sensor at specified temperatures. See IAT SENSOR RESISTANCE VALUES  table. Resistance should be high when air temperature is cold and drop as air temperature warms. With vehicle sitting overnight, ECT sensor and IAT sensor should have close to the same resistance reading. If resistance is not within specification, replace IAT sensor.

    IAT SENSOR RESISTANCE VALUES

    Temperature °F (°C) Ohms
    212 (100) 177
    158 (70) 467
    104 (40) 1459
    68 (20) 3520
    32 (0) 9420
    5 (-15) 21,450
    -40 (-40) 100,700
NOTE: MAP sensor circuit diagnosis is only available from manufacturer for 2.2L and 3.4L engines.

  1. MAP Sensor Circuit Diagnosis (2.2L)

    If On-Board Diagnostic (OBD) system check has been performed, go to next step. If On-Board Diagnostic (OBD) system check has not been performed, perform On-Board Diagnostic (OBD) system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK in appropriate SELF-DIAGNOSTICS article.
  2. Install scan tool and retrieve DTCs. If no MAP sensor related DTCs are set, go to next step. If any MAP sensor related DTCs are set, perform appropriate DTC test. See appropriate SELF-DIAGNOSTICS article.
  3. Turn ignition on with engine off. Compare MAP sensor reading with that of a known-good vehicle. If voltage readings are within 0.4 volt of each other, go to next step. If voltage readings are not within 0.4 volt of each other, go to step  5.
  4. Disconnect and plug vacuum source to MAP sensor. Connect a hand-held vacuum pump to vacuum source port on MAP sensor. Apply 10 in. Hg of vacuum to MAP sensor while observing MAP sensor reading on scan tool. Subtract this reading from the reading obtained in step 3)  . If difference is greater than 1.5 volts, go to step  6. If difference is not greater than 1.5 volts, go to step  7.
  5. Replace MAP sensor. After repairs, go to step  9.
  6. Check MAP sensor vacuum source for leakage or restriction, and that vacuum source only supplies MAP sensor. If problem exists, go to step  8. If problem does not exist, go to step  9.
  7. Check for poor connection at MAP sensor. If poor connection does not exist, go to step  5. If poor connection exists, repair as necessary and go to step  9.
  8. Repair leak or restriction in MAP sensor vacuum source as necessary. After repairs, go to next step.
  9. Operate vehicle under conditions which original symptom was noted. If system operates properly, system is okay at this time. If system does not operate properly, go to step  2.

  1. MAP Sensor Circuit Diagnosis (3.4L)

    If On-Board Diagnostic (OBD) system check has been performed, go to next step. If On-Board Diagnostic (OBD) system check has not been performed, perform On-Board Diagnostic (OBD) system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK in appropriate SELF-DIAGNOSTICS article.
  2. Check for the following:
    • Missing or damaged MAP sensor seal.
    • Damage, disconnected or misrouted vacuum hoses.
    • Intake manifold vacuum leaks.
    • Vacuum leaks at throttle body.
    • Vacuum leaks in EGR system.
    • Faulty, missing or incorrectly installed PCV valve.

    If a problem does not exist, go to next step. If a problem exists, repair as necessary and go to step  14.

  3. Disconnect MAP sensor harness connector. Using scan tool, observe MAP sensor parameter. If zero volts is displayed, go to next step. If zero volts is not displayed, go to step  12.
  4. Using a test light connected to battery voltage, probe MAP sensor signal circuit (Light Green wire) at MAP sensor harness connector. See appropriate wiring diagram in WIRING DIAGRAMS article. Observe MAP sensor parameter on scan tool. If 4.95 volts is displayed, go to next step. If 4.95 volts is not displayed, go to step  8.
  5. Using a fused jumper wire, connect MAP sensor signal circuit (Light Green wire) and MAP sensor reference voltage circuit (Gray wire) at MAP sensor harness connector. See appropriate wiring diagram in WIRING DIAGRAMS article. Observe MAP sensor parameter on scan tool. If scan tool displays 4.95 volts, go to next step. If scan tool does not display 4.95 volts, go to step  7.
  6. Turn ignition off. Disconnect PCM harness connectors. Check MAP sensor ground circuit (Orange/Black wire) for open, high resistance or poor connection at PCMs. If problem does not exist, go to step  10. If problem exists, repair as necessary and go to step  14.
  7. Check MAP sensor reference voltage circuit (Gray wire) for open, high resistance or poor connection at PCM. If problem does not exist, go to step  9. If problem exists, repair as necessary and go to step  14.
  8. Turn ignition off. Disconnect PCM harness connectors. Check MAP sensor signal circuit (Light Green wire) for open, high resistance, short to ground or short to sensor. If problem does not exist, go to next step. If problem exists, repair as necessary and go to step  14.
  9. Check MAP sensor signal circuit (Light Green wire) for poor connection at PCM. If problem does not exist, go to step  13. If problem exists, repair as necessary and go to step  14.
  10. Check for poor connection at MAP sensor. If problem does not exist, go to next step. If problem exists, repair as necessary and go to step  14.
  11. Replace MAP sensor. After repairs, go to step  14.
  12. Turn ignition off. Disconnect PCM harness connector. Turn ignition on. Check MAP sensor signal circuit (Light Green) for a short to voltage or short to MAP sensor reference voltage circuit (Gray wire). If problem does not exist, go to next step. If problem exists, repair as necessary and go to step  14.
  13. Replace PCM. Program PCM. Perform VTD password relearn procedure and crankshaft variation learn procedure. See COMPUTER RELEARN PROCEDURES article in GENERAL INFORMATION. After repairs, go to next step.
  14. Start engine and let idle. While observing MAP sensor parameter on scan tool, increase engine RPM. If MAP sensor value changes, system is okay. If MAP sensor value does not change, go to step  2.
    NOTE: Ensure oil is okay before performing engine oil level switch diagnosis.

  1. Engine Oil Level Switch Diagnosis
    If On-Board Diagnostic (OBD) system check has been performed, go to next step. If On-Board Diagnostic (OBD) system check has not been performed, perform On-Board Diagnostic (OBD) system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK in appropriate SELF-DIAGNOSTICS article.
  2. Using scan tool, observe engine oil level display. If scan tool does not display OK, go to next step. If scan tool displays OK, check for poor connections at engine oil level switch and PCM. If poor connection exists, repair as necessary. If poor connection does not exist, perform warning light diagnosis. See PCM CONTROLLED WARNING LIGHTS & GAUGES  under MISCELLANEOUS CONTROLS.
  3. Turn ignition off. Disconnect PCM harness connectors. Using a test light connected to battery voltage, probe engine oil level switch signal circuit (Brown wire) at PCM harness connector. If test light does not illuminate, go to next step. If test light illuminates, go to step  7.
  4. Ensure ignition is off. Reconnect PCM harness connectors. Turn ignition on. Raise and support vehicle. Disconnect engine oil level switch harness connector. Using DVOM, measure voltage between engine oil level switch harness connector terminals. If battery voltage does not exist, go to next step. If battery voltage exists, go to step  8.
  5. Using DVOM, measure voltage between chassis ground and engine oil level switch signal circuit (Brown wire) at engine oil level switch harness connector. If battery voltage does not exist, go to next step. If battery voltage exists, go to step  9.
  6. Check for open in engine oil level switch signal circuit (Brown wire) between engine oil level switch and PCM. If open exists, repair as necessary and go to step  12. If open does not exist, check for poor connections at engine oil level switch and PCM. If poor connection exists, repair as necessary. If poor connection does not exist, perform warning light diagnosis. See PCM CONTROLLED WARNING LIGHTS & GAUGES  under MISCELLANEOUS CONTROLS.
  7. Check for poor connections at PCM. If poor connection exists, repair as necessary and go to step  12. If poor connection does not exist, go to step  11.
  8. Check for poor connections at engine oil level switch. If poor connection exists, repair as necessary and go to step  12. If poor connection does not exist, go to step  10.
  9. Locate and repair open in engine oil level switch ground circuit (Black/White wire). After repairs, go to step  12.
  10. Replace engine oil level switch. After repairs, go to step  12.
  11. Replace PCM. Program PCM. Perform VTD password relearn procedure and crankshaft variation learn procedure. See COMPUTER RELEARN PROCEDURES article in GENERAL INFORMATION. After repairs, go to next step.
  12. Start engine and allow to warm to normal operating temperature. Turn ignition off. Allow engine to cool for 15 minutes. Turn ignition on. Using scan tool, observe engine oil level display. If scan tool displays OK, system is okay. If scan tool does not display OK, go to step  3.
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