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Test TC-39A - No Change In Map Sensor From Start To Run

NOTE: For connector terminal ID, see the CONNECTOR IDENTIFICATION DIRECTORY. For wiring diagram, see WIRING DIAGRAMS - 3.8L article.
  1. Turn ignition on with engine off. Using scan tool, check for stored Diagnostic Trouble Codes (DTCs). If DTC is set to indicate MAP SENSOR VOLTAGE IS TOO LOW, perform TEST TC-36A. If no DTC is set to indicate MAP SENSOR VOLTAGE IS TOO LOW, go to next step.
  2. Using scan tool, clear DTCs from Powertrain Control Module (PCM). Start engine and allow engine to idle for 30 seconds. Using scan tool, check for stored DTCs. If DTC is set to indicate NO CHANGE IN MAP FROM START TO RUN, go to step 9). If no DTC is set to indicate NO CHANGE IN MAP FROM START TO RUN, go to next step.
  3. With engine idling, use scan tool to increase engine speed to 1500 RPM. Note location of MAP sensor. See MAP SENSOR LOCATIONS table.
    MAP SENSOR LOCATIONS

    Application (1) Location
    3.8L On End Of Intake Manifold, Near Throttle Body
    (1) MAP sensor contains a 3-pin connector.
  4. Using scan tool, read MAP sensor voltage with engine at 1500 RPM while wiggling wiring harness and connector from PCM to the MAP sensor. The PCM is located between driver's side front fender and power distribution center, near battery.
  5. If engine stalls or MAP sensor voltage becomes erratic while wiggling wiring harness, repair wiring harness and connector as necessary. Perform TEST VER-2A. If engine does not stall or MAP sensor voltage does not becomes erratic while wiggling wiring harness, go to next step.
  6. While monitoring MAP sensor vacuum display on scan tool, open and close the throttle several times. If MAP sensor vacuum decreases rapidly to less than one in. Hg, go to next step. If MAP sensor vacuum does not decrease rapidly to less than one in. Hg, go to step 8).
  7. Conditions required to set DTC are not present at this time. The MAP sensor measures manifold vacuum and ambient barometric pressure. MAP sensor provides a low voltage signal (.5-1.8 volts) to PCM at idle with high vacuum, and a high voltage signal (3.9-4.8 volts) to PCM at open throttle with low vacuum. DTC may be stored in PCM when too small a difference is seen between barometric pressure at ignition and manifold vacuum. Possible causes are: restricted or leaking vacuum supply to MAP sensor, ice in MAP sensor passages, defective MAP sensor, defective PCM, defective connector terminals or wiring.
  8. Remove MAP sensor. Inspect intake manifold and MAP sensor vacuum ports for vacuum restriction. If restriction exists, repair as necessary. Perform TEST VER-2A. If no restriction exists, replace MAP sensor. Perform TEST VER-2A.
  9. Turn ignition on with engine off. Note location of MAP sensor. See MAP SENSOR LOCATIONS table in this test. Remove MAP sensor and inspect for vacuum restrictions. If vacuum restriction exists, repair as necessary. Reinstall MAP sensor. Perform TEST VER-2A. If no restriction exists, go to next step.
  10. Using voltmeter, check voltage at Violet/White wire on connector for MAP sensor. If voltage is more than 4 volts, replace MAP sensor. Perform TEST VER-2A. If voltage is 4 volts or less, repair open circuit in Violet/White wire between PCM and MAP sensor. Perform TEST VER-2A. The PCM is located between driver's side front fender and power distribution center, near battery.
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