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Home >> Jeep >> 1996 >> Cherokee Classic, Part Time, Standard >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Tests W/Codes - 4.0L >> Diagnostic Trouble Code (DTC) Identification >> Test TC-39A - No Change In Map From Start To Run

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

NOTE: For connector terminal identification, refer to CONNECTOR IDENTIFICATION . For wiring diagram, see WIRING DIAGRAMS article in this section.
  1. Turn ign on with engine off. Read DTCs with scan tool. If scan tool displays MAP SENSOR VOLTAGE TOO LOW, perform TEST TC-36A . If scan tool does not display MAP SENSOR VOLTAGE TOO LOW, go to next step.
  2. Using scan tool, clear DTCs. Start engine and allow it to idle for 30 seconds. Using scan tool, read DTCs. If scan tool displays NO CHANGE IN MAP FROM START TO RUN, go to step 8). If scan tool does not display 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 and read MAP sensor voltage while wiggling wiring harness and connectors from PCM to MAP sensor. If engine stalls or voltage becomes erratic while wiggling wiring harness, repair wiring harness and connectors as necessary and perform TEST VER-2A . If engine does not stall and voltage does not become erratic while wiggling wiring harness, go to next step.
  4. While monitoring engine vacuum on scan tool display, snap throttle open and closed several times. If scan tool displays rapid vacuum decrease to less than one in. Hg, go to next step. If vacuum does not decrease rapidly to less than one in. Hg, go to step 7).
  5. Condition required to set DTC is not present at this time. NO CHANGE IN MAP FROM START TO RUN DTC sets if Powertrain Control Module (PCM) detects too small a difference between barometric pressure at ignition and manifold vacuum with engine running for 1.72 seconds. Possible causes are: restricted or leaking vacuum supply to MAP sensor, defective MAP sensor wiring or connector, defective MAP sensor or PCM.
  6. Inspect all related wiring and connectors. Repair wiring and connectors as necessary and perform TEST VER-2A. If wiring and connectors are okay, see INACTIVE DTC CONDITION . Test is complete. Perform TEST VER-2A.
  7. Remove MAP sensor. Inspect intake manifold, throttle and MAP sensor vacuum ports for vacuum restriction. If restriction exists, repair as necessary and perform TEST VER-2A . If no restriction exists, replace MAP sensor and perform TEST VER-2A.
  8. Turn ignition on with engine off. Remove MAP sensor. Inspect intake manifold, throttle and MAP sensor vacuum ports for vacuum restriction. If restriction exists, repair as necessary and perform TEST VER-2A. If no restriction exists, go to next step.
  9. Using scan tool in voltmeter mode, check voltage on MAP sensor connector, 5-volt supply circuit (Violet/White wire). If voltage is 4.5 volts or less, repair open 5-volt supply circuit and perform TEST VER-2A . If voltage is more than 4.5 volts, replace MAP sensor and perform TEST VER-2A.
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