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Home >> GMC >> 1991 >> Value Van 7.4 N >> Repair and Diagnosis >> External Pages >> Different car >> Section 35 (Engine Controls - Tests W/Codes - 3.9L) >> Self-Diagnostic Tests >> Test TC-4A - Slow Change In Idle Map Sensor Signal Or No Change In Map From Start To Run (DTC 13)

Test TC-4A - Slow Change In Idle Map Sensor Signal Or No Change In Map From Start To Run (DTC 13)

WARNING: This page is about a different car, the 1995 Dodge Ram Wagon, 1995 Dodge Ram Van, 1995 Dodge Pickup, 1995 Dodge Dakota, and 1995 Dodge Cab & Chassis. However, it is still accessible from the selected car via links, so may be relevant.
NOTE: For circuit and connector terminal identification, see CONNECTOR IDENTIFICATION . For wiring diagram, see WIRING DIAGRAMS  section at the end of this article.
  1. Turn ignition on with engine off. Using scan tool, read trouble codes. If scan tool displays MAP SENSOR VOLTAGE TOO LOW, go to TEST TC-5A. If scan tool does not display MAP SENSOR VOLTAGE TOO LOW, go to next step.
  2. Using scan tool, erase trouble codes. Start engine. Allow engine to idle for 30 seconds. With engine running, use scan tool to read trouble codes. If scan tool displays NO CHANGE IN MAP FROM START TO RUN or SLOW CHANGE IN IDLE MAP SENSOR SIGNAL, go to step 7).
  3. If scan tool does not display NO CHANGE IN MAP FROM START TO RUN or SLOW CHANGE IN IDLE MAP SENSOR SIGNAL, use scan tool to set engine speed to 1500 RPM. With engine running at 1500 RPM, read Manifold Absolute Pressure (MAP) sensor voltage on scan tool. While monitoring MAP sensor voltage, wiggle MAP sensor connector and wiring harness.
  4. If engine stalls or MAP sensor voltage becomes erratic, inspect all related wiring and connectors. Repair wiring or connectors as necessary. Perform TEST VER-2. If engine does not stall and MAP sensor voltage does not become erratic, snap throttle open and closed while monitoring scan tool.
  5. If engine vacuum rapidly drops to less than one in. Hg, condition required to set trouble code is not present at this time. NO CHANGE IN MAP FROM START TO RUN trouble code sets if too small a difference is seen between barometric pressure at key on and manifold vacuum after engine start. SLOW CHANGE IN IDLE MAP SENSOR SIGNAL trouble code sets if variation in MAP signal is less than .157 volt and engine is at 600-1500 RPM. Possible causes for both these trouble codes are: restricted or leaking vacuum/pressure hose to MAP sensor, ice in MAP sensor or passage, MAP sensor failure or failed PCM. Perform TEST VER-2.
  6. If engine vacuum does not rapidly drop to less than one in. Hg, remove MAP sensor. Inspect MAP sensor vacuum port and vacuum connector. If restriction exists, repair as necessary. Perform TEST VER-2. If restriction does not exist, replace MAP sensor. Perform TEST VER-2.
  7. Turn ignition off. Tee a vacuum gauge into Manifold Absolute Pressure (MAP) sensor vacuum hose. Start engine. With engine at idle, read vacuum gauge. If reading is zero in. Hg at idle, repair leak in vacuum hose to MAP sensor. Perform TEST VER-2. If reading is not zero in. Hg, snap throttle open and closed while monitoring scan tool.
  8. If engine vacuum does not rapidly drop, repair restricted vacuum hose. Perform TEST VER-2. If engine vacuum drops rapidly, turn ignition off. Disconnect MAP sensor connector. Turn ignition on. Using scan tool in voltmeter mode, check voltage on MAP sensor connector, 5-volt sensor feed circuit (Violet/White wire). If voltage is less than 4 volts, repair open Violet/White wire. Perform TEST VER-2. If voltage is more than 4 volts, replace MAP sensor. Perform TEST VER-2.
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