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Home >> Jeep >> 1996 >> Grand Cherokee Limited, 5.2 Y >> Repair and Diagnosis >> External Pages >> Different car >> Section 180 (Engine Controls - Tests W/Codes - 4.0L) >> Self-Diagnostic Tests >> Test TC-18A - Idle Air Control Motor Circuits (DTC 25)

Test TC-18A - Idle Air Control Motor Circuits (DTC 25)

WARNING: This page is about a different car, the 1995 Jeep Wrangler, 1995 Jeep Grand Cherokee, and 1995 Jeep Cherokee. However, it is still accessible from the selected car via links, so may be relevant.
NOTE: Perform TEST TC-1A  before proceeding with this test. For connector terminal identification, see CONNECTOR IDENTIFICATION  at beginning of article. For wiring diagrams, see WIRING DIAGRAMS  at the end of this article. Perform TEST VER-2A  after each repair.
  1. Using scan tool, erase trouble code messages. Using scan tool, actuate Idle Air Control (IAC) motor and read trouble code messages. If scan tool does not display IDLE AIR CONTROL MOTOR CIRCUITS, go to next step. If scan tool displays IDLE AIR CONTROL MOTOR CIRCUITS, go to step 5).
  2. Condition required to set trouble code is not present at this time. IDLE AIR CONTROL MOTOR CIRCUITS trouble code sets if any of 4 IAC motor driver circuits are shorted to ground or battery voltage for 2.75 seconds during IAC motor activation. Possible causes are: driver motor circuits shorted to ground, battery voltage or each other, shorted IAC motor, PCM failure or IAC motor connector terminals or wires defective. PCM cannot detect an open driver circuit or a stuck IAC motor. Inspect all related wiring and connectors and repair as necessary. If no problems were found with wiring and connectors, go to next step.
  3. Start engine and allow to idle. When engine reaches normal operating temperature, use scan tool to actuate IAC wiggle test. If idle speed raises and lowers with display, go to next step. If idle speed does not raise and lower with display, go to TEST NTC-9A  .
  4. With scan tool actuating IAC wiggle test, wiggle connectors and wiring harness between IAC motor and PCM. If IAC motor stops operating, repair connectors and/or harness as necessary. If IAC motor does not stop operating, stop IAC wiggle test and see INACTIVE DTC CONDITION  in this article. Test is complete.
  5. Turn ignition off. Disconnect Idle Air Control (IAC) 4-pin connector and ensure connector is clean and not damaged. Turn ignition on, engine off. Using scan tool, erase trouble codes. Using scan tool actuate IAC motor and read trouble codes. If scan tool displays, IDLE AIR CONTROL MOTOR CIRCUIT, go to next step. If scan tool does not display, IDLE AIR CONTROL MOTOR CIRCUIT, replace IAC motor.
  6. Using scan tool in voltmeter mode, measure voltage of IAC No. 1 driver circuit at IAC connector. See appropriate PCM/IAC TERMINAL IDENTIFICATION table. Voltage may switch or remain constant. If voltage is more than 10 volts at any time, go to next step. If voltage is not more than 10 volts at any time, go to TEST TC-18B  .
  7. Using scan tool in voltmeter mode, check voltage of IAC No. 2 driver circuit at IAC motor connector. See appropriate PCM/IAC TERMINAL IDENTIFICATION table. Voltage may switch or remain constant. If voltage is more than 10 volts at any time, go to next step. If voltage is not more than 10 volts at any time, go to TEST TC-18C  .
  8. Using scan tool in voltmeter mode, check voltage of IAC No. 3 driver circuit at IAC motor connector. See appropriate PCM/IAC TERMINAL IDENTIFICATION table. Voltage may switch or remain constant. If voltage is more than 10 volts at any time, go to next step. If voltage is not more than 10 volts at any time, go to TEST TC-18D  .
  9. Using scan tool in voltmeter mode, check voltage of IAC No. 4 driver circuit at IAC motor connector. See appropriate PCM/IAC TERMINAL IDENTIFICATION table. Voltage may switch or remain constant. If voltage is more than 10 volts at any time, go to next step. If voltage is not more than 10 volts at any time, go to TEST TC-18E  .
  10. Turn ignition off. Disconnect Powertrain Control Module (PCM) connector and ensure connector is clean and not damaged. Using an external ohmmeter, measure resistance between IAC No. 1 driver circuit and No. 2, 3 and 4 driver circuits. See appropriate PCM/IAC TERMINAL IDENTIFICATION table. If resistance is more than 5 ohms, go to next step. If resistance is less than 5 ohms on any driver circuits, repair IAC driver circuits that are shorted together.
  11. Using an external ohmmeter, measure resistance between IAC No. 2 driver circuit and No. 3 and 4 driver circuits. See appropriate PCM/IAC TERMINAL IDENTIFICATION table. If resistance is more than 5 ohms, go to next step. If resistance is less than 5 ohms on any driver circuits, repair IAC driver circuits that are shorted together.
  12. Using an external ohmmeter, measure resistance between IAC Nos. 3 and 4 drivers. See appropriate PCM/IAC TERMINAL IDENTIFICATION table. If resistance is less than 5 ohms, repair IAC driver circuits that are shorted together. If resistance is not less than 5 ohms, replace PCM.
PCM/IAC TERMINAL IDENTIFICATION (XJ & YJ BODIES) (1)

Wire Color & (PCM Terminal No.) IAC Driver Circuit No. Connector Terminal No.
Gray/Red (39) 1 1
Brown/White (40) 3 2
Violet/Black (59) 4 3
Yellow/Black (60) 2 4
(1) For connector terminal identification, see CONNECTOR IDENTIFICATION  at beginning of article.
PCM/IAC TERMINAL IDENTIFICATION (ZJ BODY) (1)

Wire Color & (PCM Terminal No.) IAC Driver Circuit No. Connector Terminal No.
Yellow/Black (39) 4 1
Brown/White (40) 2 3
Gray/Red (59) 1 4
Violet/Black (60) 3 2
(1) For connector terminal identification, see CONNECTOR IDENTIFICATION  at beginning of article.
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