DTC P0505: Idle Control System Failure

NOTE: For terminal identification, see TERMINAL IDENTIFICATION . For circuit and wire color identification, see WIRING DIAGRAMS article.

Procedures are provided by manufacturer for component testing using an engine analyzer with oscilloscope capability. Refer to manufacturer's operation manual for instructions in use of oscilloscope. If using engine analyzer, go to step 3). If using scan tool, go to next step.

Using scan tool, read Idle Air Control (IAC) position sensor step (item 45). See IAC POSITION SENSOR STEP SPECIFICATIONS table. If scan tool does not read as specified, replace IAC position sensor. If readings are as specified, go to step 5).

IAC POSITION SENSOR STEP SPECIFICATIONS

A/C Switch Position

Standard Step Value

Off

2-25

Off To On

Increase From 10-70

⁽¹⁾

Increase From 5-50

⁽¹⁾	Brakes applied. A/C Off on Montero. A/C On on 3000GT. Move gear selector lever to Drive position.

NOTE: Check wave pattern when idle speed increases when A/C is turned on. Wave pattern display lasts less than one second.

Disconnect IAC motor connector. Install Test Harness (MB998463) between IAC motor and connector. Using engine analyzer with oscilloscope capability, connect special patterns probe in sequence to test harness terminals No. 1 (Red clip), 3 (Blue clip), 4 (Black clip) and 6 (Yellow clip) or PCM terminals No. 4, 5, 17 and 18 respectively. Start engine and allow it to idle. Turn A/C on. Compare oscilloscope wave pattern with known-good wave pattern. See Fig 1 . Turn engine off. If wave pattern is not normal, go to next step. If wave pattern is normal, fault is intermittent. See INTERMITTENT DTCS .

Fig 1: Identifying Know-Good IAC Motor Wave Pattern
Courtesy of MITSUBISHI MOTOR SALES OF AMERICA
Disconnect IAC motor connector. Leave test harness connected to IAC motor. Using DVOM, check resistance between test harness terminals No. 2 (White clip) and either 1 (Red clip) or 3 (Blue clip), and between test harness terminals No. 5 (Green clip) and either 4 (Black clip) or 6 (Yellow clip). Resistance should be 28-33 ohms at 68°F (20°C). If resistance is as specified, go to next step. If resistance is not as specified, replace IAC motor. Go to step 10).
On 3000GT, go to step 7). On Montero, disconnect IAC motor connector and MFI relay connector. Check for continuity between IAC motor connector terminal No. 2 and MFI relay connector terminal No. 1. If continuity does not exist, repair wiring harness as necessary. If continuity exists, go to next step.
Check for continuity between IAC motor connector terminal No. 5 and MFI relay connector terminal No. 1. If continuity does not exist, repair wiring harness as necessary. If continuity exists, go to next step.
Disconnect IAC motor connector. Turn ignition switch to ON position. Check voltage between chassis ground and IAC motor connector terminals No. 2 and 5. If battery voltage does not exist on either circuit, repair wiring harness as necessary. If battery voltage exists on both circuits, go to next step.

Turn ignition switch to OFF position. Disconnect PCM connector and IAC motor connector. Ground specified PCM connector terminal and using DVOM, check continuity between chassis ground and specified IAC motor connector terminal. See PCM-TO-IAC MOTOR HARNESS CIRCUIT IDENTIFICATION table. If continuity does not exist, repair wiring harness as necessary. If continuity exists, go to next step.

PCM-TO-IAC MOTOR HARNESS CIRCUIT IDENTIFICATION

PCM Terminal No.	IAC Motor Terminal No.
14	1
15	4
28	3
29	6

Test is complete. Intermittent problem may exist. Road test vehicle (if necessary) and attempt to duplicate conditions that caused original complaint. Recheck for DTCs. If no DTCs are displayed, go to INTERMITTENT DTCS .
Road test vehicle and attempt to duplicate conditions that caused original complaint. Recheck for DTCs. If no DTCs are displayed, test is complete.