DTC P0505 - Idle Control System Failure

NOTE: For component terminal identification, see TERMINAL IDENTIFICATION in this article. For wiring diagrams, see WIRING DIAGRAMS article.

Manufacturer does not provide component testing procedure without using scan tool. Ensure engine coolant temperature is 185-205°F (85-95°C). Place transmission in Park or Neutral. Turn off all accessories except A/C. Ensure A/C clutch is operating when A/C system is on. Allow engine to idle. Go to next step.

Using scan tool, read Idle Air Control (IAC) position sensor step. 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 next step.

IAC POSITION SENSOR STEP SPECIFICATIONS

A/C Switch Position

Standard Step Value

Off

2-25

Increase From 10-70

⁽¹⁾

Increase From 5-50

⁽¹⁾	For A/T models. Brakes applied, transmission in Drive and A/C on.

On Diamante, go to step 7). On Stealth and 3000GT, go to step 9). Turn ignition switch to OFF position. Disconnect PCM connector and IAC position sensor connector. Ground specified PCM connector terminal and using DVOM, check continuity between chassis ground and specified IAC connector terminal. See PCM-TO-IAC HARNESS CIRCUIT IDENTIFICATION table. If continuity does not exist, repair wiring harness as necessary. If continuity exists, go to next step.

PCM-TO-IAC HARNESS CIRCUIT IDENTIFICATION

Application	PCM Terminal No.	IAC Motor Terminal No.
All Models	5	2
18		4
61		1

With IAC position sensor connector disconnected, check continuity between chassis ground and IAC position sensor connector terminal No. 3. If continuity does not exist, repair wiring harness as necessary. If continuity exists, go to next step.
Reconnect PCM connector. Turn ignition switch to ON position. With IAC position sensor connector disconnected, turn ignition switch to ON position. Check for voltage between chassis ground and IAC connector terminals No. 2 and 4. If voltage is not 4.8-5.2 volts on either circuit, replace PCM. If voltage is as specified, go to next step.
Check voltage between chassis ground and IAC position sensor connector terminal No. 1. If voltage is not 4.8-5.2 volts, replace PCM. If voltage is as specified, condition required to set DTC is not present at this time. Go to step 10).
Disconnect IAC motor connector and MFI relay connector. Check for continuity between IAC motor connector terminal No. 5 and MFI relay connector terminal No. 3. If continuity does not exist, repair wiring harness as necessary. If continuity exists on Diamante, go to step 10).
Check for continuity between IAC motor connector terminal No. 2 and MFI relay connector terminal No. 3. 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

Application	PCM Terminal No.	IAC Motor Terminal No.
All Models	4	1
5		4
17		3
18		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 .