DTC P0505: IDLE CONTROL SYSTEM MALFUNCTION Toyota Tundra I

Circuit Description

Engine Control Module (ECM) operates Idle Air Control (IAC) valve to perform idle-up and provide feedback for target idling speed. DTC is set when idle speed continues to vary greatly from target speed. Possible causes are

1. IAC valve is stuck or remains closed.
2. IAC valve circuit is open or shorted.
3. A/C signal circuit is open or shorted.
4. Air induction system malfunction.
5. Defective ECM.

Diagnostic Aids

Using Toyota hand-held tester or scan tool, read FREEZE FRAME data. Freeze frame records engine conditions when malfunction is detected.

Scheme 263

1. Start engine and warm to engine to normal operating temperature. Ensure A/C and all accessories are off. Apply parking brake. Place transmission in Neutral. Install jumper wire (SST 09843-18020) between TC and CG terminals on Data Link Connector (DLC) No. 3. (Scheme 263) Note engine speed in less than 5 seconds and at more than 5 seconds after installling jumper wire. If difference in engine speed is 100 RPM or less, go to next step. If difference in engine speed is more than 100 RPM, go to step 6.
2. Turn ignition off. Remove glove box and heater duct (if necessary) for access to ECM with electrical connectors still installed on ECM. see scheme 2 Disconnect ECM electrical connector E7. see scheme 4
3. Turn ignition on. Using voltmeter, check voltage between body ground and terminals No. 15 (Black/Red wire) and No. 16 (Red/White wire) at ECM electrical connector E7. see scheme 4 This is the RSC and RSO terminals on ECM. Voltage should be 9-14 volts. If voltage is within specification, go to next step. If voltage is not within specification, check IAC valve operation. See IDLE AIR CONTROL VALVE under IDLE CONTROL SYSTEMS in SYSTEM & COMPONENT TESTING - V6 & V8 article. If IAC valve is defective, replace IAC valve. If IAC valve is okay, check for open and short in wiring harness and electrical connectors between IAC valve and ECM, and between IAC valve and EFI main relay. See WIRING DIAGRAMS article. EFI main relay may also be referred to as EFI relay. EFI main relay is located in fuse/relay box at driver's side front corner of engine compartment. Repair wiring as necessary.
4. Check IAC valve operation. See IDLE AIR CONTROL VALVE under IDLE CONTROL SYSTEMS in SYSTEM & COMPONENT TESTING - V6 & V8 article. If IAC valve is okay, go to next step. If IAC valve is defective, replace IAC valve.
5. Remove IAC valve from throttle body. Inspect IAC valve and passages for carbon build-up and blockage. If a problem exist, repair as necessary. If problem does not exist, replace ECM.
6. Ensure engine oil dipstick, oil filler cap, PCV system and all other air induction system components are intact and operating properly. If problem exists, repair as necessary. If problem does not exist, an open and short in A/C signal circuit may exist. Check A/C control assembly which may also be referred to as center cluster integration. See MANUAL A/C-HEATER SYSTEMS article in AIR CONDITIONING & HEATING. Repair as necessary.