Idle Air Control (IAC) System Malfunction

DTC P1506 DETECTION CONDITION & POSSIBLE CAUSES

DTC P1506	IDLE AIR CONTROL (IAC) SYSTEM MALFUNCTION
DETECTION CONDITION	P1506 indicates that the powertrain control module (PCM) detected an engine idle speed greater than the desired rpm.
POSSIBLE CAUSE	Vacuum leak Damaged IAC valve Damaged PCM Damaged throttle body IAC circuit short to GND IAC valve stuck open
HINT	IAC Valve Description Controls engine idle speed and provides a dashpot function. Meters intake air around the throttle plate through a bypass within the IAC valve assembly and throttle body. The PCM determines the desired idle speed or bypass air and signals the IAC valve assembly through a specified duty cycle. The IAC valve responds by positioning itself to control the amount of bypassed air. The PCM monitors the engine rpm and increases or decreases the IAC duty cycle in order to achieve the desired rpm.
Courtesy of MAZDA MOTORS CORP.
Courtesy of MAZDA MOTORS CORP.

DTC P1506 DIAGNOSTIC PROCEDURE

DTC P1506		IDLE AIR CONTROL (IAC) SYSTEM MALFUNCTION
STEP	INSPECTION		ACTION
1	Was the PCM quick test performed?	Yes	Go to next step.
1	Was the PCM quick test performed?	No	Perform PCM quick test. See PCM QUICK TEST .
2	DTC P1506: CHECK FOR VACUUM LEAKS Key on, engine running (KOER). With the engine at idle, listen for vacuum leaks. Inspect the entire intake air system from the mass air flow (MAF) sensor to the intake manifold for damage or leaks such as: Cracked or punctured intake air tube Loose or cracked IAC air tubes Loose intake air tube at the air cleaner housing or throttle body IAC valve assembly or gasket seal Intake manifold assembly or gasket seal EGR valve gasket seal Vacuum supply connectors and hose PCV valve, connectors and hoses Key OFF. Are any leaks detected?	Yes	Repair or replace components as necessary. Go to step 7.
2		No	Go to next step.
3	CHECK EVAP SYSTEM FOR A STUCK OPEN VALVE Disconnect hoses at EVAP canister purge solenoid. Connect hand vacuum pump to port A of EVAP canister purge solenoid. Fig 1: Identifying Port A Of EVAP Canister Purge Solenoid Courtesy of MAZDA MOTORS CORP. Apply 53 kPa (16 in-Hg) of vacuum to EVAP canister purge solenoid. Does EVAP canister purge solenoid hold vacuum for 20 seconds?	Yes	Connect all components. Go to next step.
3		No	Replace EVAP canister purge solenoid. See CANISTER PURGE VALVE REMOVAL / INSTALLATION . Go to step 7.
4	CHECK EVAP SYSTEM FOR A STUCK OPEN VALVE Key on, engine running (KOER). Verify engine at normal operating temperature. Transmission in park or neutral. Disconnect IAC valve connector. Key OFF. Does the rpm drop or engine stall when IAC valve disconnected?	Yes	Go to next step.
4		No	Inspect throttle body for damage. If OK: Replace IAC valve. See IDLE AIR CONTROL (IAC) VALVE REMOVAL / INSTALLATION - 2.3L for 2.3L engine or see IDLE AIR CONTROL (IAC) VALVE REMOVAL / INSTALLATION - 3.0L for 3.0L engine or see IDLE AIR CONTROL (IAC) VALVE REMOVAL / INSTALLATION - 4.0L . If not OK: Repair or replace throttle body. See THROTTLE BODY REMOVAL / INSTALLATION - 2.3L for 2.3L engine THROTTLE BODY REMOVAL / INSTALLATION - 3.0L for 3.0L engine or THROTTLE BODY REMOVAL / INSTALLATION - 4.0L for 4.0L engine. Go to step 7.
5	CHECK IAC CIRCUIT FOR SHORT TO GROUND Disconnect WDS or equivalent tester. Disconnect PCM. Install breakout box, leave PCM disconnected. Measure resistance of IAC SIG circuit between PCM test pin 83 (IAC) and PCM test pins 51 and 103 (PWR GND). Is resistance greater than 10K ohms?	Yes	For fast idle symptom currently present: replace PCM. See POWERTRAIN CONTROL MODULE (PCM) REMOVAL / INSTALLATION . Go to step 7. All others: Go to next step.
5		No	Repair short in IAC SIG circuit. Go to step 7.
6	CHECK IAC SYSTEM FOR INTERMITTENT OPEN OR SHORT Connect scan tool. Key on, engine running (KOER). Using WDS or equivalent tester, select Diagnostic Data Link. Select PCM. Select PID/Data Monitor and Record. Access IAC PID and RPM PIDs. With engine at normal operating temperature, accessories off and at idle, the IAC duty cycle must be between 20% and 45%. Observe the PIDs for an indication of a fault while performing the following at idle: Lightly tap on IAC valve assembly and wiggle harness connector to simulate road shock Grasp the vehicle harness closest to the IAC valve assembly. Shake and bend a small section of the harness from the IAC to the dash panel and from the dash panel to the PCM Do the IAC or RPM PIDs suddenly change in value indicating a fault?	Yes	Isolate fault and repair as necessary. Go to next step.
6		No	For idle quality, starting or stalling symptoms currently present: replace IAC solenoid. See IDLE AIR CONTROL (IAC) VALVE REMOVAL / INSTALLATION - 2.3L for 2.3L engine or see IDLE AIR CONTROL (IAC) VALVE REMOVAL / INSTALLATION - 3.0L for 3.0L engine or see IDLE AIR CONTROL (IAC) VALVE REMOVAL / INSTALLATION - 4.0L . Go to next step. All others: See GENERAL PINPOINT TEST 4: INTERMITTENT with IAC and RPM PID data and list of possible causes.
7	VERIFY TROUBLESHOOTING OF DTCs COMPLETED Connect all disconnected connectors. Clear DTCs from PCM memory using WDS or equivalent tester. Perform PCM quick test. Is same DTC present?	Yes	Replace PCM. See POWERTRAIN CONTROL MODULE (PCM) REMOVAL / INSTALLATION . Repeat PCM quick test.
7		No	If any other DTC is present, go to applicable DTC inspection. See DIAGNOSTIC TROUBLE CODE (DTC) INDEX - POWERTRAIN CONTROL MODULE (PCM) . If no DTC is present, troubleshooting is complete.