Idle Air Control (IAC) Valve Assembly Malfunction

DTC P0505, P1504, P1507 DETECTION CONDITION AND POSSIBLE CAUSE

DTC P0505, P1504, P1507	IDLE AIR CONTROL (IAC) VALVE ASSEMBLY MALFUNCTION
DETECTION CONDITION	P0505 indicates the desired RPM could not be reached or controlled during KOEO Self Test. P1504 indicates an electrical load failure on IAC output circuit. P1507 indicates the engine idle speed is less than desired RPM.
POSSIBLE CAUSE	VPWR to IAC solenoid open (P0505, P1504, P1507). IAC circuit open (P0505, P1504, P1507). IAC circuit shorted to PWR (P0505, P1504, P1507). IAC circuit short to GND (P1504). VPWR circuit open (P0505, P1504, P1507). Air inlet plugged (P0505, P1507). Air inlet leakage (P1507). Damaged IAC solenoid (P1504, P1507). Damaged throttle body (P0505, P1507). Damaged PCM (P0505, P1504, P1507).
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 the IAC valve to control the amount of air bypass air.
Courtesy of MAZDA MOTORS CORP.

DTC P0505, P1504, P1507 INSPECTION

STEP	INSPECTION		ACTION
1	Was PCM Quick Test performed?	Yes	Go to next step.
1	Was PCM Quick Test performed?	No	Perform PCM Quick Test.
2	DTC P0505, P1504, P1507 OR STARTS ONLY AT PART THROTTLE: CHECK VPWR TO IAC VALVE ASSEMBLY NOTE: If EGR DTC P0402 was output during Self Test, diagnose it first before continuing with this test. Disconnect IAC valve. Key ON, Engine OFF (KOEO). Measure voltage between VPWR at the IAC valve harness connector and ground. Key OFF. Was the voltage greater than 10.5 V?	Yes	Go to next step.
2		No	Repair open in VPWR circuit. Go to step 12.
3	CHECK IAC VALVE RESISTANCE NOTE: Due to diode in solenoid, place DVOM positive lead on VPWR pin and negative lead on IAC pin. Measure valve assembly resistance. Is the resistance between 6.0 and 13.0 ohms?	Yes	Go to next step.
3		No	Replace IAC assembly. Go to step 12.
4	CHECK IAC VALVE FOR AN INTERNAL SHORT TO IAC CASE Measure resistance from IAC valve pin to IAC valve case. Is the resistance greater than 10K ohms?	Yes	For DTC P1504: Go to step 7. All others: Go to next step.
4		No	Replace IAC valve. Go to step 12.
5	CHECK AIR INLET FOR PLUGGING Inspect entire air intake system for debris, blockage and other damage. Remove and inspect the air cleaner element for excessive dirt. Is the air intake system OK?	Yes	Restore inlet air system. Go to next step.
5		No	Repair as necessary. Go to step 12.
6	CHECK FOR VACUUM LEAKS Key ON, Engine Running (KOER). With engine running at idle, listen for vacuum leaks. Inspect the entire air intake system from the Mass Air Flow (MAF) sensor to the intake manifold for leaks such as: Cracked or punctured intake air tube. Loose intake air tube at air cleaner housing or throttle body. IAC valve or gasket seal. EGR valve gasket seal. Vacuum supply connector and hose. PCV connectors and hose. Key OFF. Were any leaks detected in the above areas?	Yes	Repair as necessary. Go to step 12.
6		No	Go to next step.
7	CHECK IAC CIRCUIT RESISTANCE Disconnected PCM and IAC valve. Install Breakout Box, leave PCM disconnected. Measure resistance of IAC circuit between PCM test pin 83 and the IAC valve harness connector. Is the resistance less than 5.0 ohms?	Yes	Go to next step.
7		No	Repair open circuit. Go to step 12.
8	CHECK IAC CIRCUIT FOR SHORT TO PWR Key ON, Engine OFF (KOEO). Measure voltage between PCM test pin 83 (IAC) and body ground. Key OFF. Was the voltage less than 1.0 V?	Yes	Go to next step.
8		No	Repair short circuit. Go to step 12.
9	CHECK IAC CIRCUIT FOR SHORT TO GROUND Disconnect NGS Tester from DLC. Measure resistance between PCM test pin 83 (IAC) and PCM test pin 103 (PWR GND). Is each resistance greater than 10K ohms?	Yes	For DTC 1504, replace PCM. See COMPUTERIZED ENGINE CONTROLS . Go to step 12. All others: Go to next step.
9		No	Repair short circuit. Go to step 12.
10	CHECK IAC SIGNAL FROM PCM Remove Breakout Box. Reconnect PCM and IAC valve. NOTE: If stalling occurs, place a shim under the hard stop screw to maintain idle conditions. Reconnect NGS Tester. Key On, Engine Running (KOER). Access IAC and RPM PIDs. With engine at normal operating temperature, all accessories OFF and at closed throttle, the IAC duty cycle must be between approximately 22 percent and 45 percent. Slowly increase engine speed to 3000 rpm and return to closed throttle. NOTE: If closed throttle rpm is significantly higher than normal, ignore this step. Is the IAC duty cycle within specification at closed throttle and does the duty cycle respond to the change in rpm?	Yes	For Continuous Memory DTCs P1504 and P1507: Go to step 11. All others: Key OFF. Inspect throttle body for damage. Repair as necessary. If OK, replace IAC valve. Go to step 12.
10		No	For DTC P1507, replace IAC valve. Otherwise, replace PCM. See COMPUTERIZED ENGINE CONTROLS . Go to step 12.
11	CHECK IAC SYSTEM FOR INTERMITTENT OPEN OR SHORT Access IAC and RPM PIDs with an NGS Tester. Observe the PIDs for an indication of a fault while performing the following at idle: Lightly tap on IAC valve and wiggle harness connector to simulate road shock. Grasp vehicle harness closest to the IAC valve. 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 and RPM PIDs suddenly change in value indicating a fault?	Yes	Isolate fault and repair as necessary. Go to step 12.
11		No	For idle quality, starting or stalling symptoms currently present: Replace IAC valve. Go to step 12. All others: Unable to duplicate or identify fault at this time. See TEST 4: INTERMITTENT with the following data.
12	VERIFY TROUBLESHOOTING OF DTCs COMPLETED Make sure to reconnect all disconnected connectors. Clear DTCs from PCM memory using NGS tester generic OBD-II function. Perform PCM Quick Test. Is same DTC present?	Yes	Replace PCM. See COMPUTERIZED ENGINE CONTROLS . Repeat PCM Quick Test.
12		No	If any other DTC is present, go to applicable DTC inspection. If no DTC is present, troubleshooting complete.