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Idle Air Control (IAC) Valve Assembly Malfunction

NOTE: The following test procedures are for DTCs P0505, P0506, P1504 and P1507.
Fig 1: Idle Air Control (IAC) Valve Assembly Malfunction Detection Condition Possible Cause
G03723711Courtesy of MAZDA MOTORS CORP.
IDLE AIR CONTROL (IAC) VALVE ASSEMBLY MALFUNCTION INSPECTION/ACTION CHART

STEP INSPECTION ACTION
1
  • Was PCM Quick Test performed? 
 Yes Go to next step.
No Perform PCM Quick Test. See PCM QUICK TEST  .
2 DTC P0505, P0506, 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 DTC P0402 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 voltage greater than 10.5 volts? 
 Yes Go to next step.
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 resistance between 6.0 and 13.0 ohms? 
 Yes Go to next step.
No Replace IAC assembly.
See IDLE AIR CONTROL (IAC) VALVE -- 2.3L or IDLE AIR CONTROL (IAC) VALVE -- 3.0L (4V) .
Go to step 12.
4 CHECK IAC VALVE ASSEMBLY FOR AN INTERNAL SHORT TO IAC CASE
  • Measure resistance from IAC valve pin (W/LB) to IAC valve case.
  • Is resistance greater than 10K ohms? 
 Yes For DTC P1504:
Go to step 7.
All others:
Go to next step.
No Replace IAC valve.
See IDLE AIR CONTROL (IAC) VALVE -- 2.3L or IDLE AIR CONTROL (IAC) VALVE -- 3.0L (4V) .
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.
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 assembly 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 next step.
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 E39 and the IAC valve harness connector.
  • Is resistance less than 5.0 ohms? 
 Yes Go to next step.
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 E39 (IAC) and body ground.
  • Key OFF.
  • Was voltage less than 1.0 V? 
 Yes Go to next step.
No Repair short circuit.
Go to step 12.
9 CHECK IAC CIRCUIT FOR SHORT TO GROUND
  • Disconnect WDS or equivalent tester from DLC.
  • Measure resistance between PCM test pin E39 (IAC) and PCM test pin C49 (PWR GND).
  • Is each resistance greater than 10K ohms? 
 Yes Go to next step.
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 WDS or equivalent tester.
  • Key On, Engine Running (KOER).
  • Using WDS or equivalent tester, select Diagnostic Data Link.
  • Select PCM
  • Select PID Data Monitor and Record.
  • 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 next step.
All others:
Key OFF.
Inspect throttle body for damage.
Repair as necessary.
If OK, replace IAC valve.
See IDLE AIR CONTROL (IAC) VALVE -- 2.3L or IDLE AIR CONTROL (IAC) VALVE -- 3.0L (4V) .
Go to step 12.
No For DTC P1507, replace IAC valve.
See IDLE AIR CONTROL (IAC) VALVE -- 2.3L or IDLE AIR CONTROL (IAC) VALVE -- 3.0L (4V) .
Otherwise, replace PCM.
See POWERTRAIN CONTROL MODULE (PCM) .
Go to step 12.
11 CHECK IAC SYSTEM FOR INTERMITTENT OPEN OR SHORT
  • Using WDS or equivalent tester, select Diagnostic Data Link.
  • Select PCM
  • Select PID Data Monitor and Record.
  • Access IAC and RPM PIDs.
  • 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 next step.
No For idle quality, starting or stalling symptoms currently present:
Replace IAC valve.
See IDLE AIR CONTROL (IAC) VALVE -- 2.3L or IDLE AIR CONTROL (IAC) VALVE -- 3.0L (4V) .
Go to next step.
All others:
Unable to duplicate or identify fault at this time.
See TEST 3: INTERMITTENT  .
12 VERIFY TROUBLESHOOTING OF DTCs COMPLETED
  • Make sure to reconnect all disconnected connectors.
  • Clear DTCs from PCM memory using WDS or equivalent tester generic OBD II function.
  • Perform PCM Quick Test. See PCM QUICK TEST  .
  • Is same DTC present? 
 Yes Replace PCM.
See POWERTRAIN CONTROL MODULE (PCM) .
Repeat PCM Quick Test. See PCM QUICK TEST  .
No If any other DTC is present, go to applicable DTC inspection.
If no DTC is present, troubleshooting complete.
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