Mazda MX-6 1998, Workshop Manual, Page: 109 / 1282

TROUBLESHOOTING [ENGINE CONTROL FS]
DTC P0505
P1504
P1507
Idle air control (IAC) system malfunction
Idle air control (IAC) valve circuit malfunction
Idle air control (IAC) system underspeed error
DESCRIPTION
• DTC P0505 indicates IAC system malfunction
• DTC P1504 indicates IAC valve circuit malfunction
• DTC P1507 indicates IAC underspeed error
[Possible Cause]
• IAC valve signal circuit open • Air inlet leakage (PI 507)
• IAC valve signal circuit shorted to power circuit • Damaged IAC valve component
• IAC valve signal short to ground (P1504) • Damaged throttle body (P0505, P1507)
• IAC valve power circuit open • Damaged PCM
• Air inlet plugged (P0505, P1507)
STEP
INSPECTION ACTION
1 CHECK POWER CIRCUIT TO IAC VALVE
• Key off.
• Disconnect IAC valve vehicle harness
connector.
• Key on.
• Measure voltage between power circuit at
IAC valve vehicle harness connector and
battery ground.
• Is voltage greater than 10.5 volts?
Yes Go to next step.
No SERVICE open in power circuit to IAC valve.
RECONNECT all components.
RERUN OBD Test.
2 CHECK IAC VALVE RESISTANCE
• Key off.
• IAC valve connector disconnected.
• Measure solenoid resistance.
Note
• Due to diode in solenoid, place DVOM (+)
lead on power circuit pin and (-) lead on
IAC valve pin.
• Is resistance between 6.0 and 13.0
ohms?
Yes Go to next step.
No REPLACE IAC valve assembly.
RECONNECT all components.
RERUN OBD Test.
3
CHECK IAC VALVE FOR AN INTERNAL
SHORT TO IAC CASE
• Key off.
• IAC valve connector disconnected.
• Measure resistance from either IAC valve
pin to IAC valve assembly case.
• Is resistance greater than 10,000 ohms?
Yes For DTC P1504:
Go to step 6.
All others:
Go to next step.
No REPLACE IAC valve assembly.
RECONNECT all components.
RERUN OBD Test.
4 CHECK AIR INLET FOR PLUGGING
• Key off.
• Inspect entire air inlet system for debris
blockage and other damage.
• Remove and inspect air filter element for
excessive dirt.
• Is air inlet system okay?
Yes Go to next step.
No SERVICE as necessary.
RECONNECT all components.
RERUN OBD Test.
5
CHECK FOR VACUUM LEAKS
• Key on, engine running.
• With engine running at idle, listen for
vacuum leaks.
• Inspect the entire air inlet system from MAF
sensor to intake manifold for leaks such as:
• Cracked or punctured air inlet tube
• Loose air inlet tube at air cleaner
housing or throttle body
• IAC valve assembly or gasket seal
• EGR valve gasket seal
• Vacuum supply connector and hose
• Positive crankcase ventilation (PCV)
valve connectors and hose
• Are any leaks detected In above areas?
Yes SERVICE as necessary.
RECONNECT all components.
RERUN OBD Test.
No Go to next step.
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