Circuit Description

PCM controls idle speed by adjusting an Idle Air Control (IAC) valve to a calculated RPM based on sensor inputs and actual engine RPM. PCM moves IAC pintle valve in or out to vary amount of air flowing into intake manifold, and thus decrease or increase idle RPM. PCM commands IAC in counts. A higher count allows more air to by-pass throttle plate (higher idle). When PCM detects too low of an idle speed and is unable to adjust idle speed, DTC P0506 will set.

Conditions required to set DTC are:

• NO intrusive tests being run.
• Engine run time is more than 360 seconds.
• No TP, VSS, ECT, EGR, MAP, IAT, misfire, low voltage, fuel system, CKP, injector, HO2S, VSS or canister purge DTCs set.
• BARO is greater than 72.7 kPa.
• Canister purge duty cycle is greater than zero percent.
• Engine coolant temperature is greater than 122°F (50°C).
• Intake air temperature is more than -40° (-40°C).
• MAP is less than 60 kPa.
• Ignition voltage is 9.5-16 volts.
• Throttle is closed.
• Engine speed is 100 RPM less than desired idle.
• Listed conditions are met for greater than 10 seconds.