Circuit Description
The VCM controls the idle speed with an Idle Air Control (IAC) valve to a calculated desired RPM based on the sensor inputs and the actual engine RPM. The VCM uses 4 circuits in order to move an Idle Air Control (IAC) valve, allowing a varying amount of air flow into the intake manifold.
In order to increase the idle RPM, the VCM moves the IAC valve out, allowing more air to bypass the throttle plate. In order to decrease the RPM, the VCM moves the IAC valve in, reducing the amount of air bypassing the throttle plate. A scan tool reads the VCM commands to the IAC valve in counts. The higher the counts, the more air is allowed to bypass the throttle plate (higher idle). The lower the counts, the less air that is allowed to bypass the throttle plates (lower idle). This DTC is a type B DTC.
Conditions for Setting the DTC
The following conditions will set the DTC:
| • | No TP sensor DTCs |
| • | No VS sensor DTCs |
| • | No ECT sensor DTCs |
| • | No MAP sensor DTCs |
| • | No EST DTCs |
| • | No IAT DTCs |
| • | No Camshaft Position sensor DTCs |
| • | ECT greater than 50°C |
| • | IAT greater than -25°C |
| • | Baro greater than 70 kPa (75 kPa for 7.4L)) |
| • | VS less than 2 mph |
| • | System voltage greater than 10 volts but less than 16 volts |
| • | Engine run time greater than 30 seconds |
| • | TP less than 1% |
| • | Above met for a time greater than 3 seconds in order to enable diagnostic |
Run Test (Intrusive)
| • | Air flow is greater than 17.5 g/s but less than 50 g/s |
| • | VS is greater than 25 MPH but less than 85 MPH |
| • | Variation in TP is less than 1% |
| • | Variation in Engine speed is less than 50 RPM |
| • | IAC motor commanded 10% per 100 ms |
Action Taken When the DTC Sets
The VCM will turn ON the MIL after 2 consecutive driving cycles with the fault active.
Conditions for Clearing the MIL/DTC
The VCM turns OFF the MIL after 3 consecutive driving trips without a fault condition present. A history DTC will clear if no fault conditions have been detected for 40 warm-up cycles (the coolant temperature has risen 22°C (40°F) from the start-up coolant temperature and the engine coolant temperature exceeds 71°C (160°F) during that same ignition cycle) or the scan tool clearing feature has been used.
Diagnostic Aids
The following items could cause this DTC:
| • | An IAC valve which is stopped and cannot respond to the VCM |
| • | A throttle stop screw which has been tampered with |
| • | A damaged throttle or linkage |
A slow, unstable, or fast idle may be caused by a non - IAC valve system problem that cannot be overcome by the IAC valve. Out of range control IAC scan tool counts will read above 60 if the idle is too low and zero if the idle is too high. Check for the following:
| • | Fuel system too lean and rich |
| • | Throttle body - inspect the bore for foreign material. |
| • | Refer to Rough, Unstable, or Incorrect Idle and Stalling . |
| • | IAC reset is done with the scan tool misc. functions mode. |
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 |
Important: Before clearing DTCs, use the scan tool in order to record the freeze frame and the failure records for reference because the Clear Info function will lose the data. Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | ||
2 | Install the scan tool. Are any other DTCs set? | -- | Go to The Applicable DTC Table | |
3 | Is the DTC P0506 active this ignition cycle? | -- | ||
4 | This DTC is an intermittent. Refer to the Diagnostic Aids. Is the action complete? | -- | -- | |
5 | Problem is engine mechanical related. Refer to Engine Mechanical. Is the action complete? | -- | -- | |
6 |
Does the scan tool indicate that this diagnostic ran and passed? | -- | ||
7 | Using the scan tool, select the Capture Info and the Review Info. Are any DTCs displayed that have not been diagnosed? | -- | Go to The Applicable DTC Table | System OK |
