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
Test Enable (Non-Intrusive Test)
| • | No TP sensor DTCs are set |
| • | No VS sensor DTCs are set |
| • | No ECT sensor DTCs are set |
| • | No MAP sensor DTCs are set |
| • | The ECT is more than 72°C. |
| • | The ignition voltage is between 10-18 volts. |
| • | The IAT is more than -25°C. |
| • | The engine run time is more than 30 seconds. |
| • | The BARO is more than 70 kPa. |
| • | The TP sensor is less than 1%. |
| • | The VS is less than 2 mph. |
| • | The above conditions are met for more than 3 seconds. |
| • | If the VCM detects the engine speed is 100 RPM less than the desired engine speed, the intrusive test is run. |
Test Run (Intrusive Test)
| • | The MAF sensor is between 17.5-37.5 grams per second. |
| • | The VS is between 35-85 mph. |
| • | The TP angle does not change more than 1%. |
| • | The engine speed does not change more than 30 RPM. |
| • | The IAC motor will be commanded open a small amount and the MAF change will be recorded. If the MAF does not change a predetermined amount, DTC P0506 will set. |
| • | The above conditions are present for 10 seconds. |
Action Taken When the DTC Sets
The VCM turns the MIL ON 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 the DTCs, use the scan tool to record the Freeze Frame and the Failure Records for reference. This data will be lost when the Clear Info function is used. 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. | -- | -- | |
5 | Problem is engine mechanical related. | -- | -- | |
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 |
