The PCM controls engine idle speed by adjusting the position of the Idle Air Control (IAC) motor pintle. The IAC is a bi-directional motor driven by two coils. The PCM sends pulses (steps) to the IAC to extend or retract the IAC pintle into a passage in the throttle body to decrease or increase air flow. The commanded IAC position (displayed in counts) can be monitored on the scan tool; a higher number of counts indicates more commanded airflow (pintle retracted) This method allows highly accurate control of idle speed and quick response to changes in engine load. If the PCM detects a condition where too low of an idle speed is present and the PCM is unable to adjust idle speed by increasing the IAC counts, DTC P0506 will set indicating a problem with the idle control system.
• | No VSS, CCP,TP sensor, misfire, IAT sensor, MAP sensor, fuel trim, fuel injector, EGR, ECT sensor, CKP sensor, or MAF sensor DTCs set. |
• | Vehicle Speed is less than 3 MPH. |
• | Engine has been running for at least 2 minutes. |
• | System voltage is between 9 and 18 volts. |
• | VIN K -- BARO is greater than 65 kPa. |
• | VIN 1 -- BARO is greater than 70 kPa. |
• | VIN K -- Engine Coolant Temperature is greater than -40°C (-40°F). |
• | VIN 1 -- Engine Coolant Temperature is greater than 70°C (158°F). |
• | VIN K -- Intake Air Temperature is greater than -40°C (-40°F). |
• | VIN 1 -- Intake Air Temperature is greater than -18°C (-4°F). |
• | VIN K -- The throttle is closed. |
• | VIN 1 -- The throttle is closed. |
• | VIN K -- Engine Speed is more than 150 RPM lower than Desired Idle (negative idle speed error greater than 150 RPM). |
• | VIN 1 -- Engine Speed is more than 175 RPM lower than Desired Idle (negative idle speed error greater than 175 RPM). |
• | Above conditions for longer than 15 seconds. |
• | The PCM illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails. |
• | The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. |
• | The PCM writes the conditions to the Freeze Frame and updates the Failure Records. |
• | The PCM will turn OFF the malfunction indicator lamp (MIL) during the third consecutive trip in which the diagnostic has run and passed. |
• | The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction. |
• | The DTC can be cleared by using a scan tool. |
Check for the following conditions:
• | Poor connection at PCM or IAC motor. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection. |
• | Damaged harness. Inspect the wiring harness for damage. |
• | Restricted air intake system. Check for a possible collapsed air intake duct, restricted air filter element, or foreign objects blocking the air intake system. |
• | Throttle body. Check for objects blocking the IAC passage or throttle bore, excessive deposits in the IAC passage and on the IAC pintle, and excessive deposits in the throttle bore and on the throttle plate. |
• | Large vacuum leak. Check for a condition that causes a large vacuum leak, such as an incorrectly installed or malfunctioning crankcase ventilation valve or brake booster hose disconnected. |
Reviewing the Fail Records vehicle mileage since the diagnostic test last failed may help determine how often the condition that caused the DTC to be set occurs. This may assist in diagnosing the condition.
Number(s) below refer to the step number(s) on the Diagnostic Table.
Step | Action | Value(s) | Yes | No | ||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
1 | Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | ||||||||||
2 | Are any other DTCs set? | -- | Go to applicable DTCs | |||||||||
3 |
Does Engine Speed remain within the specified value of Desired Idle for each RPM command? | ± 100 RPM | Go to Diagnostic Aids | |||||||||
4 |
Does each node light cycle red and green (never OFF)? | -- | ||||||||||
5 |
Was a problem found? | -- | ||||||||||
6 |
Was a problem found? | -- | ||||||||||
7 |
Was a problem found? | -- | ||||||||||
8 | Replace the IAC valve. Refer to Idle Air Control Valve Replacement . Is action complete? | -- | -- | |||||||||
9 |
Was a problem found? | -- | ||||||||||
Important:: The replacement PCM must be programmed. Refer to Powertrain Control Module Replacement/Programming . Replace the PCM. Is action complete? | -- | -- | ||||||||||
11 |
Does Engine Speed remain within the specified value of Desired Idle for each RPM command? | ± 100 RPM | System OK |