DTC P0506 Idle Speed Low. Oldsmobile Eighty Eight 1999

For 1990-2009 cars only

Makes 🢒 Oldsmobile 🢒 1999 🢒 Eighty Eight 🢒 Engine 🢒 Engine Controls - 3.8L 🢒 DTC P0506 Idle Speed Low

Engine Controls Components
Engine Controls Schematics
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice

Circuit Description

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.

Conditions for Running the DTC

•	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 position is below .25%.

•	VIN 1 -- The throttle position is below 1.31%.

Conditions for Setting the DTC

•	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 are present for longer than 15 seconds.

Action Taken When the DTC Sets

•	The PCM will illuminate the malfunction indicator lamp (MIL) during the second consecutive trip in which the diagnostic test has been run and failed.

•	The PCM will store conditions which were present when the DTC set as Freeze Frame and Failure Records data.

Conditions for Clearing the MIL/DTC

•	The PCM will turn OFF the MIL during the third consecutive trip in which the diagnostic has been 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 the scan tool.

Diagnostic Aids

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 a 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.

Test Description

The numbers below refer the step numbers on the diagnostic table.

This vehicle is equipped with a PCM which utilizes an Electrically Erasable Programmable Read Only Memory (EEPROM). When the PCM is being replaced, the new PCM must be programmed. Refer to PCM Replacement/Programming .

DTC P0506 - Idle Air Control System RPM Low

Step

Action

Value(s)

Yes

Was the Powertrain On-Board Diagnostic (OBD) System Check performed?

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

Are any other DTCs set?

Diagnose the other DTC first - Go to Powertrain Control Module Diagnosis

Go to Step 3

Start the engine.
Turn OFF all accessories (A/C, Rear defroster etc.).
Using a scan tool, command RPM up to 1500, down to 650, and then up to 1500 while monitoring Engine Speed on the scan tool.

Does Engine Speed remain within the specified value of Desired Idle for each RPM command?

± 100 RPM

Go to Diagnostic Aids

Go to Step 4

Disconnect the IAC.
Install a Scan Tool.
With the engine running, command RPM up to 1500, down to 650, and then up to 1500 while observing the IAC System Monitor node lights.

Does each node light cycle red and green (never OFF)?

Go to Step 6

Go to Step 5

Turn OFF the ignition switch.
Disconnect the PCM.
Turn ON the ignition switch.
Check the following circuits for an open, short to voltage, or short to ground:

•	IAC A Low.

•	IAC A High.

•	IAC B Low.

•	IAC B High.

If a problem is found, repair as necessary. Refer to Wiring Repairs .

Was a problem found?

Go to Step 11

Go to Step 9

Visually/physically inspect for the following conditions:

•	Throttle body tampering (throttle lever stop screw turned).

•	Check for a possible collapsed air intake duct, restricted air filter element, or foreign objects blocking the air intake system.

•	Remove the IAC valve. Refer to Idle Air Control Valve Replacement .

•	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.

If a problem is found, repair as necessary.

Was a problem found?

Go to Step 11

Go to Step 7

Check for a poor connection at the IAC harness connector.
If a problem is found, repair as necessary. Refer to Intermittents and Poor Connections Diagnosis .

Was a problem found?

Go to Step 11

Go to Step 8

Replace the IAC valve. Refer to Idle Air Control Valve Replacement .

Is action complete?

Go to Step 11

Check for a poor connection at the PCM harness connector.
If a problem is found, repair as necessary. Refer to Intermittents and Poor Connections Diagnosis .

Was a problem found?

Go to Step 11

Go to Step 10

Important:: The replacement PCM must be programmed.

Replace the PCM. Refer to Powertrain Control Module Replacement/Programming .

Is action complete?

Go to Step 11

Re-install the IAC valve and connect components as necessary.
Start the engine.
Turn all accessories OFF (A/C, Rear defroster etc.).
Using a scan tool, command RPM up to 1500, down to 650, and then up to 1500 while monitoring Engine Speed on the scan tool.

Does Engine Speed remain within the specified value of Desired Idle for each RPM command?

± 100 RPM

System OK

Go to Step 2