DTC P0506 Idle Speed Low. Buick GL7 (Export) 2000

For 1990-2009 cars

### Circuit Description

The powertrain control module (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 2 coils. The PCM applies current to the IAC coils in pulses to extend the IAC pintle into a passage in the throttle body and decrease the air flow. The PCM reverses the current to retract the pintle, increasing the air flow. This method allows highly accurate control of the idle speed and a quick response to changes in the engine load. If the PCM detects a condition where too low an idle speed is present, and the PCM is unable to adjust the idle speed by increasing the IAC counts, DTC P0506 will set.

### Conditions for Running the DTC

• | No active TP, ECT, MAP, IAT, MAF, CKP, EVAP, misfire, EGR, VSS, fuel trim, or injector circuit DTCs are active.

• | The engine coolant temperature is more than 70°C (158°F).

• | The engine has been running for at least 2 minutes.

• | The system voltage is between 9.0-18.0 volts.

• | The vehicle speed is less than 4.8 km/h (3 mph).

• | The intake air temperature (IAT) is more than -18°C (0°F).

• | The throttle angle is less than 1.5 percent.

• | The barometric pressure (BARO) is more than 65 kPa.

### Conditions for Setting the DTC

• | The engine speed is more than 175 RPM lower than the Desired Idle.

• | The above condition is present for more 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/Failure Records data.

### Conditions for Clearing the MIL/DTC

• | 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.

### Diagnostic Aids

Inspect for the following conditions:

• | A poor connection at the PCM or the IAC valve. Inspect harness connectors for the following conditions:

- | Backed-out terminals

- | Improper mating

- | Broken locks

- | Improperly formed or damaged terminals

- | Poor terminal-to-wire connection

• | Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

• | A damaged harness. Inspect the wiring harness for damage. Refer to Wiring Repairs in Wiring Systems.

• | A restricted air intake system. Inspect for a collapsed air intake duct, a restricted air filter element, or any foreign objects blocking the air intake system.

• | The throttle body. Inspect for objects blocking the IAC passage or the throttle bore, any excessive deposits in the IAC passage, on the IAC pintle, in the throttle bore, or on the throttle plate.

• | A large vacuum leak. Inspect for a condition that causes a large vacuum leak, such as a incorrectly installed or faulty PCV valve or the brake booster hose disconnected. Refer to Symptoms .

If the DTC cannot be duplicated and is determined to be intermittent, reviewing the Failure Records can be useful in determining when the DTC was last set. Also refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

### Test Description

The number below refers to the step number on the diagnostic table.

1. This vehicle is equipped with a PCM which utilizes an electrically erasable programmable read-only memory (EEPROM). If the PCM is replaced, the new PCM must be programmed.

Step | Action | Values | Yes | No
--- | --- | --- | --- | ---
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | Go to Step 2 | Go to Powertrain On Board Diagnostic (OBD) System Check
2 | Are any other DTCs set? | -- | Go to the applicable DTC table | Go to Step 3

3

1. Start the engine.
2. Turn OFF all accessories.
3. Using a scan tool, command the RPM up to 1500, down to 650, and then up to 1500 while monitoring the Engine Speed on the scan tool.

Does the engine speed remain within the specified range of the Desired Idle for each RPM command?

±50 RPM

Go to Diagnostic Aids

Go to Step 4

4

1. Disconnect the IAC.
2. Install a J 37027-A system motor analyzer to IAC harness connector.
3. Start the engine.
4. With a scan tool command the RPM up to 1500, down to 650, and then up to 1500 while observing the node lamp.

Does each node lamp cycle red and green but never off?

--

Go to Step 6

Go to Step 5

5

1. Test the following circuits for an open, a short to voltage, or a short to ground:

• | The IAC A low circuit

• | The IAC A high circuit

• | The IAC B low circuit

• | The IAC B high circuit

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

Did you find and correct the condition?

--

Go to Step 11

Go to Step 9

6

Visually and physically inspect for the following conditions:

• | Any throttle body tampering or the throttle lever stop screw turned

• | A restricted air intake system. Inspect for a possible collapsed air intake duct, a restricted air filter element, or any foreign objects blocking the air intake system.

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

• | Inspect for objects blocking the IAC passage or the 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.

Does any of the above require a repair?

--

Go to appropriate section for on-vehicle service

Go to Step 7

7

1. Inspect for a poor connection at the IAC harness connector.
2. If a problem is found, replace the faulty terminals as necessary. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 11

Go to Step 8

8 | Replace the IAC valve. Refer to Idle Air Control Valve Replacement . Did you complete the replacement? | -- | Go to Step 11 | --

9

1. Inspect for a poor connection at the PCM harness connector.
2. If a problem is found, replace the faulty terminals as necessary. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 11

Go to Step 10

10 | Important: : The replacement PCM must be programmed. Replace the PCM. Refer to Powertrain Control Module Replacement/Programming . Did you complete the replacement? | -- | Go to Step 11 | --

11

1. Reinstall and connect the components as necessary.
2. Start the engine.
3. Turn OFF all of the accessories.
4. Using a scan tool, command the RPM up to 1500, down to 650, and then up to 1500 while monitoring the Engine Speed on the scan tool.

Does the engine speed remain within the specified range of the Desired Idle for each RPM command?

±50 RPM

System OK

Go to Step 2