DTC P0506 Idle Speed Low

Circuit Description

The Idle Air Control valve is a PCM controlled stepper motor located on the throttle body. The stepper motor drives a valve pintle which protrudes into a passage that bypasses the throttle plates. The PCM commands the IAC valve pintle to extend to decrease the idle speed. The bypass air flow is reduced and the idle speed decreases as the pintle approaches its seat. The PCM retracts the IAC valve pintle away from its seat to increase the idle speed. The retracting of the IAC valve pintle allows more air to bypass the throttle plates. One of the PCMs uses for the IAC system is to maintain a desired idle speed. This DTC sets when the PCM detects an engine speed outside of the IAC's range of control.

Conditions for Running the DTC

• DTCs P0101, P0102, P0103, P0107, P0108, P0112, P0113, P0117, P0118, P0125, P0171, P0172, P0174, P0175, P0300, P0401, P0404, P0405, P0443, P0500-P0503, P1441 are not set.
• The engine run time is greater than 60 seconds.
• The engine coolant temperature is greater than 60°C (140°F).
• The intake air temperature is greater than -10°C (14°F).
• The barometric pressure is greater than 65 kPa.
• The ignition voltage is between 9.0 and 17.0 volts
• The vehicle speed is no more than 1 mph (1.6 km/h).

Conditions for Setting the DTC

• The actual idle speed is 100 RPM less than the desired idle speed.
• All of the above conditions are present for 5.0 seconds.

Action Taken When the DTC Sets

• 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.

Conditions for Clearing the MIL/DTC

• The PCM turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
• A last test failed, or current DTC, clears when the diagnostic runs and does not fail.
• A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
• Use a scan tool in order to clear the MIL and the DTC.

Diagnostic Aids

Using Freeze Frame and/or Failure Records data may aid in locating an intermittent condition. If you cannot duplicate the DTC, the information included in the Freeze Frame and/or Failure Records data can aid in determining how many miles since the DTC set. The Fail Counter and Pass Counter can also aid determining how many ignition cycles the diagnostic reported a pass and/or a fail. Operate the vehicle within the same freeze frame conditions (RPM, load, vehicle speed, temperature etc.) that you observed. This will isolate when the DTC failed. For an intermittent, refer to Symptoms .

Test Description

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

2. This test determines whether or not the engine can achieve the commanded RPM, and if not, whether the RPM is too high or too low.

Step	Action	Value(s)	Yes	No
1	Did you perform the Powertrain On-Board Diagnostic (OBD) System Check?	--	Go to Step 2	Go to A Powertrain On Board Diagnostic (OBD) System Check
2	Important If there are any MAF/MAP DTCs set, go to the appropriate diagnostic table. Idle the engine. Command the engine speed up to 1500 RPM, down to 500 RPM, up to 1500 RPM, and then EXIT using the scan tool. Does the engine speed correspond, within 100 RPM, with each command?	--	Go to Diagnostic Aids	Go to Step 3
3	Is the engine RPM greater than 100 RPM above Desired RPM?	--	Go to Step 4	Go to Step 5
4	Inspect for the following conditions: Vacuum leaks. Throttle plates not closing properly. A faulty PCV valve. If you find a condition, repair as necessary. Did you find and correct the condition?	--	Go to Step 11	Go to Step 6
5	Inspect for the following conditions: Excessive deposits in the throttle body. Parasitic load on the engine (i.e.: transmission condition etc.). If you find a condition, repair as necessary. Did you find and correct the condition?	--	Go to Step 11	Go to Step 6
6	Start and idle the engine Disconnect the IAC harness connector and install the appropriate IAC node light from kit J 37027-A. Command the RPM up to 1500, down to 500 and up to 1,500 using the scan tool while observing the node light. Does both of the LEDs on the node light cycle red and green, but never OFF?	--	Go to Step 7	Go to Step 8
7	Important: During the following test it is possible to overextend the IAC valve pintle until it falls out of the worm drive. If this occurs, manually screw the pintle shaft into the worm drive about 2 turns to get it started, align the keyways on the shaft with the keys in the housing and gradually retract the pintle using the IAC driver tool. Turn OFF the ignition. Remove the IAC valve. Connect the IAC valve to the IAC Driver tool from kit J 37027-A. Hold the IAC valve with a finger over the pintle in case it is over extended. Using the driver tool retract and extend the pintle. Does the pintle move steadily with each flash of the IAC driver light?	--	Go to Step 9	Go to Step 10
8	Inspect for the following conditions: Faulty connections. Refer to Intermittents and Poor Connections Diagnosis in Wiring Systems. Open circuit. Refer to Testing for Continuity in Wiring Systems. Short to ground. Refer to Testing for Short to Ground in Wiring Systems. Short to B+. If you find a condition, repair as necessary. Refer to Wiring Repairs in Wiring Systems. Did you find and correct the condition?	--	Go to Step 13	Go to Step 11
9	Inspect the IAC passages. Is the action complete?	--	Go to Step 13	--
10	Replace the IAC valve. Refer to IAC Valve Replacement Is the action complete?	--	Go to Step 13	--
11	Inspect for poor connections at the PCM. Refer to Intermittents and Poor Connections Diagnosis in Wiring Systems. If you find a poor connection, repair as necessary. Refer to Repairing Connector Terminals in Wiring Systems. Did you find and correct the condition?	--	Go to Step 13	Go to Step 12
12	Important: Program the replacement PCM. Refer to PCM Replacement/Programming . Replace the PCM. Is the action complete?	--	Go to Step 13	--
13	Select the Diagnostic Trouble Code (DTC) option and the Clear DTC Information option using the scan tool. Idle the engine at the normal operating temperature. Select the Diagnostic Trouble Code (DTC) option and the Specific DTC option, then enter the DTC number using the scan tool. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text, if applicable. Does the scan tool indicate that this test ran and passed?	--	Go to Step 14	Go to Step 2
14	Select the Capture Info option and the Review Info option using the scan tool. Does the scan tool display any DTCs that you have not diagnosed?	--	Go to the applicable DTC table	System OK