P0506
P0506 Idle Speed RPM Lower Than Desired Idle Speed
Circuit Description
The powertrain control module (PCM)/engine control module (ECM) controls the air entering into the engine with an Idle Air Control (IAC) Valve. To increase the idle rpm. the PCM/ECM commands the pintle inside the IAC valve away from the throttle body seat. This allows more air to bypass through the throttle blade. To decrease the rpm the PCM/ECM commands the pintle towards the throttle body seat. This reduces the amount of air bypassing the throttle blade. A scan tool will read the IAC valve pintle position in counts. The higher the counts, the more air that is allowed to bypass the throttle blade. This Diagnostic Trouble Code (DTC) determines if a low idle condition exists as defined as 100 rpm below the desired idle rpm.
Conditions for Setting the DTC
- No OBD II intrusive tests active.
- DTC(s) P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0131, P0132, P0133, P0134, P0137, P0138, P0140, P0141, P0171, P0172, P0201, P0202, P0203, P0204, P0300, P0336, P0337, P0341, P0342, P0351, P0352, P0402, P0404, P0405, P0406, P0502, P1130, P1133, P1134, P1171, P1404, P1441, P1627 not set.
- Idle engine speed error is greater than 100 rpm for 10 seconds.
- Engine Coolant Temperature (ECT) is greater than 108.5 °F (42.5 °C).
- Barometric Pressure (BARO) is greater than 72.3 kPa.
- Ignition voltage is between 11 and 16 volts.
- Engine has been running more than 10 seconds.
- The Intake Air Temperature (IAT) is greater than 4.25 °C.
- The Manifold Absolute Pressure (MAP) is less than 60 kPa.
- All of the above must be met for greater than 5 seconds.
Action Taken When the DTC Sets
- The Malfunction Indicator Lamp (MIL) will illuminate.
- The PCM/ECM will record operating conditions at the time the diagnostic fails. This information will be stored in the Freeze Frame and Failure Records buffers.
- A history DTC is stored.
Conditions for Clearing the MIL/DTC
- The MIL will turn off after three consecutive ignition cycles in which the diagnostic runs without a fault.
- A history DTC will clear after 40 consecutive warm up cycles without a fault.
- DTC(s) can be cleared by using the scan tool.
Diagnostic Aids
Inspect the IAC valve electrical connection for proper mating.
Inspect the wiring harness for damage.
Inspect throttle stop screw for signs of tampering.
Inspect throttle linkage for signs of binding or excessive wear.
A slow, or unstable idle may be caused by one of the following conditions:
- Fuel system too rich or too lean.
- Foreign material in the throttle body bore or in the air induction system.
- A leaking or restricted intake manifold.
- Excessive engine overloading. Check for seized pulleys, pumps, or motors on the accessory drive,
- Overweight engine oil.
Step 1 - 2:
Step 3 - 14:
Step 15 - 16:
Test Description
Number(s) below refer to the step number(s) on the Diagnostic Table
1. The On-Board Diagnostic (OBD II) System Check prompts the technician to complete some basic checks and store the freeze frame and failure records data on the scan tool if applicable. This creates an electronic copy of the data taken when the malfunction occurred. The information is then stored on the scan tool for later reference.
2. A normally operating IAC system will be able to be extended and retracted by a scan tool and change the engine idle rpm. Valve movement is verified by an engine rpm change.
3. If the scan tool was able to command the IAC valve smoothly, a malfunction may still exist internally within the IAC valve. This can be checked by checking the AC valves internal resistance.
5. The IAC circuits always have ground or voltage signals on them in pairs. If the test light illuminates on more or less than 2 terminals, 1 of the circuits is shorted to voltage or open.
6. The IAC circuits always have ground or voltage signals on them in pairs. If the test light illuminates on more or less than 2 terminals, 1 of the circuits is shorted to ground or open
8. The IAC circuits are constantly switched between ground and voltage so the test light should blink on all circuits when connected to ground.
10. Any circuitry, that is suspected as causing the intermittent complaint, should be thoroughly checked for backed-out terminals, improper mating, broke locks, improperly formed or damaged terminals, poor terminal-to-wiring connections or physical damage to the wiring harness.
12. A test light that remains ON constantly indicates that the circuit is shorted to voltage.
14. The replacement PCM/ECM must be reprogrammed. Refer to the latest Techline procedure for PCM/ECM reprogramming.
16. If no malfunctions have been found at this point and no additional DTCs were set, refer to "Diagnostic Aids" for additional checks and information.