P0506 means the engine control module measured idle speed below its target by more than a calibrated margin, typically 100 to 200 rpm, for long enough to count as a fault. P0507 is the opposite (idle too high); P0505 is the general idle control system code. On throttle-by-wire engines the module holds idle by cracking the throttle plate; on older engines, with an idle air control valve beside a closed throttle. P0506 says the module reached the end of that authority and the engine was still slow.
Severity: low to moderate. Can you keep driving? Yes. A low idle rarely damages anything, but it stalls the engine at stops, especially with the A/C on or the wheel turned, and a stall in traffic is the real risk. Have it looked at soon.
The three causes behind almost every case
1. Restricted idle air. Carbon around the throttle plate on a throttle-by-wire engine, or a coked idle air control valve and passage on an older one, limits how much air can get past at the plate's learned closed position. The engine idles slow and the module cannot open the path further without exceeding its learned limits. Cleaning fixes it, and on most vehicles the cleaning has to be followed by an idle or throttle relearn, or the idle will be wrong in the other direction (see P0507 for why).
2. A load the idle strategy cannot overcome. The alternator charging a flat battery, the A/C compressor, the power steering pump at lock, or a transmission dragging with a torque converter or a solenoid problem. If the module has lost the signals that warn it of those loads, it cannot compensate in time: a failed power steering pressure switch or an A/C request signal that does not arrive both show up as low idle under load.
3. A calibration that flags a normal idle. FCA bulletins 18-012-20 (June 2020, 2020 Jeep Wrangler with the 2.0 L turbo, sales code EC1, built on or before June 12, 2020) and 18-013-20 (the 2.0 L eTorque version, built on or before June 15, 2020) list P0506 among the codes corrected by reprogramming the PCM, alongside P0607 and a crankcase ventilation hose code. Later bulletins in 2022 extended similar updates. When the idle sounds and reads normal and the code still sets on one of these vehicles, the fix is software.
Less common causes
A vacuum leak large enough to lean the mixture and make idle unstable · an EGR valve stuck open (usually with its own code) · a PCV valve stuck · an ignition or fuel problem making one cylinder weak · a throttle position sensor misreporting · an engine mount that lets the throttle cable pull on cable-throttle engines · the PCM.
A diagnostic order
- Compare actual idle to desired idle on the scan tool. Both are displayed. Note whether the gap appears only under load (A/C on, wheel turned, in gear).
- Look at the throttle body or idle valve. Carbon around the plate or in the idle passage means clean and relearn.
- Check the loads. Battery and charging (a flat battery loads the alternator hard at idle), A/C clutch engagement, power steering pressure signal, transmission behavior in gear at a stop.
- Check for a vacuum leak with fuel trims: strongly positive long-term trim at idle points at unmetered air.
- Check for a software update for the vehicle if nothing is dirty and nothing is loading the engine.
- Clear and verify through a cold start, a hot idle with the A/C cycling, and a stop in gear with the wheel turned.
Frequently asked questions
Can I drive with a P0506 code?
Yes, but a low idle stalls the engine at stops, and a stall in traffic is the risk. Have it fixed soon, and avoid leaving the A/C on at idle until then if that is when it stalls.
Why does P0506 appear only with the A/C on or the wheel turned?
Because those loads pull idle down and the module normally raises idle a moment before they arrive. If the compressor request or the power steering pressure signal is missing, or the idle path is too restricted to add enough air, the engine sags and the code sets under load only.
Will cleaning the throttle body fix P0506?
Often, but only with the relearn afterwards. The module has learned a throttle position around the carbon; clean it without relearning and the idle will be wrong in the other direction. Run the manufacturer's idle relearn with the scan tool.
How much does it cost to fix P0506?
A throttle body cleaning with relearn is under an hour. An idle air control valve is an inexpensive part. A software update is an hour at a dealer. A power steering switch or a vacuum hose is inexpensive. The module is last on the list.
Related codes
- P0505: idle control system malfunction. P0507: idle speed higher than expected; see P0507.
- P0552 / P0554: power steering pressure signal, one of the load warnings the idle strategy depends on.
- P0171 / P0174: lean codes from a vacuum leak; see P0171 and vacuum leaks.
- P0120 to P0124 / P2135: throttle position sensor codes.
The code number itself tells you the family and the domain; how to read an OBD2 code number explains what each character means.