The P256C: Engine Idle Speed Selector Sensor/Switch Circuit Low indicates that the voltage or signal in the engine idle speed selector sensor or switch circuit is below the expected level. This issue could be caused by a faulty sensor, an open or short circuit, or problems with wiring or connectors. Resolving this issue is crucial for maintaining proper idle speed control, which ensures smooth engine operation.
P256C – Quick Overview
| Code | Information |
|---|---|
| Meaning | P256C: Engine Idle Speed Selector Sensor/Switch Circuit Low |
| Is it serious? | Yes, a low signal in this circuit can lead to improper idle control, resulting in engine stalling, irregular idling, or poor engine performance. |
| Possible causes | – Low voltage or signal in the engine idle speed selector sensor/switch circuit – Faulty engine idle speed selector sensor/switch – Wiring or connector issues |
| How to diagnose? | – Measure the voltage in the engine idle speed selector sensor/switch circuit – Inspect and test the engine idle speed selector sensor/switch – Check wiring and connectors – Replace faulty components if needed |
P256C Meaning
The P256C: Engine Idle Speed Selector Sensor/Switch Circuit Low code indicates that the sensor or switch used to select and manage the engine idle speed is experiencing a lower-than-expected voltage or signal. This may happen due to faulty wiring, a damaged sensor, or poor electrical connections, which prevents the ECU from accurately controlling the engine idle speed.
Step-by-step diagnostic guide
| Action | Description | Tools Needed |
|---|---|---|
| Check for Other Related Codes | Use an OBD-II scanner to determine if there are other related fault codes present. Other codes may help narrow down additional issues affecting the idle speed control system. | OBD-II Scanner |
| Measure Voltage in the Sensor Circuit | Use a multimeter to measure the voltage of the engine idle speed selector sensor/switch circuit. Compare the voltage reading to manufacturer specifications to determine if the signal is below acceptable levels. | Multimeter |
| Inspect the Idle Speed Selector Sensor/Switch | Visually inspect the sensor or switch for any signs of damage, such as cracks, corrosion, or loose connections. Ensure that the sensor is properly installed and not obstructed. | Flashlight, Safety Gloves |
| Test the Idle Speed Selector Sensor/Switch | Use a diagnostic tool to monitor the output signal of the sensor. Check if the sensor provides a consistent signal within the expected range under varying conditions. | Diagnostic Tool, Multimeter |
| Check Wiring and Connectors | Inspect all wiring and connectors leading to and from the sensor or switch. Look for damaged wires, loose or corroded connectors, or signs of short circuits that could cause the signal to be low. | Flashlight, Multimeter |
| Repair or Replace Faulty Wiring/Connectors | If damaged wiring or connectors are found, repair or replace them to restore proper signal strength. Ensure that all connections are tight and clean to prevent electrical resistance issues. | Basic Tools, Replacement Parts |
| Replace Faulty Idle Speed Selector Sensor/Switch | If the sensor or switch is found to be faulty, replace it with a new component. Make sure that the replacement part is compatible with the system and correctly calibrated if necessary. | Replacement Idle Speed Selector Sensor/Switch |
| Clear the Code and Test Drive | After completing repairs, use an OBD-II scanner to clear the fault code. Start the vehicle and let it idle, observing the performance to ensure that the idle control is functioning properly. Perform a test drive if needed to confirm the issue is resolved. | OBD-II Scanner, Vehicle Owner’s Manual |
| Recheck for Codes | Re-scan the vehicle after the test drive to verify that the P256C code has been cleared. If the code persists, additional diagnostics will be required to determine any other underlying issues. | OBD-II Scanner |
Free PDF: How to choose OBD2 scanner
I’ve made you a free PDF to choose the OBD2 scanner in 5 minutes.
✅ Which OBD2 scanner is best?
✅ Which type should you get (DIY, Pro, Hobby)
✅ What is the best scanner for the exact brand/feature (e.g best for BMW)
✅ How to get a Bi-Directional tool for as cheap as $40
✅ Discount coupons for scanners
PDF is 100% free and it is designed to help you pick a scanner in less than a few minutes! Not a boring 50-page guide.
Just tell me where to send it.
Hi, I am Juraj “Yuri” Lukacko. I got frustrated by unhelpful and scammy mechanics, so I decided to learn everything about car diagnostics myself. I test dozens of new car diagnostic tools every month along with learning new strategies to fix and customize cars. About Juraj Lukacko (Yuri)