What it means
The idle-speed selector input is open. On commercial vehicles this switch lets the operator pick a fast-idle setpoint (for example to keep auxiliary loads supplied). With the input broken, the ECM cannot apply an operator-selected idle speed.
At a glance
- Usually lights the check-engine light
How it works
On vehicles equipped with it, the engine idle speed selector switch lets an operator choose a fast-idle setting, often to support auxiliary loads. The engine control module monitors the selector input and sets this open-circuit code when it cannot detect a usable electrical connection, so it may not apply the selected idle speed.
Common causes
Most likely first.
- Open wire or unplugged switch
- Pin pushed back out of connector body
- Cracked solder joint inside the module or sensor
Symptoms
- Check engine light on
- Idle speed too high, too low, or unstable
- Possible stalling at idle or after cold start
How to diagnose it
- Save freeze-frame data and check the selector input on a scan tool while moving the switch through its available positions.
- Inspect the idle speed selector and its connector for disconnection, damaged wiring, corrosion, or a pin pushed back into the connector.
- Check continuity through the switch and its wiring with the circuit powered down, following the vehicle wiring diagram.
- Verify the selector circuit's supply and ground, where fitted, against the manufacturer's specification.
- If the switch and harness pass, inspect the module or sensor connection for an internal open using the manufacturer's diagnostic procedure.
Common fixes
- Reconnect a disconnected selector switch or repair its open wire.
- Reseat a pushed-back terminal and secure the connector.
- Repair corroded or damaged switch wiring.
- Replace a selector switch that has an open internal contact.
- Repair an internal module or sensor connection only after circuit testing confirms the fault.
Can I keep driving?
If the vehicle idles steadily and drives normally, ordinary short trips may be possible, but do not rely on the operator-selected fast idle for auxiliary equipment. Avoid operating equipment that depends on a stable elevated idle until the selector works.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.