P256A
- Powertrain
- Manufacturer-specific
Diagnose soon
Usually safe to drive short distances, but the fault will not clear itself and can worsen or fail an emissions test.
Engine Idle Speed Selector Sensor/Switch Circuit/Open
This code is in our catalogue but has not yet been through editorial review, so the guidance below is limited to what our structured data supports. We publish deeper diagnostic content only after a code has been reviewed — here is why.
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.
A trouble code records what a control module measured. It does not identify which part failed. Test before replacing anything.
- Safe to drive
- Usually safe to drive short distances, but the fault will not clear itself and can worsen or fail an emissions test.
- Urgency
- Diagnose soon
- Will it pass emissions
- Not affected
- Check engine light
- Solid
- Idle speed too high, too low, or unstable
- Possible stalling at idle or after cold start
Many vehicles show no symptom at all beyond the warning light. The absence of a symptom does not mean the fault is not real.
| # | Cause | How often | Component |
|---|---|---|---|
| 1 | Open wire or unplugged switch | Very common | — |
| 2 | Pin pushed back out of connector body | Occasional | — |
| 3 | Cracked solder joint inside the module or sensor | Occasional | — |
Ordering reflects how often each cause is responsible in general, not a probability for your vehicle. Confirm by testing.
- Idle Speed Selector Switch
- Wiring Harness
- Definition
- Generic code set (SAE J2012 / ISO 15031-6) via the OBDexopen database, dedicated to the public domain under CC0-1.0.
- Diagnostic guidance
- Written and reviewed in-house. See our editorial policy.
- Review status
- Awaiting review
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