System: Powertrain (P-Code)
SAE Standard (Generic)
Family: Idle Speed Selector Switch
Code P256D: Engine Idle Speed Selector Sensor/Switch Circuit High
Diagnostic & Technical Explanation
Code P256D (Engine Idle Speed Selector Sensor/Switch Circuit High) sets when the ECM sees an open, shorted, implausible, or intermittent signal from the driver's idle-speed selector switch or dial, used on work trucks to raise idle RPM for cab heating, battery charging, or auxiliary equipment. Because the selector often lives on an upfitter/body-builder circuit, an incorrectly wired auxiliary harness is a suspect alongside worn selector contacts and a broken wire at the dash connector.
First-listed procedure
Rank #1
Clean idle speed selector switch contacts
Easy DIY
This is the first procedure in the authored
consideration order, not a measured cause likelihood. Execute it only when its prerequisites
and diagnostic findings support it. Its cost and labor estimates (where known), the step-by-step procedure and the
remaining 2 procedure(s) are in the licensed dataset. Ordering context.
Full family: Idle Speed Selector Switch
What this page does not show
This page publishes the fault mechanism and the code index. The licensed dataset adds, for
every one of the 15,886 codes, the full authored repair set (56,729 procedures in total)
with the fields deliberately withheld here:
- Procedures 2..n after the first-listed procedure
- Aftermarket parts cost ranges in USD (
est_parts_cost_min/max_usd)
- Professional labor-hour estimates (
est_labor_hours)
- Step-by-step diagnostic and repair instructions
- Replacement-part mappings and catalog lookups
- 6,637 manufacturer-specific OEM codes across 32 makes ($149 tier)