What Does P256B Mean?
The idle speed selector sensor/switch signal is present but outside expected parameters or behaving inconsistently. The PCM detects a signal that doesn't match known switch positions or changes unexpectedly.
Common Causes
40%
Idle speed selector switch worn or internally damaged
25%
High resistance in wiring or connectors causing voltage drop
20%
Intermittent short to ground or power in switch circuit
10%
Incorrect switch installed or switch out of calibration
5%
PCM software calibration issue
Diagnostic Steps
1
Step 1: Monitor switch signal voltage in live data while cycling through all switch positions
2
Step 2: Compare voltage readings to manufacturer specifications for each position
3
Step 3: Perform resistance test on switch in all positions with multimeter
4
Step 4: Check for voltage drops in wiring by back-probing connectors under load
5
Step 5: If readings are inconsistent, wiggle harness to check for intermittent connections
Estimated Repair Cost
$100 - $400
Parts + labor, varies by vehicle and location
The idle speed selector sensor/switch signal is present but outside expected parameters or behaving inconsistently. The PCM detects a signal that doesn't match known switch positions or changes unexpectedly.
The most common cause of P256B (Engine Idle Speed Selector Sensor/Switch Range/Performance) is: Idle speed selector switch worn or internally damaged
Typical repair costs for P256B range from $100 to $400, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Safe to drive. Incorrect idle speed selection may occur, potentially causing rough idle or stalling in certain conditions.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P256B to identify the root cause.
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Quick Info
Category
Powertrain
System
Engine Idle Control
Difficulty
Type
Generic (SAE)
Recommended Tools
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