What Does P256A Mean?
The PCM has detected an open circuit or complete lack of signal from the engine idle speed selector sensor or switch. This input allows the driver to request higher idle speeds for certain conditions like PTO operation or cold weather.
Common Causes
35%
Broken or disconnected wiring to idle speed selector switch
30%
Faulty idle speed selector switch
20%
Corroded or damaged connector terminals
10%
Failed PCM internal circuit for switch input
5%
Blown fuse in switch circuit
Diagnostic Steps
1
Step 1: Visually inspect idle speed selector switch and wiring for obvious damage or disconnection
2
Step 2: Check fuse(s) associated with idle speed control circuit using wiring diagram
3
Step 3: Test switch continuity and resistance with multimeter per manufacturer specifications
4
Step 4: Check voltage supply and ground at switch connector with key on
5
Step 5: If switch and wiring test good, suspect PCM issue and perform voltage drop tests on circuits
Estimated Repair Cost
$75 - $350
Parts + labor, varies by vehicle and location
The PCM has detected an open circuit or complete lack of signal from the engine idle speed selector sensor or switch. This input allows the driver to request higher idle speeds for certain conditions like PTO operation or cold weather.
The most common cause of P256A (Engine Idle Speed Selector Sensor/Switch Circuit/Open) is: Broken or disconnected wiring to idle speed selector switch
Typical repair costs for P256A range from $75 to $350, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Vehicle is safe to drive. Idle speed adjustment feature will be unavailable, which may affect comfort or PTO operation if equipped.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P256A to identify the root cause.
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Quick Info
Category
Powertrain
System
Engine Idle Control
Difficulty
Type
Generic (SAE)
Recommended Tools
OBD2 Scanner
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