P256B code meaning
Engine Idle Speed Selector Sensor/Switch Range/Performance
What P256B means
P256B means the idle speed selector delivers a value that is electrically valid but makes no sense in context. The controller may, for instance, see a raised-idle request with the truck in motion, a position that does not exist, or a request that conflicts with an active PTO mode; Ram's 2012 chassis cab guide states that remote PTO outranks the Idle Up function, so the two inputs have a defined order the software can check. CARB defines a rationality diagnostic as comparing an input within its normal range with all other available information. No manufacturer publishes P256B. Likely causes are a sticking or misadjusted switch, aftermarket idle controls wired into the same circuit, or a configuration change. The idle request is usually ignored.
P256B at a glance
- Check engine lightUsually not
- Emissions testNot an emissions code
- Limp modeNot expected
- Repair difficultyMedium, DIY possible
- Typical labor0.5 to 2 hours
- Clears after repairWhen cleared with a scanner
Symptoms of P256B
- Raised idle request ignored
- Idle selection works only sometimes
Common causes of P256B
- Most likelySticking or misadjusted idle selector
- PossibleAftermarket idle control wired into the same circuit
- Less likelyIdle or PTO configuration changed without matching hardware
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Idle speed selector switch
What each part of P256B means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 2 | Generic code (second SAE range): it means the same on every make. |
| 5 | Area: vehicle speed, idle control and auxiliary inputs. |
| 6B | The exact fault in that area. |
What to do next
- Note P256B and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P256B
What does P256B mean?
P256B means "Engine Idle Speed Selector Sensor/Switch Range/Performance". P256B means the idle speed selector delivers a value that is electrically valid but makes no sense in context. It is a generic code, so it means the same on every make.
Is it safe to drive with P256B?
P256B does not normally turn on the check engine light by itself. Watch for the symptoms above and have it checked soon.
Will P256B fail an emissions test?
P256B is not an emissions code, so on its own it usually does not fail an emissions test. Other stored codes or a lit check engine light still can.
How hard is P256B to fix?
Difficulty: medium. A typical repair takes 0.5 to 2 hours of work. A careful DIY repair is possible with basic tools and a scanner.
Will P256B clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.