Is a closed throttle position switch the same thing as a throttle position sensor?

No, though they are often bolted together. The sensor produces a continuously varying voltage that tracks how far the plate has opened. The switch produces only two states — resting or not resting. The module uses the sensor for fuelling and the switch as a trustworthy reference for when the throttle truly is at idle. P0510 is about the switch disagreeing with everything else, which is why a perfectly good sensor can still be present alongside it.

Why won't my cruise control work with P0510 stored?

Cruise control needs an unambiguous answer to the question of whether your foot is on the pedal. The closed throttle contact is one of the inputs that answers it. When the module cannot trust that input, most calibrations simply refuse to hand cruise control authority over the throttle, because taking it in an uncertain state would be unsafe. Fix the switch fault and cruise usually returns without any separate repair.

Can P0510 be caused by a dirty throttle body?

Indirectly, yes. Carbon builds up as a ridge at the edge of the throttle bore, and enough of it can stop the plate from returning all the way to its stop. The plate then rests a degree or two open, the switch lifts off its contact, and the module sees a throttle that is never truly closed. Cleaning the bore and the plate edge, followed by an idle relearn if the vehicle requires one, fixes that version of the fault without replacing anything.

My truck is a diesel — where is this switch?

On most diesel pickups and commercial chassis it is not on the engine. The equivalent part is an idle validation switch built into the accelerator pedal assembly in the cab, where it confirms that the analog pedal signal is honest before the engine accepts a fuelling command. Testing at the throttle body on those vehicles wastes an afternoon — go to the pedal.

OBD-II trouble code

P0510: Closed Throttle Position Switch

A switch — not a sensor — is supposed to tell the module the throttle is at rest, and its on/off state no longer agrees with what the rest of the throttle data says.

Medium severityPowertrainThrottle ControlDrivable short-term

Quick facts

System: Powertrain
Category: Throttle Control
Severity: Medium severity
Drivable: Usually safe to drive short-term
Repair cost range: $80 – $550
DIY difficulty: Intermediate DIY

What does P0510 mean?

P0510 concerns a discrete contact, and that single fact shapes the whole diagnosis. Unlike a throttle position sensor, which sweeps a voltage smoothly as the plate opens, a closed throttle position switch has exactly two states: closed at rest and open the instant the throttle leaves idle. The module uses that clean digital edge as a reference point, and it cross-checks the switch against the analog throttle or pedal signal. When the two disagree — the switch insists the throttle is at rest while the analog signal says it is open, or the reverse — the module cannot trust either one and stores P0510.

Two very different populations of vehicles use this code, and knowing which one you own changes where you look. On older cable-throttle engines, the closed throttle contact is built into the throttle position sensor assembly or bolted beside it, and it exists so the module knows exactly when to enable deceleration fuel cut, when to unlock the torque converter and when idle strategy takes over. On many diesel pickups and commercial chassis, the equivalent part is an idle validation switch riding on the accelerator pedal assembly, whose entire job is to confirm the analog pedal signal is honest before the engine will accept a fuelling command.

Because it is a plausibility fault rather than a hard electrical failure, adjustment is a genuine cause here in a way it is not for most modern codes. Plenty of closed throttle switches mount on slotted holes and can be rotated a few degrees. If somebody cleaned the throttle body, changed a throttle cable, replaced an idle stop screw setting or simply bumped the assembly, the switch can be perfectly healthy and still open a fraction of a degree away from where the module expects. The part is fine; the reference point moved.

The symptoms follow from what the switch enables. Lose it and the engine may not cut fuel on deceleration, so you coast with the idle hanging and burn fuel you should not. Cruise control commonly refuses to set, because a controller that cannot confirm a resting throttle will not take authority. On automatics the torque converter clutch strategy can behave oddly. None of that is dangerous, but it is a nagging, economy-costing fault that also blocks emissions testing while the light is on.

Common causes

Closed throttle position switch out of adjustment on its slotted mounting after throttle body or cable work
Worn contacts inside the switch that no longer make cleanly at rest
Throttle plate not returning fully to its stop because of carbon buildup or a sticking linkage
Idle validation switch failure on diesel pedal assemblies
Open, shorted or chafed wiring between the switch and the module
Corroded switch connector
Throttle position sensor drifted out of range so the analog signal no longer agrees with a healthy switch
Aftermarket throttle body or pedal assembly with a slightly different switch geometry

Symptoms

Check engine light on with P0510 stored
Cruise control will not engage or drops out
Idle hangs on deceleration instead of dropping cleanly
Noticeably worse fuel economy in stop-and-go driving
Harsh or delayed torque converter lockup on automatics
Rough or unstable idle in some applications
Reduced power mode on diesel applications where the idle validation switch is part of the fuelling permission chain

Diagnostic steps

1.Watch the switch state in live data while you slowly open the throttle by hand. It should flip from closed to open within the first few degrees and stay consistent every time you repeat the motion.
2.Compare the switch state against the throttle or pedal position percentage in the same data list. A switch reading closed at 15% throttle, or open at rest, is the disagreement the code is describing.
3.Check the throttle plate actually seats against its stop. Carbon at the edge of the bore, a stiff return spring or a binding cable can hold the plate open just enough to lift the switch.
4.Inspect the switch mounting. If it sits on slotted holes, verify it has not been rotated and reset it to specification before condemning the part.
5.Back-probe the switch signal wire and confirm it toggles cleanly between its two voltage levels with no hesitation or intermediate values.
6.On diesel applications with a pedal-mounted idle validation switch, test the switch at the pedal assembly rather than at the throttle body — the part is not on the engine at all.

Repair cost

$80 – $550

Adjustment alone, when the switch is healthy and simply out of position, is often an hour of diagnostic labor at $80-$160. A standalone closed throttle position switch is inexpensive at $25-$90 in parts, so replacement usually lands at $150-$300. Where the switch is integrated into a throttle position sensor or a complete pedal assembly, expect $250-$550 because you buy the whole unit. Diesel idle validation switches sold as part of a pedal assembly sit at the top of that band.

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DIY vs shop

This is an intermediate DIY job. It usually involves diagnostic steps, specialty parts, and some careful work in tight spaces. If you have the tools and a service manual or trustworthy video for your specific vehicle, it is achievable in a weekend. Otherwise, a competent independent shop will be faster.