P2621: Throttle Position Output Circuit Low
What to do
The engine responds normally to the pedal while the gearbox behaves as though you are never using it — changing up far too early, refusing to hold a gear when you accelerate, and giving no kickdown.
Say exactly that, because it points at the message rather than at the gearbox. The transmission is being told the throttle is shut, and acting sensibly on wrong information. Neither the throttle body nor the pedal is at fault — the engine's response proves that — so a transmission overhaul or a new throttle body would change nothing. The wiring between the two modules is where to look.
What this code means
The throttle position output circuit reads below its valid range — a short to ground, or an input at the receiving end holding it down.
A signal stuck at the bottom of its range is not read as missing by the module receiving it. It is read as a closed throttle, which is a perfectly plausible value. That produces a transmission convinced the driver is coasting, whatever the driver is actually doing: upshifts arrive absurdly early, the gearbox refuses to hold a gear under acceleration, and there is no kickdown at all.
That is worth separating from P2620, where the signal is absent and the receiving module usually knows it is absent and adopts a default. A wrong-but-believable value is handled worse than no value, which is why this variant tends to produce the more dramatic complaint.
The reasoning about which parts are exonerated is at P2620 and holds here unchanged.
Likely causes
Start here
- Wiring shorted to ground · moderate
- Damaged wiring harness · moderate
- Faulty receiving module input · specialist
Less common
- Corroded or loose connector · easy
- Faulty transmission control module · specialist
Symptoms
Components involved
Information, not instruction
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Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
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What makes one worth reading:
- The car — make, model, year and engine. The same fault behaves differently on each.
- What you measured, not only what you replaced.
- What actually fixed it — or that nothing did, which is worth knowing too.
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