P2621 Throttle Position Output Circuit Low

P2621 flags the throttle position output line as shorted to ground or reading below its permitted voltage band. A receiving module such as a transmission controller would then see a value that looks like a fully closed throttle all the time. No carmaker publishes a code-specific description with limits; the CARB requirement for output monitoring and GM's output-driver tests on the crank signal (0.5 ohm toward ground counted as a short, 40 failures in 50 samples) illustrate the usual method, but they are an analogy, not a documented P2621 strategy. Check the wire between the two modules for chafing against body ground and the connectors for corrosion before suspecting either controller. Compared with P2620 (open line) and P2622 (short to supply), the receiver here gets a steady low level.

Likely causes

Symptoms

• Stored code in the engine module
• Receiver behaves as if the throttle were always closed (late or odd shifts)

Repair estimate

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

Related codes

References: law.cornell.edu, gsi.ext.gm.com.