What it means
A general electrical fault on the "C" channel of the throttle or pedal position sensor. Drive-by-wire pedals carry two or three redundant tracks; "C" is the third channel.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
The pedal or throttle position sensor assembly can use several separate tracks to give the control module redundant position readings; this code refers to circuit D. P2120 sets when the module detects a general electrical fault in that D circuit, such as a failed track or an open signal wire, rather than a defined low or high reading.
Common causes
Most likely first.
- Pedal sensor track C failed
- Signal wire open
Symptoms
- Check engine light on
- Reduced throttle response, possible limp mode
- Hesitation or surging
- Idle too high or too low
How to diagnose it
- Record freeze-frame data and related pedal or throttle codes, then view the available position-sensor channels on a scan tool to identify whether circuit D is missing or erratic.
- With the ignition off, inspect the pedal or throttle position sensor D connector and wiring for loose pins, corrosion, abrasion, or a broken signal wire.
- Check the circuit D signal, reference supply, and ground using the vehicle wiring information and compare results with the manufacturer's specification.
- Move the harness gently while monitoring circuit D data to reveal an intermittent open or poor connection.
- If wiring and supplies test correctly, test the position sensor assembly and its D track according to vehicle-specific service information.
Common fixes
- Reconnect and secure a loose circuit D connector.
- Repair an open or damaged D signal wire.
- Clean or replace corroded terminals and restore the specified sensor supply or ground.
- Replace the pedal or throttle position sensor assembly if its D track fails testing.
Can I keep driving?
The control module may limit throttle response or enter a protective mode, even if limp mode is not currently active. Avoid busy roads and overtaking if acceleration is inconsistent, and stop driving if you cannot control the vehicle's response reliably.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.