P2121: The accelerator pedal or throttle position sensor "D" signal does not make sense compared with the other throttle signals

Throttle/pedal position sensor D range/performance

Severity: Inspect soon

The computer usually limits engine power or drops into limp mode when it distrusts the pedal or throttle signals. PartsAvatar rates the code high severity and an owner reports losing throttle input in traffic, so get it checked soon.

It gets more serious if:

Stop: Stop somewhere safe and have the vehicle towed if power drops suddenly, the engine falls to idle or stalls while moving. A throttle that will not respond can leave you unable to keep up with traffic.

Source: how we rate severity

P2121 in short

P2121 means the computer sees a throttle or accelerator pedal sensor signal that does not match the others. The usual causes are a faulty pedal or throttle sensor, damaged wiring or connectors, or a failing throttle motor. The engine may go into limp mode, so get it checked soon.

Most modern cars have no throttle cable. The pedal has position sensors, and the computer opens the throttle with a small motor, checking the position sensors on both ends. P2121 sets when the signal from sensor "D" is outside the expected range or does not agree with the other sensors.

Which sensor is "D" differs by maker, so a service manual for your vehicle matters here. Wiring and connectors, the pedal assembly and the throttle body are the places to look.

When the computer cannot trust the signals it protects the engine: reduced power, a throttle that lags or a limp-mode speed cap. An owner of a 2019 Ram 2500 told NHTSA the truck repeatedly lost throttle input in traffic with P2121 stored and the dealer had not found the cause after three visits.

Most likely causes

These are general causes for this code across vehicles. None is specific to one make or model.

Cause 1: Accelerator pedal position sensor
Common general cause
Why it ranks here
Both TroubleCodes.net and PartsAvatar list a faulty pedal or throttle position sensor, and TroubleCodes.net says the pedal assembly is normally replaced as one unit.
What would change this
Rises if pedal position values on a scan tool jump, drop out or disagree as the pedal moves. Falls if the pedal signals sweep smoothly and agree.
How to test the accelerator pedal position sensor
Cause 2: Wiring or connector fault at the pedal or throttle
Common general cause
Why it ranks here
Both sources start with corroded, shorted or loose wiring and connectors. A 2008 Ram 3500 owner told NHTSA that the dealer re-crimped the pedal sensor plug and the engine-bay connector before the light came back.
What would change this
Rises if wiggling the connector changes the readings or the code is intermittent. Falls if the wiring tests good.
Cause 3: Throttle body or throttle motor
Common general cause
Why it ranks here
PartsAvatar and TroubleCodes.net both list the throttle actuator motor and throttle position sensors as causes.
What would change this
Rises if the throttle does not follow the commanded position on a scan tool. Falls if it tracks the command closely.
How to test the electronic throttle body
Cause 4: Loose control-module ground or a failing computer (rare)
Possible — needs testing
Why it ranks here
PartsAvatar lists a loose control-module ground strap or broken ground wire, and TroubleCodes.net lists the PCM as rare. They rank last because they are less common.
What would change this
Rises if everything else tests good and other unrelated codes are stored. Falls if the pedal or throttle is found at fault.
How to test the engine control module (ecm / pcm)

What to test first

Start at step 1. Each result tells you what it means and where to go next.

Step 1: Read all codes and freeze-frame data, then watch the pedal position sensor signals on a scan tool as you press the pedal slowly.
Low riskTool: scan tool with live data
- IfPedal signals jump, drop out or disagree with each other
  It meansThe pedal sensor or its wiring is the suspect.
  Go to step 2
- IfPedal signals are smooth and agree, but the throttle does not follow
  It meansLook at the throttle body.
  Points to: Throttle body or throttle motor
Step 2: With the ignition off, check the pedal and throttle connectors for water, corrosion or a loose fit, and gently wiggle them while watching the live data.
Low risk
- IfWiggling a connector changes the readings or you find corrosion
  It meansA wiring or connector fault is likely.
  Points to: Wiring or connector fault at the pedal or throttle
- IfConnectors look fine and the pedal readings are still bad
  It meansThe pedal sensor itself is likely.
  Points to: Accelerator pedal position sensor
- IfPedal and connectors are fine and the control module loses power or ground
  It meansHave the grounds and computer checked.
  Points to: Loose control-module ground or a failing computer (rare)

Symptoms

Check engine light or an electronic throttle warning light
Sluggish or delayed throttle response
Reduced power or limp mode with a low speed cap
Sudden loss of throttle response, or the engine drops to idle or stalls Gets more serious: stop and have it checked.

Compare with: Check engine light with loss of power

How to fix

Step 1: With the ignition off, check the accelerator pedal and throttle connectors are fully seated and free of corrosion.
Step 2: Ask a dealer whether your VIN has a bulletin or software update for throttle or pedal codes.

Parts and cost context

Accelerator pedal position sensor:The pedal sensor is usually part of the pedal assembly and is replaced as one piece. Labour varies; get a quote.
Electronic throttle body:Replace only after the pedal, wiring and connectors are ruled out.

Labor varies by vehicle and shop; get a quote before you approve a repair.

Compare used part prices on PartPriceGuide

On your vehicle

Ram

2019 · 2500
Possible — needs testing
A 2019 Ram 2500 owner reports intermittent loss of throttle input with the check engine and electronic throttle control lights and P2121 stored; three dealer visits had not found the cause. This is one complaint, not a bulletin.

Dodge

2008 · Ram
Possible — needs testing
A 2008 Ram 3500 owner reports a flashing ETC light with limp mode; the dealer replaced the pedal, re-crimped the pedal sensor plug and the engine-bay connector. This is one complaint, not a bulletin.

All Electronic throttle and accelerator pedal codes

P2121 questions

What does the D mean in P2121?

It names one of several throttle or pedal sensor circuits. Which one is D differs by maker, so check a service manual for your vehicle.

Is it safe to drive with P2121?

Be careful. The car may drop into limp mode or lose throttle response, which is dangerous in traffic. Get it checked soon.

Sources and review

P2121 Throttle Position Sensor D Circuit Range/Performance — PartsAvatar
NHTSA complaint ODI 11464922 — NHTSA Office of Defects Investigation
P2121 trouble code summary — TroubleCodes.net
NHTSA complaint ODI 10745500 — NHTSA Office of Defects Investigation

Last reviewed: October 15, 2026
Written by: Saurabh K.
Editorial review: Pending
Technician review: Technician review pending

This page explains what a code usually means; it is not a substitute for a professional inspection. How we source and review · Report an error

Severity: Inspect soon

Most likely causes

Cause 1: Accelerator pedal position sensor

Cause 2: Wiring or connector fault at the pedal or throttle

Cause 3: Throttle body or throttle motor

Cause 4: Loose control-module ground or a failing computer (rare)

What to test first

Step 1: Read all codes and freeze-frame data, then watch the pedal position sensor signals on a scan tool as you press the pedal slowly.

Step 2: With the ignition off, check the pedal and throttle connectors for water, corrosion or a loose fit, and gently wiggle them while watching the live data.