P2120 Code: Accelerator Pedal Position Sensor D Circuit
The PCM lost a usable signal from the main gas pedal sensor, often only for a moment.
At a glance
Severity: Moderate
- Meaning
- Accelerator Pedal Position Sensor D Circuit
- System
- Speed & Idle Control · Powertrain
- Safe to drive?
- With caution
- Typical repair cost
- $80–$500
- DIY difficulty
- Moderate
Sensor D is the primary track in the electronic gas pedal; its partner E is used as a cross-check. P2120 is the general circuit code: the PCM saw the D signal drop out, jump outside its valid window or stop responding, without the fault fitting neatly into the separate low (P2122) or high (P2123) codes. Some makes use P2120 for any D circuit failure, others only for intermittent ones, so the stored freeze frame matters. At rest D typically reads somewhere around 0.4–1.0 V and climbs smoothly to about 4 V or more at the floor. Because the fault is often brief, the connector on top of the pedal module and the harness between pedal and PCM are the first places to look, ahead of the pedal itself. While D is out, the PCM drives on sensor E alone with throttle opening and response deliberately limited.
Can I keep driving? The car usually still moves but accelerates slowly, and it may fall to idle if the second sensor also drops out. Drive gently to a shop and avoid situations where you need full power.
How to read P2120
- P Powertrain
- 2 Generic (SAE)
- 1 Fuel & air metering
- 20 Specific fault
Symptoms
- Check engine light, often with a reduced-power or limp mode message
- Throttle response that suddenly goes soft, then returns after the car is restarted
- Code set only while driving over bumps or when shifting position in the seat
- Idle speed normal but acceleration capped well below normal
- Pedal D reading that flickers or briefly drops to 0 V while the pedal is held still
Possible causes
Ranked by how often each cause is behind this code (editorial estimate).
- Poor terminal fit or corrosion in the pedal module connector
- Intermittent fault inside pedal sensor D
- Harness chafed between the pedal and the PCM, often at dash brackets or the firewall pass-through
- Water in the driver footwell reaching the pedal connector
- Wiring spliced or damaged during installation of a remote starter or other accessory
- PCM connector or internal input fault
Diagnosis step by step
Check whether the fault is present now
Look at the code status and the freeze frame, then watch pedal D with the key on and your foot off the pedal. A healthy reading holds within a few hundredths of a volt. A steady, normal-looking value means the fault is intermittent and you'll need to provoke it.
Tools: OBD-II scanner
Provoke it with a wiggle test
With pedal D displayed or graphed, flex the harness in sections: at the pedal connector, along the dash brackets and where it passes through the firewall toward the PCM. Also tap the pedal module body. The section that makes the reading jump contains the fault.
Tools: OBD-II scanner, Flashlight
Check terminal tension at the pedal connector
Disconnect the pedal and inspect the D reference, ground and signal terminals. Slide a matching male test terminal into each female terminal; it should drag noticeably. A terminal that feels loose, is green or has been pushed back will cause exactly this kind of intermittent loss.
Tools: Flashlight, Pliers
Measure the D circuit wire by wire
With the key on and the pedal unplugged, the D reference should read 4.9–5.1 V and the D ground should show continuity to chassis ground. With the battery disconnected and the PCM connector unplugged, each D wire should measure under about 1 ohm end to end and show no continuity to other wires.
Tools: Multimeter
Look for accessory wiring
Follow the harness under the dash for tapped or spliced wires from remote starters, alarms or dash cams. Poorly made splices or scotch-lock connectors on the pedal wiring are a known source of intermittent pedal codes.
Tools: Flashlight
Replace the pedal if the wiring is clean
If the circuits test good and the fault follows the pedal, replace the pedal module; the sensors aren't sold separately. Clear the codes, key off for about ten seconds and confirm D reads correctly at rest and at the floor.
Tools: Screwdriver, OBD-II scanner
Where the parts are
- 1Ignition coil
- 2Spark plug
- 3Fuel injector
- 4Camshaft sensor
- 5Crankshaft sensor
- 6Engine computer (ECM)
- 7Intake manifold
Repair options & costs
| Repair | DIY? | Estimated cost |
|---|---|---|
| Repin or replace the pedal connector | No | $80–$220 |
| Repair chafed pedal harness or bad accessory splices | No | $120–$380 |
| Replace accelerator pedal module | Yes | $150–$450 |
| Fix footwell water leak and dry the connector | No | $100–$500 |
Rough US estimates for parts and labor; shop rates vary by region. Not a quote.
Emissions / smog test impact
Will fail
P2120 keeps the check engine light on, so the vehicle fails an OBD-II emissions inspection. An intermittent fault may also return shortly before the test, so fix the cause rather than just clearing the code.
Frequently asked questions
What's the difference between P2120 and P2122 or P2123?
P2122 and P2123 say the D signal is stuck too low or too high. P2120 is the broader circuit code, used by many PCMs when the signal drops out briefly or behaves erratically, which usually points to a connection rather than a completely failed sensor.
Why can I still drive with P2120?
The pedal has a second sensor, E. With D untrustworthy, the PCM follows E but restricts how far and how fast the throttle opens, so you can reach a safe place without full power.
The code started after a remote starter was installed. Related?
Quite possibly. Some installations tap into wiring behind the dash, and a loose splice or damaged insulation on the pedal circuit causes exactly this kind of intermittent fault. Have the installation checked before replacing the pedal.
Which of the pedal sensors is D?
D is the primary accelerator pedal sensor, sometimes labeled APP1 or VPA in service information. E is the secondary sensor, and on some vehicles there's a third sensor F.