Throttle/Pedal Position Sensor/Switch D Circuit High
The P2123 code means the vehicle's onboard diagnostic system has detected: Throttle/Pedal Position Sensor/Switch D Circuit High. This is a critical severity code.
- Keep driving?
- No -- stop driving
- DIY difficulty
- moderate
- Estimated cost
- $100 - $400 (parts and labor)
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Common Symptoms
- Engine surging or high idle
- Unintended acceleration concern
- Reduced power mode activated
- Throttle warning light on
- Check engine light on
Probable Causes (Ranked by Likelihood)
- APP sensor D signal wire open or shorted to voltage Very High
- Disconnected APP sensor connector High
- Faulty APP sensor (stuck high output) Moderate
- Corroded wiring causing open circuit Moderate
- APP sensor reference voltage shorted to signal wire Low
Step-by-Step Diagnostic Procedure
-
Check APP sensor D voltage -- should be 0.5-0.8V at rest, not near 5V
-
Verify APP sensor connector is fully seated and not disconnected
-
Disconnect sensor and check if signal wire voltage drops -- if not, wire may be shorted to 5V reference
-
Inspect wiring harness for damage where reference and signal wires run together
-
Replace APP sensor assembly if connector and wiring test good
Frequently Asked Questions
Can I drive with code P2123?
No. A high signal on the APP sensor D circuit could be interpreted as a full throttle request. The PCM enters reduced power mode to prevent unintended acceleration. Have the vehicle towed for repair.
Could a disconnected plug cause this code?
Yes. When the APP sensor connector is disconnected, the PCM reads the 5V reference voltage on the open signal wire, interpreting it as a high (full throttle) input. This is one of the first things to check.
Is the accelerator pedal position sensor serviceable?
On most modern vehicles, the APP sensor is integrated into the pedal assembly and replaced as a unit. The pedal assembly typically costs $80-$250 and takes 30-60 minutes to replace. No special tools are usually required.
Sources
This page is built from documented references. Verify against your own service info before repair work.
P2123 on Diesel, EV & Equipment
The same code ID appears across other engines and platforms. The diagnostic flow varies by manufacturer — these are the platform-specific breakdowns:
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