P0121 on Pontiac: How to Diagnose & Fix
Throttle/Pedal Position Sensor Circuit Range/Performance
1 Pontiac model · 1 documented issue · 1 critical · $250-$500 repair
P0121 on Pontiac by model: symptoms, diagnosis and fix
G6 owners frequently see a 'Reduced Engine Power' message with the car dropping into limp mode, triggered by throttle position sensor voltage-correlation faults. The throttle body's integrated TPS develops dirty or shorting solder points (sometimes attributed to 'tin whiskers') and corrosion at the connector, so the two throttle sensor signals disagree and the ECM cuts power for safety.
Common Symptoms
- Reduced Engine Power warning message
- Sudden loss of acceleration / limp mode
- Hesitation or rough idle
- Check engine light
How to Fix
Inspect and clean the throttle body and TPS connector; check wiring for corrosion/water intrusion. The common fix is replacing the electronic throttle body assembly; relearn the throttle after replacement.
What you need to fix it
Only diagnosis- and fitment-reviewed repair parts are linked here.
- GM 19300180 throttle-position sensor kit
Confirm the installed throttle body is the applicable Hitachi design and verify by VIN before purchase.
- GM 12609500 electronic throttle body assembly
2006-2010 Pontiac G6 3.5L or 3.9L as cataloged; confirm VIN, throttle manufacturer and supersession before ordering.
- GM 12615503 electronic throttle body assembly
2007-2009 Pontiac G6 3.6L as cataloged. Does not cover the 2.4L, 3.5L or 3.9L branches.
- GM 12631186 electronic throttle body assembly
2008-2010 Pontiac G6 2.4L; GM catalog supersession may be 12694871. Excludes 2006-2007 2.4L until a VIN-matched catalog path is verified.
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Sources for this issue (3)
P0121 code reference
General diagnostic-code context. The code alone does not confirm a cause for your vehicle; use the applicable issue card and its sources.
Frequently asked questions
What does P0121 mean on a Pontiac?
P0121 stands for "Throttle/Pedal Position Sensor Circuit Range/Performance." This code means the throttle position (or accelerator pedal position) sensor's signal does not match what the computer expects compared with other inputs like airflow, RPM, and the second throttle/pedal sensor. The sensor tells the computer how far the throttle or pedal is open; when its range or performance is off, the computer can't trust how much power you're requesting. You may notice hesitation, surging, poor acceleration, rough idle, or the vehicle dropping into a reduced-power 'limp' mode. It indicates an out-of-range or implausible signal rather than a complete loss of signal. On Pontiac it is documented across 1 model: G6.
What are the most common causes of P0121?
The most common causes of P0121 are: Worn or failing throttle position sensor, Dirty or carboned-up throttle body affecting plate position, Damaged, frayed, or shorted sensor wiring, Corroded or loose sensor connector, Poor sensor ground or reference voltage, Faulty throttle body / electronic throttle actuator, Mismatch between the two throttle or pedal sensor signals. The specific cause varies by vehicle.
How much does it cost to fix P0121 on a Pontiac?
Published repair estimates on Pontiac range from $250 to $500 depending on the model and root cause. If an issue mentions a recall or campaign, check your VIN with the manufacturer or NHTSA and confirm eligibility and coverage with a dealer.
Looking for P0121 on a different make?
View P0121 across all makes →Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.