P0121 on Cadillac: How to Diagnose & Fix
Throttle/Pedal Position Sensor Circuit Range/Performance
1 Cadillac model · 1 documented issue · $150-$1,800 repair
P0121 on Cadillac by model: symptoms, diagnosis and fix
GMT900 Escalades commonly throw 'Service StabiliTrak' and 'Service Traction Control' together with a reduced-engine-power event, and owners chase it for months because three unrelated root causes present identically. The most common is the electronic throttle body - carbon buildup on the blade and a worn throttle position sensor track make the two APP/TPS signals disagree, the PCM defaults to limp mode, and StabiliTrak disables itself because it can no longer command torque reduction. The second is the brake pressure sensor or the EBCM internally, which sets a chassis code and disables ESC without any engine symptom. The third is a weak battery or corroded ground causing a low-voltage brownout that trips every chassis module at once. CarComplaints lists 'Stabiltrak Light On' as the #3 problem on the 2007 Escalade at an average of $1,800 and 75,000 miles, and the 2007 model year carries 41 NHTSA engine complaints alongside a large ESC-related brakes group on 2011.
Common Symptoms
- Service StabiliTrak and Service Traction Control messages appear together
- Engine Power Reduced message with the vehicle limited to low speed
- Warning lights clear after an ignition cycle then return under load
- ABS and traction control lights on with normal braking otherwise
- Rough or surging idle after the throttle fault
How to Fix
Scan for chassis codes, not just powertrain codes - a generic OBD2 reader that only sees P-codes will miss the C-codes that actually identify the fault. C0561 alone means the module disabled itself because something else failed and is not the root cause; look for the code that set alongside it. If the event includes reduced engine power with a throttle-correlation code, remove and clean the throttle body with throttle-body cleaner and a soft cloth (never scrape the bore coating), then perform the idle relearn; if the fault returns, replace the throttle body, roughly $250-$450 installed. Before any of that, load-test the battery and clean the battery terminals and the engine-to-frame grounds - low voltage is the single most common cause of a multi-module StabiliTrak complaint and costs nothing to rule out. If the codes point at brake pressure sensing, the sensor is serviceable on many of these and is far cheaper than the EBCM; only condemn the EBCM after the sensor and its wiring check out. EBCM replacement or rebuild runs about $500-$1,200.
Sources for this issue (2)
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 Cadillac?
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 Cadillac it is documented across 1 model: Escalade.
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 Cadillac?
Published repair estimates on Cadillac range from $150 to $1,800 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.