P0121: Throttle/Pedal Position Sensor/Switch A Circuit Range/Performance
A generic powertrain (engine and transmission) trouble code, same meaning on every brand.
Expect reduced-power (limp) mode. Driveable to a shop at low speed; do not plan highway trips.
Symptoms
- Reduced power / limp mode
- Erratic or high idle
- Poor throttle response
Likely causes, most common first
- Throttle position sensor wear or contamination
- Carbon-fouled electronic throttle body
- Wiring or connector faults in the TPS circuit
Read P0121 yourself before paying for diagnosis
A basic Bluetooth OBD-II scanner ($20-40) plugs into the port under the dashboard and shows this code with live sensor data on your phone - useful both for confirming the fix and for talking to a shop from an informed position.
What is going on and how it gets diagnosed
P0121 means the throttle position signal disagrees with what the airflow and pedal data say should be happening. Because drive-by-wire throttles are safety-critical, the computer responds conservatively - often cutting power rather than trusting a suspect sensor.
Many modern throttle bodies integrate the sensor, making cleaning plus a relearn procedure the first step and unit replacement the second. After any throttle work, the relearn matters: skipping it leaves idle hunting and can re-set the code on a healthy part.
Repair options and cost
Typical US independent-shop ranges, parts and labor. Dealers run higher; regional labor rates vary.
Owner reports mentioning P0121
“While randomly driving my check engine light and throttle light comes on. I've had my car to the dealer multiple times. The codes are p2135 and p0121. Dealer said they can't find anything wrong. They didn't clear the code. Went home and slept, next morning the lights are off. This has been a continuous issue. They replaced the throttle body december 2018, my gas pedal 2 months ago and part of my computer over a month ago and this is still happening. I've read in a bunch of forums this is common but no one has a solution. Dealer said my wiring harness was fine and they can't find the problem but don't want to replace the throttle position sensor even though it's under warranty. Help”2015 Jeep Patriot · Aug 2019 · 86,000 mi
“The brakes will activate by themselves with no foot on brake. With no notice it will turn into a full panic stop. Simply driving and all of a sudden the brakes go to full lock. A very very dangerous situation. Once the speed gets below a certain mile per hour it changes. If one stops and turns the engine off and restarts its fine. This started early this year and now has become more frequent. The last 2 times car was driven this has happened. When it is scanned its coming up with 2 u codes p0100-20 and p0121-20”2009 Ford Taurus · Aug 2017 · 113,000 mi
“Diagnostic code p0121 - throttle body it is a common issue among all denali owners and is covered under warranty. But if this issue is known by the manufacturer this should be a recall as this could cause an accident. Solution is to replace the throttle body (which are currently on back order) dealers will charge between $95 & $110 to diagnose the problem and determine if it is covered under warranty. Owners should be weary of dealers trying to charge for this fix. Especially of the denali is under 100k miles. *tr”2007 GMC Yukon Denali · Aug 2012
Show 4 more owner reports
“Vehicle cut out on ca freeway 57 at 70 mph due to throttle position sensor fault, (fault code p0121) luckily I managed to get to the hard shoulder without incident. This condition is extremely dangerous especially if this had happened while I was turning in front of oncoming traffic. I was a toyota/mercedes tech for 30 years. *tr”2004 Jaguar XJ8 · Nov 2010 · 74,302 mi
“I have a 2006 toyota corolla, with intermittent problem with the acceleration of the car. I took it in and the dealer is saying that there is not problem with the acceleration of the care. But they said there is a bad throttle position sensor and that it would cost we $1200.00 to repair. (the acceleration problem has occurred 3 of 4 times in the past 6 months. They are say is code # p0121. Throttle position sensor out of range. *tr”2006 Toyota Corolla · Dec 2009 · 52,000 mi
“2005 ford f150 vehicle loses power and all control while driving on the road. This happened at least six times. Very lucky traffic was light most times but one almost a caused rear end collision. I replaced a throttle sensor and the problem disappeared and the problem returned after a couple of weeks. I took it to the dealer and they replaced electronic throttle body and throttle body and motor assembly. They also performed pcm reflash power train control module and retest. The codes received with scan tool were p0121, p2104 and p2112. *tr”2005 Ford F-150 · Aug 2009 · 73,500 mi
“While driving 35 mph my ford f150 truck engine shut down. The truck lost all power brakes and steering. Seconds before it stalled a engine malfunction light came on. I was only able to re-start after coming to a complete stop, placing the truck in park and turning the key off then back on. Took it to dealer and they road tested and diagnosed codes; p2104, p0121 and p2112. Pinpointed and found electronic throttle body physically sticking closed. Replaced etb and retested ok after repairs. This was not covered under warranty. Time of failure the truck mileage was 33900. See service repair order. *tr”2005 Ford F-150 · Jan 2009 · 33,900 mi
Cars that report P0121 most often
Based on mentions of this code in NHTSA owner complaints.
Frequently asked questions
Can I drive with P0121?
Expect reduced-power (limp) mode. Driveable to a shop at low speed; do not plan highway trips.
How much does it cost to fix P0121?
Typical US repair costs range from $100 for the simplest fix (throttle body cleaning + relearn) to $800 in the worst case. The right number depends on which cause your car has - see the causes list.
Definition per SAE J2012 standard nomenclature. Symptoms, causes and costs are editorial guidance - always confirm with a diagnosis of your specific vehicle.