The Quick Answer above is the generic definition. What follows is what is documented for the Honda models that log P0121, checked against manufacturer data and owner reports.
DTC/P0121·Honda
P0121 on Honda: Causes, Symptoms and Fix Cost
Quick Answer
Moderate SeveritySafe to drive (short-term)Honda
P0121 on a Honda means the throttle position sensor A signal is in range electrically but doesn't match what the ECU expects from RPM, MAF, and pedal inputs. Result: the ECU stops trusting the throttle and usually forces limp mode.
Repair cost on Honda€48 - €730
Connect any standard Bluetooth OBD2 adapter to your Honda and Skanyx tells you what P0121 means on that engine, whether it is safe to keep driving, and what the fix should cost. Free on iPhone and Android.
Get Skanyx freeWhat does P0121 mean on a Honda?
Honda Civic
2006-2015 (R18A1 1.8L, K24Z 2.4L Si)Less common on Hondas than European cars. When it does appear it's usually the accelerator pedal position sensor or chafed wiring at the throttle connector rather than the throttle body itself. Honda's TPS relearn is simple: key on 2 seconds, off 10, repeat 3 times, then idle for 10 minutes.
What causes P0121 on a Honda?
Beyond the generic causes listed on the main P0121 page, these are the documented Honda-specific patterns:
Honda CivicFailed accelerator pedal position sensor (pedal assembly replacement)
Honda CivicChafed harness where it crosses the intake manifold
How to diagnose P0121 on a Honda with OBD2
Follow these steps to pinpoint the root cause of P0121:
- Scan for all stored and pending codes. P0121 rarely shows alone; sister codes like P0122, P0123, or P2135 point straight at the fault
- With key on engine off, log TPS1/TPS2 (or APP1/APP2) voltages. Expect roughly 0.5-0.9V closed and 4.0-4.5V wide open, with the two signals tracking correctly
- Slowly sweep the throttle from closed to WOT while logging. Any dropout, spike, or flat spot in the trace is a worn sensor track
- Inspect the TPS connector for bent pins, green corrosion, or oil contamination pooling from a leaking valve cover gasket
- Back-probe the 5V reference and ground at the sensor. Expect close to 5.0V reference and under 0.1V on ground with key on
- Remove the intake boot and check the throttle plate. Clean with throttle body cleaner if coked, but don't force a drive-by-wire plate open by hand
- If the sensor is integrated in the throttle body and readings are still erratic, replace the throttle body assembly
- After any repair or cleaning, run the manufacturer's throttle body / idle relearn procedure with a capable scan tool
How much does P0121 cost to fix on a Honda? (EUR)
Estimated repair costs for P0121 in EUR, compiled across makes. Honda costs typically sit in the middle of each range.
Prices estimated as of March 2026. Costs vary by region, vehicle, and shop.
Related codes that often appear with P0121 on Honda
These codes commonly cluster with P0121 on Honda vehicles:
Looking for the full P0121 reference (all makes, full diagnosis flow, complete repair cost matrix)?
See the main P0121 guideSkanyx · Honda
Diagnose P0121 on your Honda
Your car logged P0121. Skanyx reads it on any standard Bluetooth OBD2 adapter, tells you whether it is safe to keep driving, and shows the €48-€730 repair range so you know the number before a shop quotes you. Free on iPhone and Android, and you do not need to be a mechanic to read it.
Get Skanyx free