Suzuki FI Code C21: Intake Air Temp Sensor — Causes & Fix
On Suzuki motorcycles and scooters, FI code C21 means a fault in the intake air temperature (IAT) sensor circuit — used to fine-tune fuelling for air density.
- Applies to
- Suzuki motorcycles
- Est. repair cost
- $15 – $85
- Time to fix
- 30–90 minutes
What it means
Typical causes are a loose/corroded connector, damaged wiring, or a failed IAT sensor. This is a generic Suzuki fuel-injection (FI) code, so it applies across Suzuki FI models — the Raider R150 Fi, Smash, Gixxer, GSX-R and GSX-S range, V-Strom, and more. Suzuki reports it as a "C" number, shown through the FI-light blink pattern or by entering the bike’s dealer/diagnostic mode. After the fault is repaired it becomes a stored "history" code; clear it through Suzuki’s dealer/diagnostic mode so the FI light goes out.
Symptoms
- FI light on with code C21
- Slightly rich or lean running (usually mild)
- Small change in economy or throttle feel
How to fix it
- 1
Inspect and test the sensor
1. Find the IAT sensor (airbox/intake). 2. Reseat the connector; measure resistance against the temperature chart. 3. Replace if out of spec, then clear the code.
Frequently asked questions
Is code C21 serious?
It’s usually one of the milder faults — the bike often runs nearly normally. Still worth correcting so fuelling stays accurate.
Last updated July 15, 2026
Guidance only — always consult a qualified professional or the official service manual before carrying out repairs.