Suzuki Fault Code

Free · no signup

Code 21 / P0120

Hesitation Off-Idle / Bucking on Accel

System

Throttle / Controls

Symptom

Hesitation Off-Idle / Bucking on Accel

Diagnosis & fix steps

LOGIC: Throttle Position Sensor (TPS) Circuit Voltage Out of Range. ACTION: Check 3-pin or 4-pin TPS connector on throttle body. Backprobe signal wire (yellow/blue) to ground; verify smooth sweep without voltage dropouts (spec: ~0.5V closed to ~4.2V wide open).

Red Seal field insights

Rotary Wiper Wear: Kei truck stop-and-go delivery duty wears down the internal carbon film track right at the off-idle transition zone (0.8–1.2V), causing severe acceleration stumble.

Same code keeps coming back?

That's a program problem, not a part problem. Book a 30-minute uptime review with Grant, a Red Seal Heavy Duty Technician.

Book an uptime review

Read before you touch anything

  • This is general reference information, not a repair manual. It is for trained, qualified technicians.
  • Fault codes, meanings and procedures vary by model, serial number and software version. Confirm the code and the procedure against the manufacturer's service manual before acting.
  • Follow the OEM service manual, torque specs and your site's safety procedures: lockout/tagout, block raised equipment, relieve hydraulic, fuel and air pressure, and let hot systems cool.
  • You use this information at your own risk. Adventure Mechanical and AM Fleet Integrity accept no liability for damage, injury, downtime or loss arising from its use.
  • Not affiliated with or endorsed by any manufacturer. Brand names are used only to identify the equipment a code applies to.

Track this across your whole fleet

This code is free to read. AM Fleet Integrity lets your team log fault codes against assets, plus the full fault-code library, QR operator reporting, PM scheduling and predictive alerts. Start free — no credit card required.

Start your free trial

Related Suzuki fault codes

← All Suzuki fault codes