Throttle Body 16400-HP5-604 for Honda ATV Rancher TRX420 2007-2008

Throttle Body 16400-HP5-604 for Honda ATV Rancher TRX420 2007-2008

This throttle body assembly is engineered as a direct replacement for the Honda ATV Rancher TRX420 2007-2008. Manufactured to meet or exceed OEM specifications, it delivers reliable performance in demanding conditions. Each unit is tested for fuel flow, pressure rating, and durability before leaving the factory to ensure consistent quality across every order.

Vehicle Compatibility

Replaces OEM Part Numbers

16400-HP5-604 • 16400HP5604 • 2007-2008

Signs You Need a Replacement

If your equipment is showing any of these symptoms, the throttle body may be the cause:

• Surging or fluctuating idle speed — The throttle plate or motor is sticking, causing the ECU to hunt for the correct idle position. This is the most common early symptom.
• Reduced throttle response — A dirty or worn throttle body doesn’t open smoothly. You’ll notice a dead spot or hesitation when you press the pedal.
• Check engine light with P0121 or P1545 — These codes indicate a throttle position correlation error. If cleaning doesn’t clear them, the throttle body needs replacement.
• Limp mode activation — The ECU limits engine speed when it can’t trust the throttle position signal. This safety mode prevents damage but limits operation.
• High idle that won’t come down — Carbon buildup holds the throttle plate slightly open. The ECU compensates by raising fuel trim, which may trigger adaptive mixture codes.
• Stalling at low RPM — When the throttle body can’t maintain a stable idle, the engine may stall at stoplights or when shifting from drive to reverse.

Post-Installation Adaptation

After installing the new throttle body, perform a throttle adaptation so the ECU learns the new zero and full-throttle positions. With VCDS or equivalent: go to Engine, Basic Settings, channel 060 or 098 (varies by ECU), and follow the on-screen prompts. Without a diagnostic tool, use the manual method: turn the key ON (engine off) for 60 seconds, then OFF for 10 seconds. Start the engine and let it idle for 3 minutes without touching the accelerator. Do not rev the engine during this process.

Frequently Asked Questions

Will this fit my Honda TRX420?
Yes. This part is designed to fit the Honda TRX420 among other models listed in the compatibility table above. Verify your specific model and engine code before ordering to ensure the correct fit.

Can I cross-reference 16400-HP5-604 with 16400HP5604?
Yes. Both 16400-HP5-604 and 16400HP5604 are interchangeable OEM numbers for this part. They refer to the same component with the same specifications, just different part number revisions.

How do I check if my engine code (TRX420) matches?
The engine code is stamped on a metal tag attached to the engine block, usually near the timing belt cover or on the cylinder head. Compare the code you find with the list above. Engine codes are 3 to 6 characters long.

My vehicle is a 2007 model – is it covered?
The compatibility range for this part includes 2007-2008. The 2007 model year falls within this range, but verify the engine code and body type match. Mid-year production changes sometimes mean two vehicles from the same model year use different parts.

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