Suzuki GSX-R (2004–2005) STVA ECU

Suzuki GSX-R (2004–2005) STVA Post-Repair Troubleshooting Guide
Important: Use this guide if you reinstalled your repaired STVA (Secondary Throttle Valve Actuator) and the problem is still happening.
Important: Please do not open/disassemble the STVA. Opening it can damage the unit and may void warranty coverage.
Common symptoms this guide helps with:

• FI/diagnostic light on
• Code C28
• “FI” or “F1” showing on the dash
  Step 1: Confirm the correct unit and installation
• Verify the STVA you installed is the original one from your bike (or a confirmed correct match)
• Confirm the STVA is fully seated/mounted and the linkage is correctly engaged (not binding or partially installed)
• Make sure the harness is routed correctly and not pinched after reinstalling the tank/airbox
  Step 2: Battery and charging system check (most common cause of false FI codes)
• With key OFF, battery should be fully charged (weak batteries can trigger FI faults)
• While cranking, voltage should not drop excessively (low cranking voltage can cause actuator/self-test failures)
• With engine running, confirm charging voltage is healthy (charging issues can keep FI faults coming back)
  Step 3: Check fuses and power feeds
• Check the main fuse and EFI/IGN fuses (and any “FI” labeled fuse)
• If a fuse is blown, do not keep replacing it without finding the cause (shorted wiring can mimic a bad STVA)
  Step 4: Connector and pin inspection (do not skip)
• Unplug and re-seat the STVA connector(s) firmly until fully latched
• Inspect for bent pins, pushed-back pins, corrosion, moisture, or loose terminals
• Check nearby connectors that were disturbed during install (ECM area, throttle body sensors, grounds)
  Step 5: Key-ON self-test confirmation
• Turn key ON (engine not running) and listen/observe for the normal throttle/actuator self-check
• If the self-test sounds weak, intermittent, or absent, recheck battery voltage and connector fitment first
  Step 6: Throttle body/secondary plate binding check (vehicle-side mechanical)
• Confirm nothing is physically obstructing the throttle linkage movement (hose routing, wiring, airbox fitment)
• Ensure the secondary throttle plates/linkage move freely and return smoothly (no sticking)
• If binding is present, correct the mechanical issue first (a stuck linkage can trigger C28 even with a good STVA)
  Step 7: Verify related sensors/connectors are connected correctly
• Confirm the throttle position sensor and secondary throttle sensor connectors (if applicable) are plugged in securely
• If any connector was unplugged during service, verify none are swapped/mismatched
  Step 8: Clear codes and re-test
• Clear the FI code using the proper procedure/tool for your bike
• Key cycle, then run the bike and re-check
• If C28 immediately returns, focus on wiring/connectors, battery/charging, or linkage binding
  Step 9: If the issue started right after recent work
• Re-check anything recently touched: tank lift/removal, airbox removal, harness routing, aftermarket add-ons, battery work
• A pinched harness or loose ground after reassembly is a common root cause
  What to send us if the issue continues
• VIN
• Exact dash message and code(s) shown (C28 / F1 / FI light behavior)
• Battery readings (key off, cranking, running)
• Clear photos of the STVA connector pins and the mating harness plug
• Note whether the FI code returns immediately at key-ON or only after starting/riding