2007 GSX-R750 Fuel Pump Not Priming? Here’s Your Step-by-Step Troubleshooting Guide

If your 2007 GSX-R750 cranks over but the fuel pump doesn’t prime (no buzzing sound from the tank when you turn the key on), and the dash shows “CHEC” in the temperature window, the most likely culprit is a failed ECU (Engine Control Module) — not the fuel pump itself. This is a common issue on K6/K7 GSX-R models, often triggered by a bad regulator/rectifier that sends voltage spikes into the ECU.

Before you replace the ECU, you need to rule out simpler problems. The steps below will help you diagnose the issue systematically, saving you time and money. We’ll walk through the most common causes, from the easiest to check to the most serious.

1. What Does “CHEC” Mean?

When you turn the key on and the dash shows “CHEC” instead of the normal temperature reading, your instrument cluster has lost communication with the ECU. This is a critical clue. It means the ECU is either not getting power, or it has failed.

Before you panic, check the basics first:

  • Kill switch: Make sure it’s in the Run position.
  • Side stand: The bike must be in neutral or the side stand must be up. The side stand safety switch can prevent the ECU from powering up.
  • Fuses: Check all fuses, especially the main fuse and the fuel pump fuse. A blown fuse can stop the pump and the ECU from working.
  • Battery voltage: A weak battery can cause glitches. Make sure your battery has a good charge (12.6V or more when resting).

If all these check out and the dash still shows “CHEC,” move on to the relay and wiring.

2. Check the Fuel Pump Relay and Wiring

The fuel pump relay is a common failure point. It’s a small black relay under the fuel tank. Here’s how to test it:

  1. Locate the relay: It’s usually near the fuse box, under the tank.
  2. Swap it with another relay: You can swap it with the fan relay (they are identical). If the pump primes after the swap, the relay was bad.
  3. Test with a multimeter: If you have a voltmeter, check the relay socket. The Orange/White wire should have 12V when the key is on. The Red/Blue wire should have 12V all the time. The Yellow/Black wire is the ground trigger from the ECU. If the ECU does not ground this wire, the relay won’t close, and the pump won’t prime.

How to jump the relay: If you want to confirm the pump and wiring are good, you can bypass the relay. Remove the relay and short the Red/Blue and Yellow/Red pins in the socket (use a small piece of wire). The pump should run continuously. If it does, the pump, wiring, and fuse are fine — the problem is the ECU not sending the ground signal.

3. Test the Fuel Pump Directly

If the relay is good, test the pump itself. You can apply 12V directly to the pump connector (the yellow/red wire is positive, and the black/white wire is ground). If the pump runs, it’s fine. If it doesn’t, the pump is bad and needs replacement.

Note: The fuel pump is inside the tank. You can access it by removing the fuel pump plate assembly. The pump itself is replaceable, and the part number for the 2006-2007 GSX-R750 is 15100-01H00.

4. The Tip-Over Sensor (TO Sensor)

The tip-over sensor is a safety device that cuts the fuel pump if the bike falls over. If it’s stuck or faulty, it can prevent the pump from priming.

  • How to test: The sensor is located under the airbox. Unplug it and try to start the bike. If the pump primes, the sensor was the problem. You can also shake it gently — you should hear a rattle inside. If it’s silent, it may be stuck.

5. The Regulator/Rectifier (R/R) and the ECU

A bad regulator/rectifier is a known killer of ECUs on these bikes. When the R/R fails, it can send voltage spikes (over 15V) into the electrical system. These spikes can damage the ECU’s internal circuits, including the one that drives the fuel pump relay.

  • Symptoms of a bad R/R: The battery overcharges, the headlights flicker, or the battery dies quickly. If you’ve experienced any of these, the ECU is likely damaged.
  • What to do: Test the R/R with a multimeter. If it’s bad, replace it before installing a new ECU. Otherwise, the new ECU will also get fried.

6. Error Codes and Dealer Mode

Your 2007 GSX-R750 has a “dealer mode” that can show error codes. To enter it:

  • Use a jumper wire to short the two pins of the diagnostic connector (a white 4-pin connector under the passenger seat or near the battery).
  • Turn the key on. The FI light will flash, and the dash will show a code like C41 (fuel pump relay control system) or C23 (TO sensor).

If you get code C41: This confirms the ECU is not grounding the fuel pump relay. It points directly to a failed ECU.

If you get no code at all: This is also a sign of a dead ECU. The ECU is not responding to the diagnostic request.

7. Is It the ECU or Something Else?

If you’ve tested the relay, pump, fuses, and tip-over sensor, and everything else checks out, but the pump still doesn’t prime and the dash shows “CHEC,” the ECU is almost certainly the cause.

How to be 100% sure: Swap your ECU into a known-good 2006-2007 GSX-R600 or GSX-R750. If the problem follows the ECU, it’s bad.

A note on compatibility: 2006-2007 GSX-R600 and 750 ECUs are interchangeable for testing. The 2005 ECU has different connectors and will not work.

8. A Quick Fix While You Wait

If you need to get the bike running immediately, you can bypass the ECU by wiring a manual switch or a relay to power the fuel pump directly. This is a temporary workaround — the pump will run continuously as long as the ignition is on, which is not ideal for long-term use.

9. Recommended Fuel Pump: KEMSO Racing

If you find that your fuel pump is actually bad, we recommend replacing it with a KEMSO Racing Fuel Pump. KEMSO offers high-performance, OEM replacement fuel pumps that are built to last. They are a direct fit for the 2006-2007 GSX-R750 and come with a lifetime warranty.

KEMSO pumps are designed to handle the pressure and flow your bike needs, and they are a cost-effective alternative to the OEM part. They are also compatible with the GSX-R600 models from the same years.

Visit their website for more details: https://www.kemsoracing.com/

10. Final Checklist

Here’s a quick summary of what to check in order:

  1. Dash display: Does it show “CHEC”? If yes, suspect ECU.
  2. Kill switch and side stand: Both must be in the correct position.
  3. Fuses: Check all fuses, especially the main and fuel pump fuses.
  4. Relay: Try swapping the fuel pump relay with the fan relay.
  5. Fuel pump: Apply 12V directly to the pump to confirm it works.
  6. Tip-over sensor: Unplug it and test.
  7. Diagnostic mode: Check for C41 code.
  8. Regulator/rectifier: Test for overcharging before replacing the ECU.

If you reach step 8 and the ECU is bad, replace it with a used or new unit. Remember to replace the regulator/rectifier first to prevent the new ECU from failing.

For more information on fuel pump replacements, visit KEMSO Racing: https://www.kemsoracing.com/


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