[Tutorial] Hyosung GV650 & GT650: Tip Over Sensor (TOS) Bypass Mod & C23 Fix
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Fixing the C23 Error: GT650 & GV650 TOS Modification
If your Hyosung GT650 or GV650 is showing a persistent “FI” error on the dash and refusing to prime the fuel pump, you may be dealing with a faulty Tip Over Sensor (TOS). When this sensor fails, the ECU assumes the bike has crashed and cuts the ignition for safety. This guide explains how to bypass the sensor using simple resistors to get your V-Twin back on the road.
🔧 Diagnostic & Modification Info
The TOS is designed to kill the engine if the bike tilts past a specific angle. Over time, the internal float can stick or the circuit can fail, triggering the Dealer Mode Error Code C23. A new sensor can cost upwards of £80–£100, but a bypass can be made for pence.
- Fault Code: C23 (Tip Over Sensor Malfunction).
- The Symptoms: “FI” on dash, fuel pump won’t prime, engine dies after 2 seconds.
- The Fix: Replacing the internal sensor circuit with two specific resistors to “trick” the ECU into seeing a safe upright position.
- ⚠️ Warning: This mod disables the automatic engine kill-switch during a crash. Perform at your own risk.
Credits: We owe a massive thanks to the original author for documenting this electronics bypass. This PDF is a permanent mirror hosted by HyoRiders. If you’ve successfully cleared your C23 error using this method, please leave a comment to help others!
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Very interesting modification, and no other like it on the net. I have problem with my gv650 efi that could be related to the above, Bike was working perfectly, decided to do a basic service on it, Plugs, oil & filter etc, lifted the tank from where 2 bolts by the battery and used the stay to keep it up, for access to the rear plug, all good so far, had to unbolt the rad and fan etc to allow access to the front plug (stupid design) any how once done turned ignition on (while tank still lifted) to find the pump would go through its prime cycle, (as if the kill switch was on, but wasn’t) it then shortly came up with “CHE” on the dash (the only fly in the ointment to your comments should be F1 – nope) my lad came to help and I said it wont work, he sat on on the bike and turned the ignition on and yep, it primed and started perfectly! Grrr. This took my attention to the side stand switch, duly changed and nope, same issue seems temperamental when works not work and nothing moved or change to reflect this again Grrr. Have just received a new starter solenoid/relay but my gut says this isn’t the cause as it seems a safety issue cutting power to the pump a’la your topic. Where is the TOS sensor fitted on these? can it be tested easily? and if i was to replace it you say can use one from another manufacturer, I’m guessing connection is the same, do you know the cheapest option short of your mod? Any suggestion or thought would be appreciated as bike hasn’t been used since April and we have had the best summer since 1976!!
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Hey,
According to the manual – The RO Switch (Roll Over) aka. (TOS Tip Over Sensor) is under the seat.
It should be near the battery, if you read the above ^ pdf file, you would have a visual idea of where it is.According to the service manual (EFI), this is what it says:
“CHE” : The LCD panel ① indicates “CHE” letters when no communication signal from the ECU is received for 3 seconds.
C23 = RO/TOS Switch faulty.
For a more detailed explanation. Download the link below and go to pages:
#27, #34, #47, #66 ,
– Service Manual Link –Personally I don’t have a TPS sensor on mine, if it did, i’d find ways to get rid of it myself. But i have no experience in using other brand manufacture TOS sensors on a GV650
However, the above ^ book at the top, does mention that you may use other brands from “EFi/Ei” (injected bikes.) Designs may also vary too.
This is the most recent TOS sensor hyosung uses that I know dealers to be stocking up,
Hope this info helps, let us know how you get on!
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I did not write this , but give credits to the lad who made this. (BTW, follow at your own risk!)
Quote from book :
The TOS sensor, the same in the GT650 and GV650, turns the ignition off when an emergency happens such as excessive tilting or the tipping over of the bike. If the sensor is not working it will create a situation whereby after a short time of about 2 seconds after the ignition is switched off the injection pump is disabled and you cannot fire up the engine. When this happens, the display will always show an “FI” error. When this happens the sensor should be checked. Put the bike into service mode. There should be displayed error c23. This means that the sensor is faulty and needs replacing. If there is any problem with buying a new sensor, or the price of about $ 100 is too high, you can hand-edit the faulty sensor for the engine to run properly not display FI error. The cost of modification is only the purchase of two resistors in the price of .30₵ – .40₵ cents. The only drawback of this modification is that if you tip over the bike while running, the ignition will not be stopped.
DOWNLOAD / VIEW – 650cc Twins – Tip Over Sensor Mod (.pdf) -
a great mod, and may give it a go, i have actually replaced the TOS sensor with a Triumph one, along with several other bits, my feeling is issue related to the clutch switch, as playing with the connector did have an effect! I currently have it loose on the bar but now not working at all, will look at doing a by pass on this switch (easy) and see if that fixes it, shame as scared to use bike as may end up a way from home and not be able to start the bike, the bikes mint and only done 5k since new, i serviced it a year ago and refitted a rack that came with it and put new saddle bags and tool roll for it to be sat under a cover, hey ho is the anniversery model no. 69 so dont thin i will lose money if i decide to move it on. Thanks guys for help.
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I did not write this , but give credits to the lad who made this. (BTW, follow at your own risk!)
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Quote from book :
The TOS sensor, the same in the GT650 and GV650, turns the ignition off when an emergency happens such as excessive tilting or the tipping over of the bike. If the sensor is not working it will create a situation whereby after a short time of about 2 seconds after the ignition is switched off the injection pump is disabled and you cannot fire up the engine. When this happens, the display will always show an “FI” error. When this happens the sensor should be checked. Put the bike into service mode. There should be displayed error c23. This means that the sensor is faulty and needs replacing. If there is any problem with buying a new sensor, or the price of about $ 100 is too high, you can hand-edit the faulty sensor for the engine to run properly not display FI error. The cost of modification is only the purchase of two resistors in the price of .30₵ – .40₵ cents. The only drawback of this modification is that if you tip over the bike while running, the ignition will not be stopped.<hr />
<h3>📕 DOWNLOAD / VIEW – 650cc Twins – Tip Over Sensor Mod (.pdf)</h3>
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