Hitchcocks Forum

Hi, just started what was meant to be 3 days pootling around the Cotswolds on Euro IV C5. After ~100 miles driving down, the bike began running rough. Felt like a problem with the fuelling, running fine, then stuttering, then running fine again. Have refilled the bike at local petrol station and now the MIL light is on constantly. The workshop manual says if the MIL light stays on: "Sensor Coupler Loose Connection - Check for any EFI sensor coupler loose connection and correct them" or "Any EFI Sensor Failure - Check & replace the same". Does anyone know which 'sensor couplers' I should be checking and where they are??? Anyone got any helpful suggestions, or is this a 'take it back to the dealer' sort of problem? Thanks, Tom.

Hi Tom, its unusual for it to be as simple as a disconnected connection but its always worth a quick check before going back to the dealer. In my experience, the easiest connection to become unsecured is the TPS sensor, this is located on the throttle body on the horizontal plane (battery side). The battery is very close to this sensor, and occasionally when the battery's get fitted the sensor can be unsecured from its connector and then begin to work loose when in use. If this is the case it will be obvious, but you will just need to pull the battery forward slightly to gain access and check the connection. 


 The other places to check for a Euro 4 (2017+) model would be:

- Oxygen sensor (just on the front of the exhaust pipe and follow the wire up to the block connector)

- Crank position sensor (follow the wires from the top of the right hand cover, the block connector to check is usually between the battery and left hand tool box, there will be a big red block connector for the alternator and a smaller 2 pin connector for the crank position sensor, this 2 pin connector is the one to check. Unlikely to be this sensor as the bike will not run if disconnected)

- Air temperature sensor (back side of the airbox)

- Coil connections (from coil located above the cylinder head. Again, unlikely to be this sensor as the bike will not run if disconnected)

- All sensors on the throttle body (TPS, MAP and Injector)

- Air injection system can also flag a fault code (located above the cylinder head) 


If you do find loose connection and plug it back together, the engine check light may take a few cold starts for the light to turn off even when the engine is performing as it should. If you wanted to go a step further, you can make the bike perform a "self diagnosis" which would help to narrow down which sensor it thinks is causing the problem.



Hope this helps!

I don't know about Euro IV models that are supposed to have a better EFI system than the earlier ones, but, yes, been there and had to deal with that on my 2015. If it's similar you need to find the small wire from the ECU that isn't connected to anything. Earth it and switch on the ignition but don't start the engine. The MIL will produce a series of short and long flashes. These are listed in the w/s manual and tell you which sensor input is kaput. Usually the problem is nothing more than a loose or dirty connector to a sensor. In my case it was the throttle position sensor. The fix is usually simple; finding the issue can be tricky. I used to carry a picture of all the fault codes on my iPhone. In the end I put a carb on it and sorted it for good....Another common issue was the little earth wire to the -ve battery terminal. On the C5 especially ( because the battery cables were too short) the wire could break, causing intermittent contact and the running issues you describe. This was a quite common issue. The other one is the infamous side stand switch playing up. Many, like me, have disconnected this troublesome item and now rely on proper pre-ride checks again - a bit radical.......TBH if you are unclear about the purpose and location of the various sensors take it back to the dealer to sort under warranty. It is easy to identify with DOL, the dealer diagnostic kit. Good luck.

Dan, RB, thanks both. I'll go and have a quick look at these areas and see if I can find a loose connection. Otherwise, back to the dealer she goes.

Had this same problem out on the road with my CGT one day. and the fix on the side of the road was to wiggle the main wiring loom under the rear of the petrol tank and hey presto all good again, Took the tank of later to find a bare wire that was shorting out to the fuel pump, A turn of PVC tape and tank back on without trapping wiring loom and all is well, The couplings in the wiring loom to check are the relays in l/hand tool box, pull out push back in, these must be a tight fit and the two connections on the throttle body under rear of petrol tank also connecter in the wire that goes to the fuel pump also under rear of petrol tank, I have these days treated my self to a can of electrical contact cleaner and use this any time a pull connections apart.

Oddly, all seems to be well this morning. Fuelling fine and no MIL light. If the problem doesn't come back, I'll get on with my holiday as planned and take the bike to the dealer when I get back. Thanks for the help guys.

Hopefully should be fine. The majority of reported EFI problems on various forums appear to have been down to shoddy factory line assembly work in the form of loose wiring loom connector blocks.
Fortunately the actual components themselves seem to be robust enough. There have been a couple of pump failures but even one of the Japanese big four suffered this because the dealers failed to adequately flush the tank preservative out during the predelivery checks clogging the filter.

Cheers Ric, that's reassuring. I'll check all the connectors ASAP.

Hi, the MIL light came on again the next day and the bike ran rough again. Checked and secured all the connectors around the battery (not sure which was which) and all sorted. Has run perfectly down from Cotwolds to Cornwall. Thanks for the help everyone. Tom.

Embarrassed to admit this but... same thing happened again recently, as soon as I'd got the bike back from Haywards. when I phoned up they asked if I'd done anything since I got the bike back. Filled it up was the answer. Apparently the new Euro IV are *horribly* fiddly on filling - there's an new widget in the fuel filler that is very very easy to splash fuel into, which runs down into a catch-pot somewhere near the crank-case, then back into the fuel injector. If you spill fuel into this system, then the bike starts to run rough about ten miles later. I'm pretty sure this is what happened when I was in the Cotswolds and same again now. I feel like a bit of a plonker with this, but I've never had a bike so fiddly to fill without splashing as the new Euro IV, nor one so badly affected if you do manage to splash a bit.