G650Xmoto 821 fault code

[XmotoFan]

Hi folks,

I've been trying to fix a wiring problem with my Xmoto for a while, that was causing the engine to randomly cut-out while riding - not good in the middle of an overtake! I've fixed one issue with a short related to the fuel pump but I'm now left with the following:

821: Speed sensor (rpm), signal implausible.
   This fault occurred 3 times.
   The fault is not present now.

This is after fixing the other problem and clearing the codes and then doing over 100 miles without any problems. Then the bike ran like a pig for a bit - surging nearly stalling, finally cutting out just as I got 100 yards from home. The bike restarted straight away. This same error was present before but I mis-read it as the wheel speed sensor, so I checked out that wiring.

Now I see it's the engine speed sensor and there appears to be an intermittent fault. Do these sensors fail in this way or is it most  likely to be a wiring problem?

Cheers,

Paul

[WayneC]

The crank sensor should measure around 300 ohms and they are generally reliable, they can get metal particle build up which causes problems but an implausible signal would tend to suggest a wiring problem

[XmotoFan]

Thanks for the info WayneC. I've checked the sensor and it's 239ohms. I remembered that I have a Haynes manual for the F650 (used to have one years ago) and that has 190 to 360ohms for post 2004 bikes, so on that basis the sensor looks OK. Do you agree?

I've also checked the wires from the sensor to the ECU and they are both about 0.5ohm which seems more than it should be but not excessive. I wobbled every moveable bit of wire around and the resistance didn't vary, so there doesn't appear to be any dodgy wires.

Don't really know what else to check. I am guessing that a metal build up on the sensor wouldn't show up as an intermittent fault, it would be progressive failure?

The bike has done about 32,000 miles. Coincidentally the alternator cover gasket is weeping a bit so I might pull the cover off anyway to fit a new gasket and check the crank sensor.

[WayneC]

Yes, would agree re the sensor and just checking it with the cover off, had a Xchallenge recently a BMW Dealer thought was the sensor but was frustrated in not being able to repair the beast so asked for assistance from a couple of us, we replaced the BSCII to repair it, looked like a little water had got into the BMSCII & a bit of residue had created some instability

[XmotoFan]

I've just removed the alternator cover and re-checked the resistance of the crank sensor. It was a bit different to yesterday at 242ohms. This made me wonder if it's temperature sensitive as it's warmer here today than yesterday.

So, I kept measuring resistance while blowing hot air from an old hair dryer. At 60degC the resistance went up to 275ohms. Does that sound like normal behaviour?

There's no metal debris on the sensor.

[WayneC]

All sounds fine, I would be looking for harness chafing then looking at what else may be a problem, cleaning throttle body, idle actuator etc