Speedo Sometimes Stops And Shaky Engine Brake

[mako]

my xm (mk2, v6 24v) has a problem as belows

speedo sometimes suddenly goes down to zero, at the sametime the engine brake jolts.

I have replaced speedsensor twice, but resulted in vain.

Is there anyone who can suggest any resolution?

This post has been edited by mako on April 24, 2010 04:13 am

[DerekW]

Hi Mako, does your cruise control still work OK? If so, then the signal from the speed sensor must be getting through. In that event I'd be inclined to check the multiplug at the speedometer, it's fairly easy to get to.

Derek

[noz]

Hi Mako,

I think the problem with your speedo may be solved here:
http://club-xm.com/forum/index.php?showtopic=2803&hl=speedo

I'm not sure I understand what you mean by "the engine brake wobbles". Can you explain more clearly what that means?

Cheers

noz

[mako]

Hi, dereKW
Thanks for your comment, I will try the cruise control on motorway in a few days.
But worried about what will happen to cuise control with incorrect information "speedo is o", I hope the car would't run out of control.

Hi, noz
Sorry for my awkward English,
Engine brake wobbles...
I mean the braking(deceleration) effect comes from release of accelerator pedal.
this jolts as long as the speedo indicates "o km/hr". But when I step on accelerator, the engine stops jolting.
Probably, I assume that ECU for fuel injection gets confused because of incorect speed information.

have replaced speedsensor twice, but resulted in vain.

Now I'm wondering what to do next.

This post has been edited by mako on April 23, 2010 03:59 pm

[noz]

Hi Mako,

Don't worry your English is absolutely fine.

I don't recognise the connection between the faulty speedo and the jolting of the engine. If the two are connected I will have learned something new.

The road speed data is collected by one sensor on the gearbox. The cable rises from the sensor and reaches a joint in the cable with a white plug and socket. The plug is located below the LHM reservoir. After the plug the cable travels across the bulkhead towards the ecu. Just before the ecu there is a joint hidden in the cable insulation. One branch goes to the engine ecu and the other goes to the suspension ecu.

http://club-xm.com/forum/index.php?showtopic=2103

You need to establish if the sensor is faulty or if there is a break in the cable between the sensor and the ecu's.

cheers

noz

[mako]

Hi, all
I realized that I have replaced the crank sensor, not speed sensor.
I have just replaced the speed sensor, and will check if the speedo falls again.

sorry for noise.

[noz]

Hi Mako,

Aha, that makes a lot more sense now. A faulty crank sensor would indeed cause the engine to jolt. However, there's no connection between the crank sensor and the speed sensor.

I hope that by replacing the speed sensor this solves your problem with the speedo. If not, the previous two links above should help.

Cheers

noz

[mako]

Hi, all

sorry for forgetting to report the result.

All problems have dsappeared just after replacing with the "correct" speed sensor, including engine jolting with engine braking.

I have seen no problem with them for about a year.


thank you for kind suggestions, derekW and NOZ.

This post has been edited by mako on March 11, 2011 04:14 am

[noz]

Hi mako,

No problem. I'm always glad to hear of a successful repair story.

Cheers

noz