rover 25 p0722

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rover 25 p0722

Postby Neilcur » Tue Feb 26, 2013 7:48 pm

Hi folks, This is going to be first proper go at using scope so need some help. Got a rover 25 in throwing up a p0722 code for automatic transmission output speed sensor fault, symptoms are car drives fine up to 55mph but if you cruise at that speed the car will sometimes go into a limp home mode the ecu puts the auto box into a low gear and puts an auto box warning light on dash and you have to rev car to get it off road. Car came to us after being at another garage who have checked the wiring and replaced sensor etc but when i had car on ramp looking for sensor i noticed speedo drive was new so i think they have replaced wrong sensor. Not got alot of live data readings with diag tool so was going to scope sensor while driving and see what is happening rather than just fit a new sensor as customer has spent quite abit of money elsewhere trying to fix problem already. My question is should i just scope signal wire on its own on a long time base during test drive so i can zoom in once fault occurs or should i do something else? It's a 3 wire sensor, volts/signal/ground will i gain anything from scoping other 2 wires aswell at same time?

Any help would be great

Thanks Neil
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Re: rover 25 p0722

Postby mteste03 » Tue Feb 26, 2013 9:01 pm

Hi,

Maybe worth connecting to all 3 wires as if you lose the signal during test drive you can at least confirm if power and grounds remainded ok.

Matt
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Re: rover 25 p0722

Postby AuthorMike » Wed Feb 27, 2013 9:09 am

I agree with Matt, I would scope all 3 wires. Also, if you are working on your own definately set a long timebase, or of course take an assistant with you to operate the scope/software!

Either way, post your findings... perhaps you could create a Case Study ;)

Always good to hear of experiences whether from a new user or experienced one!


Mike
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Re: rover 25 p0722

Postby Neilcur » Tue Mar 05, 2013 2:36 pm

Hi, took the rover a run today and got it to falter while the scope was capturing and the signal is dropping out and the earth and supply is good so just wanted to put the data on here to make sure thats the case before i order a sensor. the signal at end was me turning key on and off a few times.

Thanks Neil
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ROVER25AUTOSPEEDSENSORBAD.psdata
(721.45 KiB) Downloaded 235 times
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Re: rover 25 p0722

Postby AuthorMike » Tue Mar 05, 2013 4:04 pm

Hi Neil,

I've downloaded this to look at but havent had a proper look. Will get back to you in the morning with more info....

The signal wire... looks interesting... especially when zoomed...can you repeat the test over less time? The length of the trace (8minutes) combined with the sample rate (which is OK) equate to less than 2000 samples a second., so less time will equal a clearer capture.


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Re: rover 25 p0722

Postby Neilcur » Tue Mar 05, 2013 4:18 pm

Hi,

Took the car a run and the fault occured straight away so stopped waited 5 mins and started and drove back to workshop and fault didnt occur and i captured that aswell which i have attached below, so could we use this as a good capture? Its also on a long timebase but if you require it re-done with a shorter timebase etc i can redo it.

Thanks Neil
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ROVER25AUTOSPEEDSENSORGOOD.psdata
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Re: rover 25 p0722

Postby AuthorMike » Wed Mar 06, 2013 9:56 am

Hi Neil,

I've done some digging this morning...(I would like to add I am not "Technical Help" here at Pico)...

From the web...
"P0722 is for Output Speed Sensor 2 Circuit No Signal. This means that the transmission control module is not receiving a signal from the Output Speed Sensor. There is a possibility it could be the Neutral safety switch. They can get dirty and cause problems."

Testing Neutral Safety Switch

Required Tools:
Test Light/Voltage-meter/Scope
Wiring schematic
Neutral safety switch location (component location)

Test Procedure
Locate the neutral safety switch
Disconnect the wiring connector at the switch
Test for power at the wiring harness with the key in the "engine crank" or the gear shifter in the "reverse" position. (do not start the engine)
If power exists reconnect the neutral safety switch and probe outgoing wires at the connector.
If no outgoing power is present the switch has failed and needs to be replaced.
If the engine will not crank over with the car in "park" push down the brake pedal and try cranking the engine over with the car in "neutral". What you are doing is bypassing the "park" position in the switch and now are using the little used neutral circuit. If in neutral the engine starts the switch is probably bad.
Tip: Sometimes a neutral safety switch can become misadjusted. This switch adjustment can change due to normal wear of mechanism that controls switch slider.
Other complications can occur if there is a loose connection somewhere in the system. While this condition is not a shorted circuit problem, it is a condition that simply breaks the flow of electricity intermittently.

Also an interesting article here - http://www.underhoodservice.com/issue/a ... tid=105757


I believe we should be seeing a square wave (hall effect) from your sensor (from the above article as you have 3 wires I am guessing its a 'MagnetoResistive Sensor'). Currently it looks more like a camshaft signal....

I think a shorter test will provide a better sampling rate across the screen and therefore we should see a square wave signal,....

There is clearly 55 seconds of "faulty signal" in your bad waveform...but identifying the cause for this is important.
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Re: rover 25 p0722

Postby Neilcur » Wed Mar 06, 2013 6:45 pm

Hi Mike,

Thanks for info, not had a chance to get back to car yet but i have had a read through that article and i am not seeing a square wave through out the whole capture as you said, but it also isn't a square wave in my 'good' capture the whole way through so not sure if this is a bad sensor or the way i have captured the event or a bad pick up inside the box. Was hoping some of the other guys would put some suggestions forward but i know they are busy with there own work and don't have the time to follow this thread step by step, will try and get another capture on a shorter time base and see what the results are.

Thanks Neil
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Re: rover 25 p0722

Postby KimAndersen » Wed Mar 06, 2013 9:38 pm

Hi

Where did you measure the signal from the output speed sensor - at the sensor itself or at the ECU ?

Regards
Kim
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Re: rover 25 p0722

Postby Neilcur » Wed Mar 06, 2013 9:41 pm

Hi

I measured the sensor at the multi-plug as i couldn't find a decent rover wiring diagram to see where signal wire goes. I had a look on autodata today and it seems to go to engine ecu so not sure how it gets signal from there to TCM maybe just wired straight to it but would rather find a proper wiring diagram to make sure as sometimes autodata's wiring diagrams do not match up.

Thanks Neil
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