ABS Waveforms with the VP

[David Green]

Hopefully I can upload the graphs which I have produced on the VP

In the first example it can be seen that both the left hand rear wheel speed sensor and the right hand rear wheel speed sensor malfunction at the same time. In the second graph both rear wheel speed sensor circuits fail again at the same time, not shown just after the fault area is the immediate recovery which looks like the first graph starting from the left hand side.

I am thinking it is a faulty ABS ECM control unit, any views welcome.

David

I have been doing some more testing with the VP. The waveforms produced here I have really selected a voltage range too high. I am supprised that nobody picked up on this point and advised me? Just when I thought I had friends haha.

I selected a lower voltage setting and adjusted the ms throughout the range until I got the best graphs I could to fit the screen with reasonable accuracy. I would have uploaded these new files which are in movie format, but the SSC will not work with them so that's out I am afraid?

The new scope patterns don't look anything like the examples I posted here, nor do they look like some other posted by other members. I began to think that the VP was not up to it, then I said to myself surely snap on could not produce a scope that would not display a 'sign wave' graph?

A member on here posted me an example using the VP, it was a good example and clearly shows the VP is quite good at what it does when one knows how to set it up and interpret the signals received. My ABS wheel speed sensors compared across the same axle visually are very poor, they have spikes and glitches and varying voltage levels along their traces throughout, nothing like oberved on these examples posted by me here. What a difference it makes when the volt/div are lowered, now I know that at least two wheel speed sensors are needed, although only one registers faulty, the other will do if one new fitted I think based on the results of scope tests.

David

[Skip]

I would look for a common connector first. There may be corrosion built up affecting both sensors.

[vasau]

Looks like the VP was not properly grounded during the test. Where was the scope NEG lead during the test, grounded on the vehicle or the sensor?

[David Green]

Looks like the VP was not properly grounded during the test. Where was the scope NEG lead during the test, grounded on the vehicle or the sensor?

That's interesting, Where is the scope NEG lead during the test?

Having checked all the cables that arrived with the VP, the only lead that has the facility for grounding is the lead used for Ignition Pick up?

I understand the point that the VP may require a ground reference from the vehicle during testing, but with what lead?

David

[greasybob]

On the top of the Vantage Pro there should be a terminal (receptacle) marked "COM" And should be black, this is the ground. At least thats how my old Vantage is. Did the Vantage Pro com with a separate black ground lead or a combination shielded main lead.

[vasau]

When I was talking about grounding I meant that your VP scope must be grounded to vehicle negative terminal or vehicle body. You can even use any piece of wire if you do not have the original lead. OR you can use an external power source which will provide ground for the scope automatically using battery/cigarette adapter cable for example. That's what I do with my Modis.

[David Green]

Thanks for that info, the VP in the UK does not arrive with instructions on how to set it up and use it. I know some other Countries get a manual to help learn about the VP and its use.

I know about the ground plug in the top of the VP, but didn't understand how I was meant to ground the VP with the cables supplied when measuring sine waves for ABS sensors, I just used channel 01 and channel 02 and plugged a lead into each sensor at the ECM connector. Also the VP does not arrive with a power lead to connect to the CIG lighter or battery, so I assumed that snap on must have thought about this and understood that users would use the VP on the supplied batteries power only?

Some of the leads supplied and not readily understood as to their use, by example, one lead has a yellow and black lead which go into a black connector, then three wires come out of this black connector on the other side, I think one is channel 01 and one is channel 02, and the remaining black lead is the ground?

However I don't know the correct function of this lead because it is not clear where the third lead has gone or what it does because it does not come out of the black connector, therefore what I am saying is;

Three leads into the connector from the VP, and two leads out to the vehicle for testing purposes?

I checked the continuity with a meter and two black leads have continuity, and also one black lead with the yellow lead?

David

[greasybob]

The second black lead on the scope end is the shield wire and you should be able to stack the two on top of eachother and plug into the "com" terminal. The black lead on the test end is the ground and should be attached to a good chassis or directly to the battery ground.

[greasybob]

maybe this link to the user's manual will help if it works over there http://diagnostics.snapon.com/vp otherwise just enter the address there is a user manual on pdf there

[JR-1]

David , you have 2 scope leads , for example ch1 is yellow black , yellow to component ...black to earth .Second channel (green)in operation you will use the piggy back earth so ch2 can use that earth . The only problem i have is leads are way too short .I know of some who use the fluke leads as extensions .As far as information goes the lik provided should get you going and als there is help menu's in the vp .

HTH
John

[vasau]

Thanks for that info,...

You are welcome.
I have never used Snapon scope leads, they are not good for everyday use. For portable tests I have bought a couple of those leads at the site an marked them with a colored tape. http://aeswave.com/Products/Product.asp?i=246
Those leads are not shielded like special scope ones and you have to keep them away of engine components such as alternator, coils e.t.c.
I also use the 10ft special Modis scope lead set on my workstation cart bought at the same website.

[David Green]

You are welcome.
I have never used Snapon scope leads, they are not good for everyday use. For portable tests I have bought a couple of those leads at the site an marked them with a colored tape. http://aeswave.com/Products/Product.asp?i=246
Those leads are not shielded like special scope ones and you have to keep them away of engine components such as alternator, coils e.t.c.
I also use the 10ft special Modis scope lead set on my workstation cart bought at the same website.

Thanks for the additional information, yes I have been moaning about the lengh of the leads, in mobile use when connected to an ECM (PCM) under the bonnet (Hood) location the VP is difficult to settle inside the vehicle being tested, so yes I will have some longer leads on order.

[David Green]

The second black lead on the scope end is the shield wire and you should be able to stack the two on top of eachother and plug into the "com" terminal. The black lead on the test end is the ground and should be attached to a good chassis or directly to the battery ground.

Hi greasybob,

Hope I am reading you correctly here, please let me explain what I have just tried with the leads and advise if you think I am right?

Yellow and Black lead; Connected Yellow lead into channel 01. Black lead into Common. Test Ends of leads; Yellow to sensor and Black to ground.

Green and Black lead; Connected Green lead into channel 02. Stacked the Black lead on top of the Black lead from the Yellow lead.

Now as there are TWO Black leads from the connector of the Yellow lead, and as explained above, one is already in the Common plug of the VP, I have now Stacked the remaining Black lead also into the Common on the VP, thus I have three Black leads now into the Common.

For measuring purposes; I have a Black lead going to vehicle ground. I have a Yellow lead to measure channel 01, and a Green lead to measure channel 02.

How am I doing guys

David

[JR-1]

David , why have you got 3 earths for 2 channels?

[greasybob]

If you have two leads, then you should have three grounds stacked. The yellow lead has two grounds , one is the scope ground and the other is the shield ground. The second lead is has just a shield ground. the purpose of grounding the shield wire is to diffuse or reroute any interference it picks up back to the chassis ground so you get a clearer reading on the scope. The green lead does not require a second ground since the scope only needs to be grounded once. Hope this clears things up.