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Phil
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Discussion Starter · #1 · (Edited)
Ecu fault codes tell me that there is a problem on both the rear wheel speed sensors - yes, both of them. And they won't clear down even using MUT 3.

The background is that all four wheel speed sensor cables have recently been disconnected at the respective first connector blocks, two in the engine bay (for the fronts) and two in the boot (for the rears). None of the actual sensors were removed from any of the hubs.

After re-connecting the four sensor cables there were four separate fault codes present, but after re-setting all four codes the two the codes the two for rears have persisted.

Simply buying a pair of new rear sensors is of course an option, but they are over £350 each so not a decision to be taken lightly!

And in any case I am extremely suspicious that there really is anything wrong with the sensor and their leads. If a single sensor had gone down I might have accepted that, but unless lightening really can strike the same place twice, I'm extremely sceptical that both could fail at the same time.

So my next step is to find a way to perform an electrical test on the "faulty" sensors and compare the readings with readings from a "known good" one. But the question is what and how to test and what measurements should be taken?

On the Evo X my understanding is that the wheel speed sensors (WSSs) are of the "active" kind, so the car does not need to be moving for any problems to be detected. Also that they do not exhibit a resistance reading if an ohmeter is placed across the pair of pins in the connector block. And the final thing is that during periods when the ignition is on, the sensor is supplied with battery voltage.

What else can I/should I test?

The other thing that I found out about the Evo X is that it does not have the regular kind of toothed ring on the drive shaft that the WSS sensor sits in close proximity to, but rather that there is the equivalent of this ring built into the bearing assembly. Has anyone ever heard of this part of the system failing?

Any help would be appreciated:)
 

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Phil
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11,023 Posts
Discussion Starter · #3 ·

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Phil
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11,023 Posts
Discussion Starter · #5 ·
probably obvious but have you checked for continuity between either side of each of the joining pins across the joined connectors, just in case

Stu
A poor connection (at the connector) has not specifically been ruled out, nor that there might be a break in cable. But the main mystery (to me) is explaining how two sensors could possibly gone down at the same time. Surely it's too much of a coincidence that they both develop faults when essentially all that's happened is that they have been disconnected and then reconnected.
 

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Premium Member
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A poor connection (at the connector) has not specifically been ruled out, nor that there might be a break in cable. But the main mystery (to me) is explaining how two sensors could possibly gone down at the same time. Surely it's too much of a coincidence that they both develop faults when essentially all that's happened is that they have been disconnected and then reconnected.
agree but, testing doesn't seem simple, so ruling out the simple surely has to be a start. Daft as it sounds i'd also try removing the battery for an hour or 2 too. Again, probably a waste of time, but costs nothing and is no effort to try

Stu
 

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Phil
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11,023 Posts
Discussion Starter · #7 ·
agree but, testing doesn't seem simple, so ruling out the simple surely has to be a start. Daft as it sounds i'd also try removing the battery for an hour or 2 too. Again, probably a waste of time, but costs nothing and is no effort to try

Stu
Testing the connector cables for continuity isn't easy either, and I don't really want to probe the wires and create even a tiny breach that could give rise to issues in due course o/a corrosion. But again, why both sensors registering a fault? I'm half inclined to think it could be the wheel signal sensor processor unit that's at fault rather than the sensors.

As you suggest, no harm in seeing if a battery disconnect would make any difference.
 

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Premium Member
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yep, that was why I mentioned the plugs rather than the wires, I havent seen the plugs (in fact I know sweet F.A. on a 10 :lol: ) but thought maybe the plugs maybe easily continuity tested

Another option must be to get a copy of the workshop manual and see if there is anything mentioned for replacing wheel speed sensors, a learn process maybe

Stu
 

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Phil
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11,023 Posts
Discussion Starter · #9 ·
yep, that was why I mentioned the plugs rather than the wires, I havent seen the plugs (in fact I know sweet F.A. on a 10 :lol: ) but thought maybe the plugs maybe easily continuity tested

Another option must be to get a copy of the workshop manual and see if there is anything mentioned for replacing wheel speed sensors, a learn process maybe

Stu
It's been on a MUT 3 and there was no indication of any kind of learn process. And I don't think the kind of sensor on an active system would give a continuity signal across the pins at the connector?

Maybe I should add that the car in question is a X RS which doesn't have ABS, so the wheel speed sensors are needed purely for the ACD.
 

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It's been on a MUT 3 and there was no indication of any kind of learn process. And I don't think the kind of sensor on an active system would give a continuity signal across the pins at the connector?

Maybe I should add that the car in question is a X RS which doesn't have ABS, so the wheel speed sensors are needed purely for the ACD.
Im only throwing guesses at you as there arent many other replies.Hopefully some of the traders may shed some light on this tomorrow :smthumbup

Stu
 

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Premium Member
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Both rear sensors on my 2009 X with 20k miles packed up recently. One side went first then 4 months later the other rear side packed in. I had ABS sensor warning.. As you say not cheap some 550 plus fitting for both rears.
 

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Phil
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11,023 Posts
Discussion Starter · #13 ·
Both rear sensors on my 2009 X with 20k miles packed up recently. One side went first then 4 months later the other rear side packed in. I had ABS sensor warning.. As you say not cheap some 550 plus fitting for both rears.
Do your have any idea what was wrong with them? Did fitting new instantly cure things?
 

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Phil
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11,023 Posts
Discussion Starter · #14 ·
before I bought sensors i'd definitely be doing continuity across the plug, even if that means damaging the seals, as that really is what has been disturbed.

Why were they disconnected?

Stu
Disconnected because the hubs were removed, but with the sensors still installed.
 

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Premium Member
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Yes, I've done some 200 miles since they were replaced recently and all seems fine.

Nope they were not disconnected prior to failure.

Didn't really investigate any other sources of failure. Had Warning lights in the dash, diagnostic read the fault code and we replaced one side then a few weeks later the other side did the same.

All seems fine now after replacing sensors.
 
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Premium Member
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Are both sides registering the same fault for both sensors? Or do they each have a different fault to each other? High resistance, open circuit etc?

Cheers Aj
 

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No idea of the exact spec of that fault codes. Speak to indigo GT they read the codes and replaced both sensors for me.
 

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S.Wales R.O./Electrician
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4,126 Posts
What fault codes are you getting?

Pinning out the sensors at the ECU plug for resistance won't damage anything and will tell you whether the sensors themselves are ok.
 

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Phil
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11,023 Posts
Discussion Starter · #20 ·
Latest on this is that some 'known to be good' sensors have very kindly been provided and these have been put in circuit and the faults are still showing. So now the hunt is on for why the sensor signals aren't being received/processed correctly.
 
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