Login | Register
SearchMy Stuff
My ProfileMy PreferencesMy Mates RSS Feed
Reply to Topic
Author Discussion

DZ300

Original Poster:

65 posts

82 months

[news] 
Thursday 14th May 2009 quote quote all
'Ello all!

I should never have said out loud that my wife's MX5 has been running faultlessly for the past 4 years because almost immediately after I said it the ABS warning light came on.

Strange one this as it is very intermittent. Sometimes the warning light remains on after I first start the car up (presumably there is an ABS self-check function that happens when the ignition is switched on). Other times all is fine until later on in the drive when the light spontaneously comes on. On other occasions it turns off if I stop the car, turn off the ignition and restart the car. Very strange indeed.

So far I've checked the following:
1. ABS connectors at the wheels
2. ABS connectors in the engine bay
3. Fuses
4. Tyre pressures
Everything seems fine.

I've been in contact with Sam Goodwins up in Nuneaton but they (obviously) can't diagnose the problem over the phone and apparently haven't got a diagnostic kit to plug into the car. I'm a bit reluctant to take it to our local Mazda dealer (Brooklyn's of Redditch) as they are likely to charge an arm, leg and kidney for hooking the car up to their diagnostic equipment and then still have no clue as to what the problem is.

So, I thought I'd ask here if anyone else has had this problem or whether anyone knows what it is like to be.

Many thanks for your feedback.

Regards,

Dan

OnlyMX5ives

1,141 posts

79 months

[news] 
Thursday 14th May 2009 quote quote all
What yr is it ?

DZ300

Original Poster:

65 posts

82 months

[news] 
Thursday 14th May 2009 quote quote all
Sorry, forgot to mention that it's an August 1998 Mk2 1.8iS (UK car)

Munter

25,370 posts

128 months

[news] 
Thursday 14th May 2009 quote quote all
My MK1 did this for a while. Some times the ABS light would come on. Eventually it stopped. And I've no idea why.... Possibly the bulb burnt out. But More likely I'm told is some kind of dirt on the "toothed" part of the hub/sensor that eventually came off.

Can you get underneath and see if theres a suspicious ammount of dirt around the hub/abs sensor....

DZ300

Original Poster:

65 posts

82 months

[news] 
Thursday 14th May 2009 quote quote all
I'll have another look but when I last checked the abs connectors at each wheel I don't think I saw an excessive amount of dirt. Thanks for the tip! smile
Advertisement

OnlyMX5ives

1,141 posts

79 months

[news] 
Thursday 14th May 2009 quote quote all
Sam Goodwins can't read codes laugh

You only need an LED and a bit of wire !

However I'm 90% sure ABS faults aren't logged (not many had ABS) I can check tomorrow but no doubt someone will have a book to hand.

Its usually a dodgy sensor though.

bluetone

2,040 posts

106 months

[news] 
Thursday 14th May 2009 quote quote all
A 1cm square of black tape should sort that problem out nicely.

DZ300

Original Poster:

65 posts

82 months

[news] 
Friday 15th May 2009 quote quote all
@ Bluetone & OnlyMX5ives: Can you elaborate on the LED/wires procedure and also the black tape?

I'm not too concerned about driving the car as I've tested the brakes (with the ABS light on) and everything seems to function as it should.

Thanks again for your feedback so far!

Regards,

Dan

bluetone

2,040 posts

106 months

[news] 
Friday 15th May 2009 quote quote all
DZ300 said:
@ Bluetone & OnlyMX5ives: Can you elaborate on the LED/wires procedure and also the black tape?

I'm not too concerned about driving the car as I've tested the brakes (with the ABS light on) and everything seems to function as it should.

Thanks again for your feedback so far!

Regards,

Dan
Ahhh, perhaps I should have put a winky-smiley on my post as it was meant to be a joke (a poor one I guess) = put the black tape over the ABS light....

wink

Gustavo

11 posts

68 months

[news] 
Friday 15th May 2009 quote quote all
I have got pretty much the exact same problem as the OP describes. Same model of car, same year, and same ABS light problem. Sometime it is on, others it isn't. I have been round and cleaned all the sensors and it made no difference.

I assumed that a sensor must have been on the way out, so sent it to a garage for a diagnosis (was due for service / MOT)...
...turns out that despite the light being on there was no fault registered by the onboard diagnostics. All four wheel speed sensors were working correctly. Furthermore, not only was the diagnostics not showing a fault, it also stated that the ABS light was off, when it was clearly illuminated!

The conclusion that the guys in the garage came to was that it was a poor earth connection somewhere that was sending power to the ABS light, despite the ECU not detecting a fault. There are full wiring diagrams for the 1999 Miata floating around the internet (should be more or less the same as the UK mk2 1.8iS I'd have thought), so it should be possible to ascertain whether a wiring fault can cause the ABS light to illuminate - I've just not had time to sit down and study them since I got the car back from the garage.

I imagine that most ABS faults are caused by sensors dying, but apparently mine (with a near identical car to the OP's) wasn't. If you do a search on the MX5 Owner's Club website there are a couple of threads about ABS problems, and in one of them the allowable resistance of the wheel speed sensors is quoted. This might help with some basic diagnostics...

I'm not sure what the lesson here is, but hope it helps!

DZ300

Original Poster:

65 posts

82 months

[news] 
Friday 15th May 2009 quote quote all
Hi,

LOL @ the black tape over warning light! smile I should have seen that one coming! smile If all else fails I'll take that option.

@ Gustavo: Thanks for your comments - it has given me another angle to think about. I suppose an intermittant earthing problem could cause a warning light to come on without the diagnostic unit knowing about it. I'll have a close look at all the wiring this weekend (if it stops raining long enough).

I've just been on the phone with Brooklyn Mazda in Redditch and they would like me to part with £99 + VAT and an hour of my time for the privilege of hooking up the car to their diagnostics unit! Nearly fell off the chair when I heard the good lady confirm the price ... Don't think they'll be getting my business.

So, the search continues for somewhere that can read fault codes. Having looked around on the interweb I understand that MK-2 cars are not OBD-2 equipped (the proprietary connector under the bonnet kind of gave it away). So what protocol does it use and can I get a (inexpensive) scanner to hook up to it? I've looked at www.talktomycar.co.uk but they couldn't confirm whether any of their scanners would connect up correctly.

At this point in time I'm open to any suggestions as to (a) where to take the car to have it diagnosed or (b) where to buy a scanner myself. Any and all feedback gratefully received as always.

Many thanks so far to everyone who's contributed to this thread. I will get to the bottom of this problem but I refuse to fork out that kind of dosh to a Main Stealer!

Regards,

Dan

OnlyMX5ives

1,141 posts

79 months

[news] 
Friday 15th May 2009 quote quote all
Whilst I have never had an ABS problem to solve...

The std MX5 codes are simply read with an LED. MX5 Parts used to sell a booklet but many manuals and various web sites also tell you how to do it.

I'll happily read anyones Mk1/2 MX5 codes for a fiver !

However after looking in my book it says (as I thought) that there are no ABS codes.

Now perhaps the ABS has its own system (It has its own ECU) but I'm unaware of being able to communicate with it. A previous post suggests someone can and as I say I've never looked into it but as its a pretty old design I suspect that you can't and you need to rely on good old fashioned 'mechanicing'.


bluetone

2,040 posts

106 months

[news] 
Friday 15th May 2009 quote quote all
OnlyMX5ives said:
Whilst I have never had an ABS problem to solve...

The std MX5 codes are simply read with an LED. MX5 Parts used to sell a booklet but many manuals and various web sites also tell you how to do it.

I'll happily read anyones Mk1/2 MX5 codes for a fiver !

However after looking in my book it says (as I thought) that there are no ABS codes.

Now perhaps the ABS has its own system (It has its own ECU) but I'm unaware of being able to communicate with it. A previous post suggests someone can and as I say I've never looked into it but as its a pretty old design I suspect that you can't and you need to rely on good old fashioned 'mechanicing'.
Indeed, I made one of the resistor and LED in-line contraptions to read a fault code on my Mk1 a while back. I'd never even used a soldering iron before (and got the burns to prove it LOL).. The LED thingymajig worked a treat though smile

DZ300

Original Poster:

65 posts

82 months

[news] 
Tuesday 19th May 2009 quote quote all
Just a quick update:

Many thanks to OnlyMX5ives for taking the time to check the fault codes this afternoon. None were stored so in a way that is good news. We'll now wait until the warning light comes on permanently before starting to swap parts out until we find the culprit.

So it would seem that ABS fault codes can not be pulled using the diagnostic plug under the bonnet. Would be interesting to find out if anyone could interrogate the ABS ECU and pull codes off it.

Thanks again for everyone's feedback!

Regards,

Dan

Gustavo

11 posts

68 months

[news] 
Monday 25th May 2009 quote quote all
I've had a bit more of an investigation into the ABS system and the now perminant indicated ABS fault on my car, same model as that of the OP. A full explanation is below, if you're bored / interested, but to cut a long story short I'm now 99% certain that one of the front ABS sensors is to blame.

The ABS light in the instrument cluster is supplied with power whenever the ignition is on, and then is connected across the dashboard to the ABS ECU below under the passenger footwell. The ABS ECU then decides whether to ground this connection or not - in the case that all is working correctly the connection is not grounded and the circuit containing the ABS light is not completed.

The garage that looked at my car suggested that a dodgy ground was occuring that meant the ABS light circuit was completed regardless of what the ABS ECU thought. As far as I can see this can only occur after the ABS light and before the ABS ECU - ie, somewhere behind the dash. I pulled the passenger footwell apart to get at the ABS ECU (not an easy task because the cover over the ABS ECU is fastened with two shear bolts - no heads mean hammer and chisel required) and located the signal wire from the dash (pink / black). I then took all the driver's side of the dash apart to get at the connector and locate the other end of the signal wire. When the signal wire was cut, the ABS light did not illuminate, which proved that there was no grounding problem in the instrument cluster. I then tested the wire itself by connecting a new piece of wire in its place. This time the ABS light remained on, which proved that there was no grounding problem in the wire (or if there was there was also an ABS fault).

I then started to get a feeling that my initial suspicions about a wheel speed sensor being the problem were re-awakened. I then compared the resistances of the two front sensors. One was reading around 1800 Ohms, the other was right off the high end of the scale. As a quick check I ran a couple of pieces of wire across the car and wired the signal from the sensible sensor into both front sensor loom connections. This made the ABS light go out, which leads me to believe that the sensor with the massively high resistance is the one and only problem.

A few hours and some expletives later and the bad sensor was out of the upright and off the car (I hope mine isn't the only MX-5 where every suspension bolt is undone by first either rounding or shearing off the head and then drilling out the remains!?!?). I'm locating a replacement now - when I've fitted I'll let you know if the problem is cured.

Hope this helps with your ongoing diagnostics - although this kind of approach only works once an intermittant problem has turned into a perminant one!

Jonny671

27,706 posts

76 months

[news] 
Friday 18th June 2010 quote quote all
Thanks for the post Gustavo!

I'll tell my techs to have a look at that on mine smile

Thread from the dead! biggrin

DZ300

Original Poster:

65 posts

82 months

[news] 
Saturday 19th June 2010 quote quote all
Ooohhhh, a thread from the dead - I love it! ;-)

I had forgotten about this thread so thanks for bringing it back up.

Just to complete the story of our saga, the problem was resolved by replacing the driver-side ABS sensor. How did I get to that? Well, it turns out that you CAN read the ABS ECU fault codes. I took the car up to Nottingham (5Speed) and he had somebody read the codes. Had to save some pennies but eventually ordered a genuine Mazda ABS sensor through MX5Parts and replaced it myself - beware, getting the connector through the wheelarch liner and to the correct place is a real PITA. Once the install was completed the ABS light on the dash no longer lit up and all has been well ever since! :-)

Unfortunately the next (unrelated) problem has reared its head: brake imbalance ... Oh well, if I can't tinker with the car I don't think I'd be too happy.

Thanks again to everyone who contributed valuable input.

All the best,

Dan
Reply to Topic