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On going ABS problems...


rekab69
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I won't bore you with the history of this but rest assured it's been going on for years, on & off. 1998 110 Td5.

Replaced modulator, sensors front & rear, bled brakes with lap top, and manually...

Rebuilt hubs, balanced wheels,wiring, check position of sensors.... etc, etc...

Yesterday while bleeding the system for the umpteen time, I noticed low voltage 11.40v registering for the battery.

I had up until that point managed to get to the point where once the ignition was turned on the ABS light would flash once and stay on, TC light would go out.. Great..!!

Start engine, as above, still great, drive over 5mph ABS light would also go out, dancing in my seat now...!!

Drive around, all speeds, fine. brake once both come back on... NOT Great..!!

I though maybe battery voltage could have an effect.. Charged battery all night, fully charged..

Put it back on BOTH lights on, did not go out when engine started, I'd only removed and replaced the battery and this too has an impact...!!

On test drive, both went out but not individually as they should... Touch the brakes and on they both come...

Now this is the weird part.... If i keep the revs high and brake they stay out, they only come on if I let the engine drop down to idle as it does when coming to a halt.

Brake when the engine is reving all is fine, brake when the engine is at idle they pop back on....??

At a loss...

db.

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have you tried another ABS ECU as that controls the dash ABS & TC lights according to my td5 wiring diagrams.

copied from my RAVE cd.---------------------

DESCRIPTION AND OPERATION
4.16 DEFENDER 1999 MY
Instrument pack
The ABS ECU will inform the driver of any faults within the ABS or traction
control systems (if fitted). The ABS ECU (C0504-9) supplies a feed to the brake
fluid warning lamp (C0230-14) on a black/white wire if the level of fluid in the
brake fluid reservoir reaches the minimum mark. The warning lamp (C0230-8)
is earthed on a black wire.
If the ABS ECU detects a fault within the ABS system, it supplies a feed
(C0504-18) to the ABS warning lamp (C0230-7) on a red/slate wire. The
warning lamp (C0230-8) is earthed on a black wire.
If traction control is fitted, the ABS ECU (C0504-17) will illuminate the traction
control warning lamp (C0230-16) by providing a feed on a yellow/slate wire if a
fault is detected. The warning lamp (C0230-8) is earthed on a black wire.
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Hi Ralph,

Yes, I have also changed the ABS ECU this comes under the Etc, Etc, in my list of things done... New reservoir top too.... Shuttle valve switch upgrade... as well..

Thanks for the RAVE info, I will check the Earths, today I will also check the voltage from my battery as I think it could just be volts related as the alternator will be pushing out higher volts with high engine revs...

Guess if I just fly around heal & toeing, and left foot braking it will be fine... HoHoHo...

Thanks,

db.

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Guess if I just fly around heal & toeing, and left foot braking it will be fine... HoHoHo...

not if you end up in a hedge somewhere. :blink::wacko: that'll spoil your whole year.

going back to my wiring info, the ABS system Earth header is C0550, located in centre of bulkhead engine bay side, could be dirty/corroded header causing the problem, it's a light grey case hiding behind the coolant header tank & below the inertia switch.

happy cleaning.

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Ditches are ok as I know of a good recovery Man..

Earth C0550 is good... Just road tested it again... Defiantly only come on when braking with engine at low revs, keep the revs up while braking both lights stay out....!

Left my multimeter round a friends, going to check battery volts and swop the battery too...

Thanks. db..

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It may be a long shot but - change the brakelight bulbs/clean the wiring and connections in the bulb-holders.

Bizarre, Volvo-main-dealer-perplexing ABS behaviour in a friend's XC90 (spit!) was eventually solved by draining the cupful of water from the nearside rear light unit, cleaning/drying out the connections and reassembling with new bulbs!

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Disconnected rear light completely by unplugging the connections... No joy... New light units / bulb holders too...

"I had managed to get to the point where once the ignition was turned on the ABS light would flash once and stay on, TC light would go out.. Great..!!

Start engine, as above, still great, drive over 5mph ABS light would also go out, dancing in my seat now...!!"

It won't even do the above now and all I did was remove the battery and charge it up... BOTH lights on up until 10mph then they BOTH go out, then on again when braking... they are working together now, ganging up on me I feel...!!

What could be affected by just charging the battery...?

Thanks..

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Have you measured the earth path from the ECU to the battery with a multimeter?

Hi elbekko,

I put a multimeter across from the battery neg terminal to the bolts / black cable / brown cables going into the ABS ECU, I had the meter set on audio continuity.. It beeped continually.

As for a reading I could do with some advice as to what it should be and where exactly to measure it at...

Thanks,

db.

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measure voltage.

If theres a good earth path, it will read 0v.

if theres a poor earth you'll get some voltage across it.

Can you get a diagnostic reader for these ABS units? If so, you should look to asking it why its bringing the light on! Its probably logged a fault code about whatever its not happy with!

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Hi Aragorn, it's been on my local independent L/Rover garage's diagnostic machine more time than we can remember over the last few years, poor guy said at one point he was even dreaming about my ABS problems... It always came up with right hand front wheel sensor....

So.. checked resistance of the sensor... 1.9 0r 0.9 ohms can't recall it at the moment but it was near enough, install a new sensor anyway. replaced the wiring right back to the ecu too. Made a bracket to hold the sensor in place incase it was being knocked out of position, stripped the hub down to check for any wear or play.... All good..

It's had new rear sensors too...

So intermittent that it would go out for weeks, then pop back on... it got so I just lived with it being on..

The reason I need to finally get it cured once and for all is I have a new 110 well new to me and I plan to sell the old girl but I can't sell it with an ABS light on, needs an MOT too.. In the past it came on once, on the way to be MOT'ed I told the tester that it was on, he said lets have a look.... No lights on, new MOT... came back on about a week later..

I'll check for voltage in the morning, may even go and get the codes read again too..

thanks for you help..

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While we all love to hate electronics, their self diagnostics are one of the most useful features. Having the kit to immediately be able to scan the ECU, clear codes and see what has come back etc, is pretty invaluable when trying to diagnose an issue like this.

If it says its the front right ABS sensor, and thats the only fault code, then its either the front right sensor, or something is making it think the front right sensor is faulty.

On the ECU's i've dealt with, most of the codes have a "sub-code". So for instance you will get front right sensor, open circuit, front right sensor, short circuit, front right sensor, implausible signal.

Many people will overlook this, but if the ECU does provide these sub codes they can provide a good insight into whats happening.

For instance if its an "open circuit" code, then you can immediately rule out mechanical stuff like CV joint reluctors and wheel bearings, because the ECU's telling you that the electrical circuit itself is the issue. It could ofcourse still be a bad sensor with an internal break, or a wiring issue.

However if its implasuible signal, that often indicates that the circuit wiring and sensor are probably fine (otherwise it'd be flagging an electrical code instead), but it IS some sort of mechanical issue, like a bad reluctor or incorrect sensor gap causing the signal the ECU's seeing to not-look-right in some way.

On the bosch 5.3 system used on my daily driver theres another aspect that causes issues. The ECU for the ABS system is mounted onto the pump itself, and inside the ECU there are tiny thin bond wires connecting the PCB to the electrical connector. These bond wires break, most often in such a way that shuts down the whole system, but occasionally in a manner which causes it to think one particular sensor is dead.

So if it really isnt the sensor, then the only thing left is the ECU thinks the sensor is faulty due to some internal fault. Given it appears to be perhaps voltage influenced, that might well be an ECU fault, although once the trucks running it should be seeing a solid 14v from the alternator, even if the battery was a bit flat before you started (have you checked the alternator output isnt floating around?)

It might be worth sticking an oscilloscope on the Front right and left sensor feeds right at the ABS ECU and watch the signals for anomalies. If the signals are perfect and the ECU's still flagging a wheel sensor fault, then it has to be an ECU issue.

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Hi elbekko,

I put a multimeter across from the battery neg terminal to the bolts / black cable / brown cables going into the ABS ECU, I had the meter set on audio continuity.. It beeped continually.

As for a reading I could do with some advice as to what it should be and where exactly to measure it at...

Thanks,

db.

As others have said, voltage or actual resistance. You should aim for < 2 Ohm, < 1 preferably.

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  • 3 weeks later...

Hi Guys,

A happy New Year to you all.

I took Aragorn advice and bought myself an oscilloscope, a PC based cheap £48.00 .. (SainSmart DDS 120 from Amazon), works a treat..

I lifted the Landie up onto axle stands, and checked the signals from all 4x abs sensors.

Front right had measured ok resistance wise, had shown ac voltage on my local Landie garages code reader.. BUT...!! when I read the sine AC wave it was intermittent just came along in blocks...

A big thank you to all who gave their advice, off to donate to the forum now...

Cheers,

db..

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