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'89 740 Turbo Wagon anti-lock light[ALL/1998] posted by Jim Ray on
Wednesday, 22 October 1997, at 8:58 p.m.
Light on dash comes on - no flicker - just comes on and then stayes on. Only happens once in a while. Light stays on 'till I shut the car off.
I also notice that the anti-lock system seems to "chatter" some during brakeing while turning, when this is noticable the light on the dash comes on a little more frequently/
I noticed that when the light comes on it typically happens soon after I start driving, say the first couple of minutes. If it stays off for the first 15 minutes of driving, it has never come on after that during that "trip".
Dealership thinks the sensors are getting brake dust on them that clog up the sensor. Dealer pulls the sensor and blows out the dust and cleans up the sensor frequently (only looks at the sensors on the front wheels). Dealer does this every couple of months or during any service - he does this free - good dealer - wants to sell me a newer Volvo.
Cleaning does seem to reduce the frequency of the problem - but - it still happens.
Anybody got any ideas on what else to look for?
Re: '89 740 Turbo Wagon anti-lock light[ALL/1998] posted by Dave Stevens on
Thursday, 23 October 1997, at 4:46 p.m.
Re. ABS chatter during braking/turning:
If this happens at low speeds only and on "slick" pavement then that's fairly common and of no particular concern, system is a little too sensitive under those conditions. Had this problem on my '89 740, Volvo said there was an improved sensor available and replaced mine under warranty -end of chatter. I don't see a TSB on this though. Maybe one of our mechanics knows more on this.
Re. ABS light coming on and staying on:
Based on my trusty AllData ABS troubleshooting guide (Volvo TSB), before you go assuming the ABS unit is faulty, check the following:
a) Check ABS unit ground connections (clean this connection)
b) Check ABS unit and sending unit wiring and connectors
c) Check ABS front sending unit connectors under tower struts ('88 problem)
d) Possible air in brake lines (after bad bleed or low reservoir)
e) Check/clean ABS pulse wheels and sensors, make sure nothing damaged or loose
f) Check that speedometer is working normally ('87-'88 problem)
g) Check that sensor wiring is away from high voltage stuff (distributor/coil)
Otherwise you're probably looking at a faulty sender or, worse still, ABS unit.
I clean my ABS sending units as part of my annual brake pad check (and snow tire removal).
NB. Pulse wheels changed from 96 tooth to 48 tooth starting in '89 740
Re: '89 740 Turbo Wagon anti-lock light[ALL/1998] posted by Mark Klein on
Thursday, 23 October 1997, at 9:56 p.m.
Could be a flaky sensor or even a damaged tooth on a front hub. The rear sensor/trigger wheel is in the differential cover and won't accumulate dust with time. Very rare for anything to happen to this sensor.
The "updated sensor" is sort of a "retro-fit" for this type of problem. It wasn't a recall. The old style sensor has a rectangle shaped magnet and the new one has a diamond shaped tip. I wouldn't expect the old style sensors to work too well.
Pull the sensors and spin the wheel to inspect the trigger wheel. You can look through the sensor hole if you watch closely.