At 08:50 AM 7/13/02, Dag-Erik Tønne wrote:
>My 86S2(Euro) is beginning to get some electrical gremlins I dislike.
>Sometimes the ABS warning light is on, sometimes it's not. My guess is
it's a bad earth connection . Where do I begin the search ?
Under the car. Check and clean the connectors at each wheel. These are
normally 25 x 35 mm cylinders that have a snap-on jacket. Also check the
teeth on the hubs to ensure that they are not choked with deposits.
Wally Plumley
928 Specialists
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car is now sold but of course would have been difficult to sell with the warning lights all coming on above 5 mph.
Symptom was just as such, above 5 mph the central warning light would come on and could be re-set; however the antilock light would remain on in the instruments. I raised the rear of the car, and put the car in gear. Ran it to about 40mph and the warning light did not come on. Even when I disconnected one of the sensors and did a check on the outputs, the warning light did NOT come on... FYI, the output of the sensor shows a +2 to -2 Volt oscillation.
I then put the front op in the air, and my left front driver's side sensor output stayed firmly at 0 Volt... Replaced the sensor (thanks Mark at 928 International) for a much more reasonable price than dealer cost, and now the warning lights do not come on anymore.
Thanks to all who offered advice and help.
Jan
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Past week I've been greeted by the orange 'Anti-Lock' warning when I drive
home from work. Car gets to sleep in warm garage at night so the warning is only
triggered during the cold storage in the daytime.
I've been advised 2 years ago I had a cracked front sensor. Figured water got in
and was freezing and disabling sensor at work.
Then going for fuel yesterday, gas station was busy so I figured I'd better
reset tire pressures.
Go my handy digital pressure gauge out and found 3 of the tires had fallen to
the mid 20's.
I will be saying many a 'Hail Bwaaah' in the temple of 928 for such
transgression.
Most of the time I set for around 32lbs of air and never like to stray below
28lbs.
Granted it was a balmy 16deg F but that's no excuse for not resetting tire
pressure for the cold.
Warning light went quiet on ride home.
Eureka!
ABS had been working as designed and the 3 limp tires had caused a rolling
diameter difference high enough to trigger the warning.
EW
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The ABS ecu has two self-test cycles. One is when you turn on ignition and the second is when driving about 6km/h. The first checks if all systems are go (power, relay, gnd, wires), and the second monitors the presence of the wheel sensor signals. So if the ABS light does not go out when turning the ignition on, the ecu itself is suspect.
The ABS light will be on (same as PSD if you have this) when turning on the ignition. It will go out when the engine is started.
However there is one thing that is uncertain to me. A sensor that is crushed by oxidation may have a short circuit to chassis ground. That could be picked up by the ECU as a failure instead of a sensor problem. If the car has a RDK and you own our diagnostic UDT or PDT system, you can real time monitor what is happening at the sensors. The RDK shows the actual values in real time.
Intermittent ABS errors are often caused by a failing ABS relay. A special relay with a overvoltage protection inside. The relay contacts sometimes loose contact and the 12v power drops, causing the ecu to alert for a failure.
Theo
1992 928GTS midnight Blue
The Netherlands