I've read quite a few of the ABS threads and haven't seen this problem described elsewhere. My ABS light came on. Took it to my mechanic who has been pretty good over the years. He found a 035 code which implicates the signal from the left front sensor OR the right rear sensor. He hooked up a scope to the input to the control module from those sensors and showed me a picture of what he saw. Interspersed in the regular fluctuating signals there were brief segments where the signal looked like it flatlined (? shorted to ground?). These periods had a consistent duration and occurred with a consistent frequency which was different from the frequency of the normal sensor signal. Thoughts on what might cause this? Or ideas about diagnosing it? Thanks.
Unusual ABS issue (2 Viewers)
- Thread starter tbo_cruiser
- Start date
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NeverFinis
SILVER Star
Just guessing...
1) Excessive metal particles on the ABS sensors.
2) Bad ABS sensor.
3) Broken ABS wiring. Check for damaged wiring.
4) Excessive movement of a birfield. Check all bearings.
5) Excessive movement of rear hub. Check all bearings.
Curious if the signal drop is timed with wheel rotation.
1) Excessive metal particles on the ABS sensors.
2) Bad ABS sensor.
3) Broken ABS wiring. Check for damaged wiring.
4) Excessive movement of a birfield. Check all bearings.
5) Excessive movement of rear hub. Check all bearings.
Curious if the signal drop is timed with wheel rotation.
- Thread starter
- #4
I'll ask my mechanic if he still has the images. He showed them to me, but I don't have copies. I assume he put the vehicle up on a lift with the scope connected rather than doing a road test, but I'm not positive.
smritte
SILVER Star
So....what did he say was the fault?
I'm impressed he used a scope. Most of my diag on these sensors was just a volt meter. Your sensor is just a toothed magnet and a coil. As the tooth passes the coil it produces an AC voltage (just like an alternator). The faster you spin the wheel, the higher the voltage. The voltage will appear as a sine wave. The closer the coil is to the tooth, the higher the power, farther, less.
The fact that you saw a signal at all, says that its "somewhat" working. The signal dropping off will be everything @NeverFinis stated plus a broken tooth on the reluctor wheel.
Nothing against your tech but, this is a very simple diag. You test close to the sensor first. If you see an issue, the problem is there. Having the signal drop is actually not common, they normally just stop working. If its a bearing issue, the wheel wont stay aligned with the sensor causing the signal to get weak as it moves farther away. Once you test, now you check bearings, reductor wheel teeth.........
As for having a pattern he can print out, its just going to be a sine wave with a flatline every now and then. Erratic signals still point to the sensor/reluctor area
Be happy you have an older system. The newer ones require a scope and a better understanding to test.
I'm impressed he used a scope. Most of my diag on these sensors was just a volt meter. Your sensor is just a toothed magnet and a coil. As the tooth passes the coil it produces an AC voltage (just like an alternator). The faster you spin the wheel, the higher the voltage. The voltage will appear as a sine wave. The closer the coil is to the tooth, the higher the power, farther, less.
The fact that you saw a signal at all, says that its "somewhat" working. The signal dropping off will be everything @NeverFinis stated plus a broken tooth on the reluctor wheel.
Nothing against your tech but, this is a very simple diag. You test close to the sensor first. If you see an issue, the problem is there. Having the signal drop is actually not common, they normally just stop working. If its a bearing issue, the wheel wont stay aligned with the sensor causing the signal to get weak as it moves farther away. Once you test, now you check bearings, reductor wheel teeth.........
As for having a pattern he can print out, its just going to be a sine wave with a flatline every now and then. Erratic signals still point to the sensor/reluctor area
Be happy you have an older system. The newer ones require a scope and a better understanding to test.
Last edited:
alia176
SILVER Star
The ABS sensor is just a smooth magnet. The toothed part is the ABS sensor ring back of the birfield. Here's mine cut in half 
All kinds of metal particles will stick to this magnet and cause ABS activation w/o warning.
All kinds of metal particles will stick to this magnet and cause ABS activation w/o warning.
