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ABS codes read - both front sensor circuit codes

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Read the codes on my 98 Legacy GT sedan since the ABS light was on and it acts funny.

 

Code 22 and 24 came up - Front right and front left ABS sensor circuit codes .

 

The car did set for awhile. Any tips, i'm wondering if this isn't really sensor related but dirty something?

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[...]Code 22 and 24 came up - Front right and front left ABS sensor circuit codes .

 

The car did set for awhile. Any tips, i'm wondering if this isn't really sensor related but dirty something?

Those codes are for abnormal sensor signal, as opposed to 21 and 23, which would indicate that the ABS ECU saw an open circuit or high input voltage (more likely in the case of poor electrical connections). Nevertheless, you could check sensor resistance, which should be around 1k ohm (+- 20%), and for corrosion.

 

I'd look at the sensor tips, making sure nothing is contaminating them and they're not damaged, that the gap from tip to tone wheel teeth is correct (info for '99 fronts says 0.9-1.4 mm or 0.035-0.055 in, should be same or similar for '98) and doesn't vary much as the wheel is rotated, and that no tone wheel teeth are damaged.

 

If you have an oscilloscope, you can check the output voltage while spinning each wheel.

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the rotors are rusted a good deal from sitting, maybe the ton ring/sensor are contaminated from sitting as well? i'll remove the sensor and have a look at that.

 

how do i look at the tone wheel? i've never looked at one or seen one...and knew what it was anyway! i get the general idea, just never poked around at one before.

 

thanks OBW!

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the rotors are rusted a good deal from sitting, maybe the ton ring/sensor are contaminated from sitting as well? i'll remove the sensor and have a look at that.
Unless the rust on the sensor mounting bolt and steering knuckle is minimal, I'd hold off on pulling the sensor until you check other things first. That bolt has been known to rust/seize/break, and dealing with that is the pain you'd expect it to be. (You can turn the steering wheel enough to get a straight-in run to drill one out, but who needs that? :dead: )

 

how do i look at the tone wheel? i've never looked at one or seen one...and knew what it was anyway! i get the general idea, just never poked around at one before.
If you've ever changed a front axle on one with ABS, you've seen the tone wheel, just probably didn't have to pay attention to it before. :) The brake shield does a good job of hiding the ring when things aren't disassembled, so you have to look in from the bottom (with the wheel off, naturally) to check for contamination and to verify proper clearance. What I've done is measure the gap (just making sure it's within tolerance) at one tooth, then remove the feeler and have someone else turn the hub while I visually check that the gap doesn't seem to change with rotation; also verify that there's no significant axle end play, which could cause the gap to change as the car is driven.

 

Don't forget to check the resistance; breaks in the wire insulation from use/abuse/animals can allow water to flow inside it and get into the sensor itself, corroding the coil. That would usually cause codes 21 and/or 23, but not always.

 

thanks OBW!
You're welcome, I hope this helps.

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Gary, one more thing -- since the car sat around, is the battery at full charge? Sometimes a low battery will cause ABS problems or false codes to be generated.

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good point, i saw that mentioned before, but the battery is fine i think. starts, runs and drives fine without any problems.

 

but i'm glad you brought it up...would the light go away once the issue was resolved? the ABS has been on quite awhile...when i had the battery out, disconnected, charging, etc. i haven't cleared the codes yet. will do that today and see if they come back.

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good point, i saw that mentioned before, but the battery is fine i think. starts, runs and drives fine without any problems.
Then it's likely okay, but I'd throw a voltmeter on, just to be sure.

 

 

but i'm glad you brought it up...would the light go away once the issue was resolved? the ABS has been on quite awhile...when i had the battery out, disconnected, charging, etc. i haven't cleared the codes yet. will do that today and see if they come back.
I don't remember how many cycles without a detected problem it takes for the light to be turned off, so clearing the ABS memory is probably a good idea.

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