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Diagnose ABS light?


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14 replies to this topic

#1 BSOD2600

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Posted 31 January 2008 - 07:48 PM

First off, search seems broken since it can't find anything with "abs".

On my 94 TW, the ABS light on the dash has come on several times in the past few days. We've gotten a lot of snow here, so I REALLY want my ABS functional. Turning the car off and on again, clears the ABS memory and often it'll work fine again -- for a while. My tires are within ~2 lbs of each other, even though they look low due to the cold. This is the first time I've had issues with the ABS, so I'm fairly sure it's some how related to all the snow.

I know the ABS module is under the passenger seat and how to read the LED codes. The problem is, I just can't see the LED on mine at all when looking in the carpet hole.
Posted Image

Mine is part number 26720AA210, which doesn't even show up in the stock 90-94 part catalog. Anyone know exactly what year/model it's from?

Anyways, where EXACTLY is the LED on the ABS module, relative to its part number sticker?

#2 nipper

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Posted 31 January 2008 - 08:51 PM

As long as the ABS light is off its functioning.

ABS wont search, but try Anti-lock Brakes. Search wont do three letters, and i dont know if it will do a wild card (*).

(damnit it posted before i was done).

You probabaly have a wheel speed sensor either getting fouled by snow and ice, or you have a sensor starting to go bad. They should be perfect cylinders at the tip. Once they start to erode, they dont work anymore.

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#3 BSOD2600

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Posted 31 January 2008 - 09:10 PM

I realize if the abs light isn't on, it's functional. Problem is that with all this snow, the light some time DOES turn on and thusly no more ABS. I want ABS on snow.

After more research, I believe I've got the newer ABS-2E system. That means there is no LED on my ABS unit. Instead, I have to enter abs diagnostic mode by grounding a wire to the "L terminal" of some connector... and then my ABS light should flash. Supposedly it has long term memory too and will keep 3 codes (where as the rest of the early legacy models don't keep any at all).

Well I found a 2-pin connector near my fuses:
Posted Image

I tried grounding each one to the body while having the ignition on / run. Neither resulted in any flashing codes. So not entirely sure if I've got the correct connector or if I'm doing something else wrong.

#4 nipper

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Posted 31 January 2008 - 09:18 PM

http://www.ultimates...antilock brakes

Antilock Brakes works on the search.


nipper

#5 porcupine73

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Posted 01 February 2008 - 10:43 AM

I think you need to ground terminal L with the key off. Then after grounding L, you go to key on, then it flashes out the codes.

Posted Image

#6 BSOD2600

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Posted 01 February 2008 - 02:03 PM

thanks! I got it! It WAS that abs check connector in the kick panel. Forget if I had originally only turned the ignition to ACC instead of ON.

Anyways the three codes it threw were: 24 - Left Front Sensor (Short), 26 - Right Rear Sensor (Short), 29 - Tone Wheel. I'll clear them out and see what comes back.

#7 ericem

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Posted 01 February 2008 - 02:07 PM

Last time I inspected behind the discs I found the abs sensor and the disc it read when driving to get a signal gets pretty rust. This might be exactly what is happening. Mine I just sanded a bit and that's it.

#8 porcupine73

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Posted 01 February 2008 - 03:45 PM

Mine is part number 26720AA210, which doesn't even show up in the stock 90-94 part catalog. Anyone know exactly what year/model it's from?


That shows up as:
26720AA210 Brakes - Anti-lock brakes - Control module
impreza, 4wd, auto trans 1993 - 1994
impreza, 2wd 1996
impreza, 4wd, auto trans 1995 - 1996
legacy, w/o tcs, 2wd 1995 - 1996
legacy, w/o tcs, 4wd, auto trans 1995 - 1996

#9 Skip

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Posted 01 February 2008 - 04:17 PM

I have a code also
Please if I may ask

First is it the white connector
with the green and red
wires to it?

If so which is terminal "L"
the green or the red wire
in the terminal?

Posted Image

#10 BSOD2600

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Posted 01 February 2008 - 05:09 PM

ericem: I took the car to les schwab and had them look over stuff briefly. The tech in the Alignment center it all looks fine. I'll consider playing around with it more when there isn't any snow on the ground.

porcupine73: Interesting, since mine is a 94 AWD TW (which of course was originally 4EAT before I switched to 5MT).

Skip: It's the red wire. Either I didn't make a good ground connection or something. But it only would enter diagnostic mode every other time I turned the key to ON.

Between Les Schwab and another subaru shop I called (Smart-Service), they both think everything is probably alright and it's just the computer freaking out. The excessive slipping in the front/rear throws it off.

#11 Skip

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Posted 01 February 2008 - 05:25 PM

Thanks BSOD, well done on the picture.
I have the same ABS pooter
in my 94 GT wagon.
Posted Image
She has the raised roof but I have been
kindly told the "touring wagon'
was reserved for the turbo wagon.
(I have two of those they don't have the
"touring roof"??)


Gonna have a look tomorrow.

#12 OB99W

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Posted 01 February 2008 - 07:18 PM

[...]Anyways the three codes it threw were: 24 - Left Front Sensor (Short), 26 - Right Rear Sensor (Short), 29 - Tone Wheel. I'll clear them out and see what comes back.

It may take a while after clearing before all those codes reappear, even if they're all still a problem. When the ECU goes into fail-safe (due to an active fault), it no longer senses or stores codes for additional faults. That means for more fault codes to be stored, the first fault has to be intermittent.

The next time the ECU is active (no fault is occuring), it can sense additional faults. If a fault then occurs, but it's the same as before, the ECU will fail-safe and there will still be only one fault code in memory. If a different fault appears before the original one, its code will be stored in the second memory position, and the ECU will again go to fail-safe mode and sense no other faults.

A similar sequence of events has to happen for a third code to be stored. That means the first two faults have to be intermittent, not presently occuring, and the "new" fault has to occur before either of the previous ones.

Since you read three codes (the max that the ABS-2E ECU can store), for the reasons just explained it could take some time before all of them might be stored again. If the cause of any of the codes is repaired, it's then likely that any remaining problem will next store its code more rapidly.

Therefore, to expedite the repair it's probably best to read the memory as soon after the ABS light comes on as practical, and deal with the cause of the particular code. Then, clear the memory and see what comes back.

Something to keep in mind is that the sensor has to "see" all the teeth on the tone wheel. Anything that weakens or disrupts the signal can cause a fault to be sensed. That includes snow packed in the ring or corrosion damage to the sensor tip. I've found that if the sensors and rings are in good shape, the system is pretty tolerant of weather-related conditions, but marginal sensors allow fault codes to be easily generated.

Because the environment the wheel sensors are in is pretty harsh, besides corrosion of the sensor tips, another common problem is that the sensor cable is prone to cracked insulation. Once that happens, water (and salt) can get in and damage the wire itself. If you find cracked insulation, the sensor may be unable to provide a proper signal.

I don't know off-hand what operational differences there are between the auto and manual versions of the ABS ECU, but I wonder if the fact that you changed the trans has anything to do with the problems. When did they start occuring relative to when the trans swap was done?

Sorry for the length -- I hope the above helps.

#13 BSOD2600

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Posted 01 February 2008 - 09:20 PM

When did they start occuring relative to when the trans swap was done?

I've owned the car for a year now after the 5MT swap. The past week is the first time I've EVER had the ABS light come on. I've had the ABS system engage many times, both on dry/wet/snow under heavy braking; so I'm fairly sure it's just fine.

Now I know how to read the ABS codes, I'll be doing that each time the abs light turns on. Once there isn't any snow on the ground, I'll more closely check the ABS sensors on each wheel, check for rust, etc.

#14 1-3-2-4

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Posted 24 August 2010 - 11:14 PM

So that's the ABS connector to get the codes from? man all the other FSM said a black plug near and under the steering column and I was trying to tell people I don't see anything like that.

Going to have to check after work.

#15 porcupine73

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Posted 25 August 2010 - 07:24 AM

It depends what ABS setup you have. There's a really good article about Subaru ABS on Endwrench that has pictures of each system and tells for each system how to get the codes.




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