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ABS problems on 90 vette

malc350

Well-known member
Joined
Jul 6, 2002
Messages
337
Location
Essex, UK
Corvette
1996 LT-4 Z51 CE
A while ago I posted a problem with my ABS. When I do the ALDL check on the codes I get a code 31 (right rear sensor fault) and a code 25 (left front sensor fault). The codes appear in that order: 31 first, then 25, is that right?

I checked the reistance of both these sensors. The right rear was slightly out of range (high resistance) so I replaced it but I still get the same codes as well as the service ABS light in the DIC.

I have tested the resistance at the white connector near the ABS modulator and that is near as dammit the same as the resistance at each sensor. I have concluded from this that there is no short in the wires from the sensor to the modulator. Again is that the right conclusion? I'm a bit of a rookie with electrical faults but I'm trying to act logically!

I find it hard to believe that both sensors could fail at the same time (!!!) and the fact that I have replaced the right rear sensor and still have that code (RR fault code 31) makes me think that the fault lies elsewhere. I suspect an earth or some connection somewhere (I'm guessing).

Can anyone suggest a likely cause of both fault codes appearing at the same time? It's not as if they are even close to each other on the connectors. Does anyone know if there is a connector under the dash anywhere? Maybe leading to the DIC or brake pedal. The reason I ask this is that the wiring seems OK from the sensors to the modulator but when I trace some of the wires they disappear under the carpet and run under the sill cover towards the front of the car. I figure there must be a connection somewhere to check?

The only other thing I can think of is that the ABS ECM is detecting faults that aren't there and that the ECM is at fault. Sound expensive.

Thanks for your help in advance.
 

Rabbit

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Joined
Dec 19, 2001
Messages
956
Location
sonoma ca usa
Corvette
2004 C5 coupe, MSGM & 2014 Cad SRX Crystal red
Have you cleared the DTC"S from the CCM.? :dance
 

malc350

Well-known member
Joined
Jul 6, 2002
Messages
337
Location
Essex, UK
Corvette
1996 LT-4 Z51 CE
ABS problems

I have disconnected the battery for a while but the codes come back. Is there a better way to clear the codes?

I thought (don't know if I'm right here?) that the system self-diagnoses every time the car is started so the light will only come on if the fault is still present?

When I start the car the "service ABS" light does not show until I have driven a few feet. I hear the ABS motor running for a while before the warning comes up.

Also when I start the car the "ABS Active" light doesn't light up (the bulb is OK, I checked). I didn't know if this should show to check that it is working on startup.

Thanks for any help you can give me.
 

vigman

Motor head!!!!
Joined
Feb 13, 2001
Messages
3,471
Location
Valencia, CA,USA
Corvette
88 Convert ( SOLD ) /1973 coupe 4 speed/1964 Vert!
Things I know

The ABS active light will not come on till the ABS is engaged.

And since your ABS is NOT working... you will never see that light!

But IF it were working... when your in a situation that that light comes on...I do not think you will be looking at the DIC panel!


Vig!
 

vigman

Motor head!!!!
Joined
Feb 13, 2001
Messages
3,471
Location
Valencia, CA,USA
Corvette
88 Convert ( SOLD ) /1973 coupe 4 speed/1964 Vert!
Wheel sensors

The wheel sensors are like your ignition pickup.... you have a GEAR like rotor moving by a pickup coil.... each time the HI point flys by a pulse is genetated... this pulse has to be recieved by the ABS module from 4 points in your car ( each wheel )

C-242 is a 10 way connector in the left hand side cargo compartment. All the ABS sensors are on that connector.

Something to check for..... if stray metal builds up on the sensor pole pieces..it will attenuate the pulses. Make sure they are CLEAN.. and the spacing is correct between the gear & the pickup.


Look @ the Mid America catalog..to see what a front wheel bearing looks like and you will see "the gear".

How are you getting your error code for the ABS?


Vig!
 

Rabbit

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Messages
956
Location
sonoma ca usa
Corvette
2004 C5 coupe, MSGM & 2014 Cad SRX Crystal red
This info is for a 95. Don't know if it relates, but the manual states that the
codes cannot be cleared by disconnecting the battery. You will have to get into the diagnostic mode of 9.7 ABS/TCS. Clear ABS/TCS codes.

I also donnot know which pins you have to ground in a 12 pin DLC. Apparently you got the codes so you know.

I'll give you the procedure for 95 which is as follows:

With ignition "off" ground terminal ?

Turn ignition "on"

Press the " trip reset" button on the DIC
until the desired system is displayed in the trip monitor of the cluster. (9)

Press the "trip/odo" button on the DIC
until the desired diagnostic mode is displayed on the trip monitor area of the cluster. (9.7)

Press & hold the "eng/met" button on the DIC until "-----" is displayed in the speedometer area of the cluster

Turn ignition "off".

Turn ignition "on" to verify that DTC"S are cleared.

I had a 90 prior to my 95 & I believe the CCM"S are very similiar, at least I hope so.


Hope this is of some help.
.:w
 

malc350

Well-known member
Joined
Jul 6, 2002
Messages
337
Location
Essex, UK
Corvette
1996 LT-4 Z51 CE
ABS codes

The thing that really mystifies me is that i'm getting 2 codes at the same time: right rear and left front. One night the warning light displayed on the DIC and it's been there ever since. I just can't believe that 2 sensors could develop a fault at the same time!

I got the codes by shorting the respective pins on the ALDL. Rabbit, your procedure is right for a 95 (I have the manual for my old 93 as well) but the 90 doesn't display the 9.0 codes - that came later on - 92 or 93 I think.

The sensors are absolutely clean, they look like new after I've cleaned them and the teeth on the wheel bearings look OK from what I can see.
 

Rabbit

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Messages
956
Location
sonoma ca usa
Corvette
2004 C5 coupe, MSGM & 2014 Cad SRX Crystal red
Perhaps someone with a helms manual for 90 can assist you?

Anyone?:)
 

Rabbit

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Dec 19, 2001
Messages
956
Location
sonoma ca usa
Corvette
2004 C5 coupe, MSGM & 2014 Cad SRX Crystal red
Malc350, Whats the status re;ur ABS problem. I have alittle more info I can e-mail.
 

malc350

Well-known member
Joined
Jul 6, 2002
Messages
337
Location
Essex, UK
Corvette
1996 LT-4 Z51 CE
ABS problem

Thanks Rabbit, I still have the warning light. Sometimes when I access the fault codes I get different codes! So far I have seen:

Code 31 (right rear sensor)
Code 25 (left front sensor)
Code 61 (relay)
Code 63 (relay)
Code 71 (EBCM error)

The code 61 and 63 have disappeared but the 31 and 25 are always present. The 71 has only appeared today. I have a felling that this is the one that tells the true story - that my brake ECM (EBCM) is shot!

If you have any info please let me know. I'm also going to post a question on the forum.

The good news is I found my AC electrical problem. It was a short under the hood.
 

Rabbit

Well-known member
Joined
Dec 19, 2001
Messages
956
Location
sonoma ca usa
Corvette
2004 C5 coupe, MSGM & 2014 Cad SRX Crystal red
Heres alittle info on a 91 which is the closest I could get to yours.....

) Diagnostic Request Line Procedure[/b]

a. Turn ingnition off
b. attach a jumper to the ALDL connector terminal "H"
c. Attach a jumper to the ALDL connectot terminal "A"
d. connect the jumpers to each other
e. turn ignition to "RUN" (this will enable flash code diagnostics)
f. Disconnect jumpers for appx 1 second then reconnect jumpers for no less that 1 second. Repeat this action 4 times within 10 seconds, leaving jumpers connected upon completion of the 4th interval.

Observe the "SERVICE ABS" light. Only Code 12 should be flashed. If not, trouble codes have not been properly cleared. Begin clearing procedures again beginning with step (a). If codes are cleared, wait at least 15 seconds before turning ignition "off".

3)Ignition Cycle Default
If the ignition is cycled 100 times without a particular fault reappearing, that fault code will be erased from EBCM memory, and the ignition cycyle counter inside the EBCM will be reset to zero.
 

Edmond

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Joined
Aug 1, 2001
Messages
5,218
Location
Louisiana
Corvette
2003 Z06
Guys,

This is kind of a dumb question, but I have to ask anyways:

Do I have ABS on my 88'???

I've never had the ABS kick on during hard breaking, even in slippery conditions, so I'm assuming that I do not have ABS.

Someone please let me know!
 

vigman

Motor head!!!!
Joined
Feb 13, 2001
Messages
3,471
Location
Valencia, CA,USA
Corvette
88 Convert ( SOLD ) /1973 coupe 4 speed/1964 Vert!
Edmond

YES YOU DO!

when you first start the car.. and back up... do you hear a little growl in the cabin?

86 was the first year of ABS


Vig!
 

vigman

Motor head!!!!
Joined
Feb 13, 2001
Messages
3,471
Location
Valencia, CA,USA
Corvette
88 Convert ( SOLD ) /1973 coupe 4 speed/1964 Vert!
Malc....

Where was the short located for your A/C?


Vig!
 

malc350

Well-known member
Joined
Jul 6, 2002
Messages
337
Location
Essex, UK
Corvette
1996 LT-4 Z51 CE
ABS Codes

When I start the car I do hear the ABS motor running, and after it has finished its self-check the light comes on and the motor stops.
 

vigman

Motor head!!!!
Joined
Feb 13, 2001
Messages
3,471
Location
Valencia, CA,USA
Corvette
88 Convert ( SOLD ) /1973 coupe 4 speed/1964 Vert!
Sorry Malc...

That was ment for Edmond ( the brake growl)



Vig!
 

malc350

Well-known member
Joined
Jul 6, 2002
Messages
337
Location
Essex, UK
Corvette
1996 LT-4 Z51 CE
ABS

My fault I realised after I sent the message!

Malc.
 

vigman

Motor head!!!!
Joined
Feb 13, 2001
Messages
3,471
Location
Valencia, CA,USA
Corvette
88 Convert ( SOLD ) /1973 coupe 4 speed/1964 Vert!
LOL

It must be the time lag across the pond!


Vig!
 

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