ABS unit humming after engine turned off

[spideyz]

So the ABS light comes on while my wife is driving around town yesterday. When she gets home, I look at it and I pop the hood with the engine off. The ABS unit is humming like the pump motor is running. Pulled the neg. terminal on the battery and of course it stops. Put the neg terminal back on, humming starts up. Read the ABS trouble code under passenger seat and found number 9 which is: "Faulty motor and/or motor relay or broken or shorted harness circuit." I took off the relay cover on the unit and pulled the relay. Humming continued. Put relay back in... humming continued. Then I pulled the ABS fuse from the main fuse box and the humming stopped. So now I have disabled the ABS system. What is the best way to troubleshoot this problem. My first inclination is to replace the relay in the ABS unit and see, but I hate wasting money if that turns out to be something else. Any advice is appreciated. Thanks. Keith

[WoodsWagon]

The motor is good if it's humming, the relay isn't the problem because removing it doesn't stop the problem. Is the motor switched to ground by the relay or switched to power? If it's switched to ground, you have a short between the relay and the motor.

[spideyz]

It looks like from the diagram that the relay switches the motor to power. Or please correct me if I am wrong. See the attached .gif (hopefully it is viewable, if not check out the center diagram here:

http://www.autozone.com/servlet/UiBroker?ForwardPage=/az/cds/en_us/0900823d/80/1e/76/7a/0900823d801e767a.jsp

 

How can the motor still run if the relay is pulled? What type of short or other fault could cause this?

 

Thanks for the help! Keith

[WoodsWagon]

I can't read the diagram, too small.

Have you taken apart any connectors and reconnected them lately? Or had any work that could involve that done? Sometimes a pin can fold over in the connector and short to power. The motor is getting it's power through the ABS fuse, so you know that it's a problem in only the ABS harnesses.

[WoodsWagon]

The wire between the splice and pin 14 on the ABS computer could have picked up 12V somewhere.

 

It's a switch to load circuit, so it's a positive side short somewhere.

[avk]

There's a TSB for sticking ABS pump motor relay, it could be that.

[spideyz]

Thanks for the replies. If you click the diagram on the Autozone page it will open in a larger view so it should be readable. I'll try searching for the TSB. I haven't had any work done on the car at all recently (except topping off the oil). Any tips on trying to locate a short in the power?

 

Thanks again. Keith

[spideyz]

After looking at an exploded diagram of the ABS unit it looks like the relay I pulled out was probably the Valve Relay and not the motor relay. The one I pulled was in the rear position under the relay cover. See the attached diagram. There was a relay-like box in the forward position, but it didn't look like an actual relay. It looked more like a hunk of plastic with a raised "+" mark protruding on its top--like a filler or something. Hard to discribe. I think I'll take another look at it later tonight and see if it is, in fact, the motor relay. Thanks for the help.

 

Keith

[spideyz]

Update:

 

Put the fuse back in last night and no more humming. Pulled the ABS relay cover off and found the right relay to pull this time. Anyway, looks like an intermittent problem. When it happens again, I'll pull the relay to confirm the "sticky relay" theory, then replace the relay. Thanks guys for all your input. Keith

[Virrdog]

Random power issues scare me. I still don't know why my amps will spark across a screwdriver with the battery disconnected...

[uniberp]

Your 'amps' have capacitors to handle spiky power needs. They need time to discharge. See the 'amp' spec or manual.

 

Random power issues scare me. I still don't know why my amps will spark across a screwdriver with the battery disconnected...