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Dr.Automotive
Dr.Automotive, Auto Mechanic
Category: Toyota
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Experience:  Automotive Degree Shop Experience
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2000 toyota avalon: diagnostic code..right rear brake sensor, no

Resolved Question:

I am getting the abs light "on" with my 2000 toyota avalon. After checking the diagnostic code using the blinking ABS light sequence...my error is an open ciruit for right rear brake sensor, no. 38. No other codes are blinking. I checked the resistance of the sensor and get 1.64 k-ohms. no shorts to ground. I have 8.8 v at the sensor connector to when acc switch is in on position. I get 10.44 v when engine is running. Are these normal readings. I read that greater than 5v readings are too high for the sensor circuit. Is this true?
Submitted: 2 years ago.
Category: Toyota
Expert:  Dan replied 2 years ago.
Welcome to JustAnswer, my name is XXXXX XXXXX I'm here to help get your problem resolved. Ask follow up questions, thanks. Visually inspect the Right Rear Wheel Speed Sensor for any harness damage and inspect the tone wheel for debris or damage. Ohm the Right Rear Wheel Speed Sensor - specification is 1.2 - 2.3 k ohms. Scope the Right Rear Wheel Speed Sensor on the Green wire while driving and look for a good consistent sine wave signal of about 4 volts peak to peak at about 20 MPH. Also compare the signal to the Left Rear Wheel Speed Sensor as necessary. Verify that the Right Rear Wheel Speed Sensor wiring is not open circuit or shorted to ground. Remove the rear seat cushion and side seat back, to access the Right Rear Wheel Speed Sensor connector.
Customer: replied 2 years ago.
Ok , you did not answer my question about the voltage readings I took at the connector therefore I must assume that this was an automated reply. I already stated that I checked the resistance and the potential for short circuits. I do not have an oscillascope to run the test and how do you look for the graph while driving?
Expert:  Dan replied 2 years ago.
There are no resistance specs...You can just lift wheel and use a voltmeter to check AC votlage output of sensor while spinning wheel and compare it to other side. Let me know if you have questions, thanks.
Customer: replied 2 years ago.
Relist: Other.
Answer was an automated reply, your expert didn't answer the question I posted.
Expert:  Dan replied 2 years ago.
It wasnt a automated reply...I told you in detail what to do....If there is something I missed or more I can add let me know.
Customer: replied 2 years ago.
You didn't acknowledge my information about the voltage readings i gave you in my original question? Would you like to answer them now.
Expert:  Dan replied 2 years ago.
The voltage reading makes no sense...Unless the abs module failed or wire is shorted....Wires should not have voltage when wheels are not moving.
Customer: replied 2 years ago.
Ok, thats a start. I have checked both the terminals to the plug connector at the sensor and to the lateral wire going to the junction box plug at the lower right front of the car and I have continuity and no shorts to ground or to each other. I am receiving 8.8v when the ignition key is set to accessory on and i am getting 10.44v when the car is running at the plug terminals of the sensor. Can you refer to someone who might have an answer to why this might happen?
Expert:  Dan replied 2 years ago.
I just told you.....wire is shorted or abs module has failed.
Customer: replied 2 years ago.
If ABS module has failed, I would expect to see no voltage. no shorts in wiring.
Expert:  Dan replied 2 years ago.
If wiring is not shorted abs module is only possible option.
Expert:  Dan replied 2 years ago.
Here is the run down on how the wheel speed sensors work...They have two wires that go from the sensor to the abs module...The wheel speed sensor is a hall effect sensor which produces voltage with a magnetic field...As wheel rotation speed increases so does the amount of AC voltage this sensor puts out....ABS module interprets the amount of voltage as a specific voltage....So there there are two wires, a sensor, and a abs module......which would mean the ONLY way voltage could be on wires going ot sensor is if wires shorted or abs module failed....Thats about the best I can explain it...If you would like another opinion let me know.
Customer: replied 2 years ago.
Ok, your stating that the voltage is produced solely by the sensor as it picks up the magnetic field by the spinning wheel therefore there shouldn't be any voltage when the wheel is not spinning. Yet, I've read that there should be 5v or less through the circuit when wheel is idle. Are you telling me that this information is incorrect?
Expert:  Dan replied 2 years ago.
If you have 5v on wire and sensor is what produces the voltage....This means the abs module which the sensor connects to internally failed causing a internal short to voltage inside module...This is really simple but without some basic electrical knowledge its tuff.....I took classes and have years of experience....I couldnt have learned this in a 5 minute convo either.
Customer: replied 2 years ago.

Is the ABS module also known as the ECU?

If the abs module is shorted wouldn't I have seen more than 1 error code show up?

Expert:  Dan replied 2 years ago.
The ECU is "engine control unit" which is for engine control....seperate from the abs module...and without knowing where the abs module is you couldnt have checked wiring for shorts....the abs module is under hood attatched to hydraylic brake control unit.
Customer: replied 2 years ago.
Under the hood is the solenoid relay, the motor relay and the actuator? Which of these is the ABS module? Also, I ask again, if the module is blown wouldn't I get more than one error code?
Expert:  Dan replied 2 years ago.
I'm going to opt out of question, someone will respond automatically. DO not reply or question will be locked to me only. Thanks.
Expert:  Dr.Automotive replied 2 years ago.
Welcome to Justanswer, My name isXXXXX am here to help.

This vehicle has a sensor that should not be giving out voltage while stationary. Most likely it thinks its in motion which would cause voltage when its not moving.

Disconnect the wheel speed sensor then check the connector see if there is voltage going to the sensor. If so then you have a short in the abs module. Verify the other sensors are also having the same problem or atleast one. They should have no voltage according to the information I show and the type of sensor you have Replace the sensor best move especially if you dont have access to a scope. if voltage is gone with sensor unhooked replace the sensor.

Let me know Please press ACCEPT by my name if I have answered your questions. Thanks in advance

Danny
Customer: replied 2 years ago.

Here is the link to the information I stated in my convo with your expert:

 

http://www.ehow.com/how_7591href="http://www.justanswer.com/toyota/5k0g1-toyota-getting-abs-light-on-2000-toyota.html22_test-abs-speed-sensor.html

 

Please read the information and reply to its validity. This states that there is voltage going to the sensor and I never got a response from your tech about this information.

It says that the voltage should be less than 5volts. Your tech dismissed my info that I stated at the top of my convo. I said initially I took voltage readings at the sensor plug or harness connection 2 or 3 times before he finally replies, "The voltage readings make no sense..." He says this after I posed the information 2 or 3 times. Also, I am using terminology used in a Haynes reference manual which uses "ABS ECU" in place of ABS module. I wanted to confirm that term with the tech but he dropped the convo due to frustration. And one more thing, the ABS ECU is adjacent to the glove compartment according to the Haynes reference book and not under the hood near the ABS actuator again a Haynes reference. I may be a DIY'r with limited knowledge but I do reference things before I approach the problem.

 

Expert:  Dr.Automotive replied 2 years ago.
The best thing you can do is take that hanes manual and toss it. Go to www.alldatadiy.com get access to your vehicle. Also when it comes to vehicles do not always trust things you hear. I went through this is depth because there are sensors that can carry voltage this is on newer chryslers and some other vehicles. I have not yet seen a toyota that uses this. Some do however give out a diagnostic ref voltage of 2.5 not this one. So now that we have established there are many different sensors how do we know which one you have? We take a manual from a automotive database and pull up the electrical diagram for the abs circuit which I have you indeed never have voltage unless the wheel is moving. There are also 2 systems one will have the module in the glove box the other will be under the hood here is a image of one under the hood. graphic
Customer: replied 2 years ago.

Great, thanks for the image, it is the only one I have come across that has the actuator in the same spot as my car. most others use a camry image along the front right wheel fender. Bear with me as I feel we are making progress. Please read below.

 

This is a Bosch ABS system. Not Nippondenso.

All the following measuements were taken with sensor harness disconnected and off the feed wire to sensor.

Ok, I have checked the other rear wheel which has not been giving me an open sensor code. With the harness sensor disconnected and no running engine, and no key in ignition I get 290 millivolts. With engine running and harness still disconnected from sensor I get 4.8volts. With key in ignition and accesories on, engine off, I get the same 4.8 volts. This is the sensor that is not giving me an error code. Are you sure no voltage should be present with wheels not rotating? If so, why do I not get a code for this sensor as well as the other? Nor do I get an ABS ECU error code? wouldn't I get an error code for the abs control module if it were blown?

On the side giving me the open sensor error code I get 11.4 volts, not millivolts, with engine off and no key in ignition and sensor disconnected. With engine running I get 13.4volts and with acceroriies on, no engine running, I get 11.6volts.

 

Expert:  Dr.Automotive replied 2 years ago.
There should not be any voltage in this system. So this has to be a failure in the module itself. I would get a used replacement from www.car-parts.com or local salvage yard and replace it should fix the problem. The reason why there are no codes is because the module is bad itself so its questionable.
Dr.Automotive, Auto Mechanic
Category: Toyota
Satisfied Customers: 3803
Experience: Automotive Degree Shop Experience
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Customer: replied 2 years ago.
This is Harry w/ ABS problem. You were helpful and I apologize for frustrating you and Dan with my problem. I did find a short at the module control output plug. It was located on the Bosch actuator. Your information was helpful but partly correct. After carefully cleaning the terminals and replugging up the module (it didn't blow the computer thankfully) I still got 4.8volts at the rear sensor connectors with the connectors unplugged on both rear tires. The ABS light is out for now. I want to give you a bonus as well as Dan from last night. How do I bonus you two as well as apologize for frustrating Dan who was correct with the short fault diagnosis? But you guys do need to research the voltage to sensor thing because your database info isn't complete on that.
Expert:  Dr.Automotive replied 2 years ago.
That is very interesting. I only show two types of systems that show current and yours shouldnt but I will again have to do some more studying. You can send a tip by going to the page at the top my questions then your able to add a tip on the question. I will let dan know as well or you can accept one of his answers but I am a co worker of him so I am sure we can work something out either way. Me and dan went over this very extensively last night and leaves much to be desired on the matter to me based on the limited information. Thanks in advance for accepts and tips they will be put to good use.

have a great one.

Danny
Dr.Automotive, Auto Mechanic
Category: Toyota
Satisfied Customers: 3803
Experience: Automotive Degree Shop Experience
Dr.Automotive and 4 other Toyota Specialists are ready to help you

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