Lost Ground

Brian Owner/Technician Detroit Lakes, Minnesota Posted   Latest  
Question
Braking
2005 Ford Expedition Eddie Bauer 5.4L (5) 4-spd (4R70W)—1FMPU18525LB12972
C1165
Abs Light On

Somehow the ground inside the ABS module is lost for the right rear signal. What would happen if I jumped the ground to the other rear speed sensor ground at the module plug? when i did it for testing the code goes away. Looking for some quick answers here.

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Brian Technician
Bridgewater, New Jersey
Brian Default
 

ABS sensors are generally AC signals. Wo they create their own voltage and report back to the module. I can't recall ever seeing otherwise. If you jump 1 wire it's going to throw off the signal from both sensors. If you wanted to confirm module operation you could eliminate the questionable sensor and jump the other side to the wires. Then the module would see them reading the same speed. If you…

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Brian Owner/Technician
Detroit Lakes, Minnesota
Brian Default
 

this system has a 12volt signal on one side and a ground on the other. both sensors have there 12 volt signal from the abs module but the right rear has no ground connection inside the abs module hence, when I jump the ground over to the left rear's ground, the circuit completes and turns the light off. but is it ok the join these grounds going into the module? isn't a ground just a ground?

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David Owner/Technician
Kitchener, Ontario
David Default
 

No because even the Ford diagnostics describes each ABS sensor as a 7 or 14 mill amp current source depending on weather or not a tooth or an air gap is in front of the sensor. So as per ohms law if you connect two resistances together in parallel you will halve the ohms and double the current flow of the circuit in practical terms you will likely have an effect on the current and on the…

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Agree
David Owner/Technician
Kitchener, Ontario
David Default
   

They are AC signal riding on top of a dc bias or test voltage, one side is high is a voltage and the other side is low. Not an actual ground. Hypothetically it would depend on which side the abs module reads the signal from when it converts it to digital. Therefore jumpering to another sensor does not seem like a good idea because you are combining two circuits together. I would suggest…

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Eric Technician
West Frankfort, Illinois
Eric Default
 

This is where shop owners and technicians make things hard when they are not. You have tested and concluded that the module has an internal circuit issue. The truck needs an ABS module plain and simple if the customer doesnt want to buy one charge for the diagnosis and let it go.

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Martin Instructor
Burnaby, British Columbia
Martin Default
 

Exactly Eric!

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Raymond Mechanic
Midland, Michigan
Raymond Default
 

The code indicates a circuit fault. I would check for some steady ac voltage at the sensor connector while steadily rotating the wheel. You should not see a dc power/ ground relationship with the sensors. I would test the circuit with an ohmmeter if you see ac voltage.

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Brian Owner/Technician
Detroit Lakes, Minnesota
Brian Default
 

And... you are incorrect with your response.

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David Owner/Technician
St. Albert, Alberta
David Default
 

I think you are saying when you disconnect the RR sensor and put your voltmeter onto the harness side you do not have greater than 10V, It will not work properly by doing what you are saying as you want to do. It sounds like you have a break in the circuit between the module and sensor? Did you try reading the voltage KOEO at pins 42 & 43 before condemning the module?

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Brian Owner/Technician
Detroit Lakes, Minnesota
Brian Default
 

the problem is the ground circuit inside the abs module please look at the wiring diagram. It clearly shows there is a battery feed and a ground for each sensor. I am simply going to move the ground for the right rear sensor over to the left rear ground (together). btw. this part is no longer available as it has been discontinued, and I am in no way going to go through the hassle of a used one.

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Brian Owner/Technician
Detroit Lakes, Minnesota
Brian Default
 

Fixed. Spliced the grounds together and system is working fine.

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David Owner/Technician
St. Albert, Alberta
David Default
 

I think this is a digital sensor, don't recall if it is pull up or pull down type. In that case, he module should not be a ground on the side you are looking at, it is a negative side signal either pulling a small voltage down or generating a small voltage up from the sensor itself. If this "fixed" your system, this is new information for me. Probably the left rear and right rear give the exact…

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Martin Instructor
Burnaby, British Columbia
Martin Default
 

Hi David. I don't work on brands other than GM, so don't have the need and ability to access to an alternate information system while working remotely from campus. However, my first step would be to determine which type of ABS WSS the system uses. The schematic really doesn't do much in technical terms other than to represent a WSS, which appears to have a permanent magnet with two poles sensing…

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David Owner/Technician
St. Albert, Alberta
David Default
 

I think some testing of the "good" sensors and wiring would have been a sensible plan. I do know that one should be digital, so 10 - 11 V on the feed side would be expected IMO. The signal wire would then go high or pull low from the sensor. Once I know which way, maybe use a resistive load like a test lamp, polarity matching high or low, tapping on the signal wire on the "bad" sensor circuitry…

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Martin Instructor
Burnaby, British Columbia
Martin Default
 

Agreed. The results of the current repair may be unpredictable in a panic braking or other ABS event. Yes, a test light ~ 100 Ω or end of line CAN Bus terminating resistor can serve well as resistive loads for testing active WSS as shown in the illustration and supporting images and video clip.

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Brian Owner/Technician
Detroit Lakes, Minnesota
Brian Resolution
 

fixed

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David Owner/Technician
St. Albert, Alberta
David Default
 

NO, I don't think so. Everything you have said is unlikely.

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