Hey ya'll -- I have some questions regarding the ABS module logic and how it inputs the data from the rear axle sensor on the E350 differential pumpkin and turns it into the Rear Wheel Speed Sensor Reading (PID: R_WSPD). I am working on a 2000 E350 7.3L, which has a 3 sensor "system (one on each front wheel and one on the rear differential).

So far I've determined these sensors are the "passive" type -- the service manual states the circuit basically "involves a variable reluctance sensor and a tooth speed indicator ring to determine wheel speed". Well this is fine and dandy -- I get it -- when the tone ring spins, the sensor creates AC voltage, which is then sent to the 4WABS module to convert this signal to the "Rear Wheel Speed Sensor Reading".

But how does the 4WABS module conduct this this "conversion"? Does the 4WABS module read the AC voltage or the number of ac pulses or hertz? Does it read both?

Here's what the manual says:


This makes it seem like it is the number of pulses -- but if the number of pulses is directly proportional to some AC voltage for this given sensor system -- then it could just be reading the voltage.

The reason I am asking is I am 4x4 swapping an E350 van and the rear axle I'm using from a 2016 F350 doesn't have a tone ring on the carrier or provisions for a ABS sensor there. My idea to solve this problem is to put a tone ring on the rear output shaft of my transfer case. However, I'm trying to determine if I need to provide the right number of "pulses" or the correct AC voltage (or both) to the 4WABS module to make this work.

If it is just pulses or hertz -- I can accomplish this quite easily -- I will have 4.30 gears so a 28 tooth tone ring on the output shaft is roughly equivalent to a 120 tooth tone ring on the rear carrier (120/4.3 = 27.906 ~= 28). However, if I ALSO need to match the voltage -- things get more complicated since the voltage output is determined by the type of sensor, the characteristics of the tone ring (shape, type of metal, etc.) and the air gap between the sensor and ring and (of course) the number of pulses.

Given that speedometer adjustment devices like the Abbott ERA and the Dakota SGI-5E talk about translating "pulses" -- my hunch is the ABS computer is simply measuring the "pulses" or hertz of the AC signal. But after digging for a couple days, I haven't found any documentation about how this conversion takes place inside the 4WABS computer. I am hoping someone on FTE knows what goes on inside the 4WABS black box, so I can verify what I need to do before spending a bunch of time modifying my transfer case for a tone ring!

 

The PCM reads the "up" (or is it the "down," I never remember) pulse from the square wave generated by the sensor. It does not look at the voltage.

When I was at Ford and we were supplying transmissions to an off road race team, their axle didn't have a tone ring. We made a tone ring mounted on the trans output shaft that was 120/(rear axle ratio) number of teeth and it worked fine.

 

Thank you Mark! Very nice to know this will work!