'03 savana abs code


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May 26, 2022
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Bought an '03 Savana 3500 cargo van a couple of years back with a newly installed reman 6.0L gas engine. Van had a lot of things that pointed to an inept mechanic or two having worked on it over the years: stripped transmission pan drain plug, a bunch of loose or missing bolts here and there, a botched rear wheel seal repair, blown shocks etc... I went over it pretty well, put a couple of grand into it, and it's been behaving well ever since...until last week...

Been getting the abs and check engine christmas tree from time to time. On the engine side of things, it's a repeated P0122 and P1122. I'm planning on renewing the TPS, as I have one on hand, and the one on the truck appears to have been there for every single one of the 175K miles on the truck.

On the ABS side of things, it pops a C0040. Looking this up, I get conflicting information. On my scan tool, it says: "Rear Wheel Speed Sensor (Subfault)". That code, when you look it up elsewhere, says "right front wheel sensor"- so I'm a bit confused by that one.

It appears that the truck doesn't have legitimate rear wheel sensors in the ABS system. It looks to me like there are two identical sensors on the side of the transmission: an input, and an output sensor. I'm assuming that the rearward one would be the one that communicates with the ABS system, but I'm not 100% on that.
Anyone ever come across this before? The trans, a 4L80E- also appears to be original to the truck, so it wouldn't hurt to replace both of the sensors- they're cheap enough, but I want to make sure I'm not barking up the wrong tree before I do it for nothing...