'03 Savana 3500 ABS light and code

[toonz]

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...

[MountainManJoe]

Hello. Welcome to the forum.

On the engine side of things, it's a repeated P0122 and P1122

TPS signal voltage is too low or intermittent.

Measure with meter to make sure it has 5.0V on the grey wire, ground on tan. Dark blue should sweep between below 1V and above 4V depending on throttle position.

C0040 means the EBCM is getting unexpected information from a front wheel speed sensor.

The most common causes are:

• Water intrusion
• Wiring broken inside the insulation
• Poor connection between the male and female terminal at a connector
• Poor terminal to wire connection -- some conditions that fall under this description are poor crimps, poor solder joints, crimping over the wire insulation rather than the wire itself and corrosion in the wire to terminal contact area.
• Wire insulation that is rubbed through -- this may cause an intermittent short as the bare area touches other wiring or parts of the vehicle.

Measured resistance across the wheel speed sensor should be in the range of 700-10,000 ohms.
Rotating the wheel by hand should produce a 100mV AC voltage from the sensor.

It appears that the truck doesn't have legitimate rear wheel sensors in the ABS system.

Your van only has front wheel ABS speed sensors (WSS).

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.

The transmission input and output speed sensors are used for controlling the transmission only.

[toonz]

I'm aware that the standard definition of code C0040 refers to the right front abs sensor- however, the definition that comes up for that code on my scan tool says: Rear Wheel Speed Sensor (Subfault). (see attached pic)- it appears to be a GM specific abs fault code...

...That's what I'm confused about...

[MountainManJoe]

the definition that comes up for that code on my scan tool says: Rear Wheel Speed Sensor

Everything I find suggests that there are no rear wheel speed sensors, and that DTC C0040 indicates a problem with the front sensors.
This is directly from GM.

[toonz]

Very strange that my scan tool would have the incorrect info for a code. When I look up "rear wheel speed sensor" for my year, make, and model- I get a lot of results that show the front sensors, and an equal amount that show the sensors I referred to on the side of the transmission.

I got a pair for $20 bucks, so I'm gonna put 'em in. If the light comes back, I'll troubleshoot the right front sensor. Easy enough to replace, and readily available, so...The TPS, I will troubleshoot during replacement, in case it's a bad plug connection or ground...

[MountainManJoe]

an equal amount that show the sensors I referred to on the side of the transmission.

I think if those weren't working, your speedometer wouldn't work and you would experience problems with shifting.

[toonz]

I do occasionally experience a hard 1-2 shift, almost like someone installed a shift kit. If I pull over and shut it off, it usually won't repeat on a restart.

I replaced the TPS, which went a lot smoother and faster than I thought. Didn't even have to pull the alternator.

I replaced the output VSS, but the input speed sensor does *not* want to come out of it's bore. I removed the single bolt that holds it in, and it would not slide out. I managed to get the bracket off of it, and spun it all the way around, but it absolutely refuses to come out. Lotta fun...

Rather than break it, I put the bracket back on and put the bolt back in.

I'll just have to wait and see if the light stays out. On a test drive, it acts no different than it ever did...

When pulling the output sensor, there is a plastic piece attached to the bracket that holds three steel lines. It didn't survive, snapping in half. I can't even find a picture of it in any diagram- would you happen to know what it's called? I'm off to the dealer tomorrow, to see if the parts guy can help me order a new one...

[MountainManJoe]

the input speed sensor does *not* want to come out of it's bore

Like I said. Input sensor has absolutely nothing to do with ABS.
If it aint broke, don't fix keep fixing it until it IS broken.

there is a plastic piece attached to the bracket that holds three steel lines.... would you happen to know what it's called?

brake lines?