[FIXED] 2008 F 150 Rear wheel speed fun

2008 Ford F150 with 82,000 miles.
Customer complaint of ABS lamp on.
Scanned for codes, found several referring to lost left front speed signal and lost rear wheel speed signal.
Found broken wire at L.F. connector, repaired and cleared codes.
Now for the fun part.
Put it in drive and the ABS lamp comes on again. More specifically, step on the brake and the ABS lamp comes on.
C1230: rear wheel speed sensor circuit fault
C1273: rear wheel speed sensor input signal missing.
Run it on the lift in 4x4 and sure enough, no speed signal. Scope the sensor, no signal. So she gets a new sensor.
I'll save some space here and explain that the sensors on this get a 12v feed from the EBCM unless there is a fault. So if you disconnect a sensor to check voltage, you won't see it because a code sets and the EBCM stops sending power to that sensor.
It took me some time to figure that out, but whatever. So with the sensor connected, codes cleared, probing both wires of the rear wheel speed sensor I get 10 volts. Perfect. Step on the brake, lose voltage at the sensor and EBCM (abs) sets c1230 & c1237 again...
If I clear the codes and start the truck in neutral and shift to drive without touching the brake, no problem. No codes and all wheel speed sensors are operational.
More fun!
Turning on the four way flashers also sets the codes in the ABS module.
Using the left directional sets the codes and kills the rear wheel speed sensor.
With the left tail lamp disconnected, turning on the left directional does not set the codes, however pressing the brake or the hazard lamps still does.
The brake pedal position switch is a 4 wire switch.
Jumping the 2 green wires sets the codes, but the jumping the other two does not. So the fault is related directly to that circuit. However, this is not a direct input to the EBCM.
I have disconnected the trailer harness, the trailer brake control module and all the stop lamps to no avail.
The boss wants to try an ABS module, so he's buying one today, but I don't have the confidence to make that call based on what I've found so far.
Any advice or ideas would be much appreciated.
I'll be sure to update with my progress, but this truck is going on the back burner to get some money jobs done.

“ Using the left directional sets the codes and kills the rear wheel speed sensor.
With the left tail lamp disconnected, turning on the left directional does not set the codes, however pressing the brake or the hazard lamps still does.”

I’m choosing to latch onto this. I’m wondering if it’s a ground issue on G110.

Well.... I have some ideas? But I dunno how good they'll be. :silly:

Like you said, there's no direct BOO input to the ABS. It comes networked from the PCM. So, I wonder what would happen if you disconnected the PCM, cleared the ABS codes and tried again?

It'll set U-codes, sure. But if you can hit the brakes and not set C1230/C1237, then I'd suggest that the problem has to do with the ABS module, and the BOO message from the PCM. If the codes reset, then I'd probably dig a little deeper into the RWSS circuit.

Maybe try a hard reset while you're off on other cars? Tie the battery cables together and let the truck think about what a stupid POS it's being.

If all else fails, maybe your boss is right? How about just electrically connecting a used module, do an As-Built inhale/exhale, and see if it's any happier. You'll get a motor code, but so what.

John Curtis wrote: “ Using the left directional sets the codes and kills the rear wheel speed sensor.
With the left tail lamp disconnected, turning on the left directional does not set the codes, however pressing the brake or the hazard lamps still does.”

I’m choosing to latch onto this. I’m wondering if it’s a ground issue on G110.

Thank you for taking the time to look into this and respond.
It's certainly not out of the question, I will look into it later today after I make some money for the shop and let you know what I see.

Tyler wrote: Well.... I have some ideas? But I dunno how good they'll be. :silly:

Like you said, there's no direct BOO input to the ABS. It comes networked from the PCM. So, I wonder what would happen if you disconnected the PCM, cleared the ABS codes and tried again?

It'll set U-codes, sure. But if you can hit the brakes and not set C1230/C1237, then I'd suggest that the problem has to do with the ABS module, and the BOO message from the PCM. If the codes reset, then I'd probably dig a little deeper into the RWSS circuit.

Maybe try a hard reset while you're off on other cars? Tie the battery cables together and let the truck think about what a stupid POS it's being.

If all else fails, maybe your boss is right? How about just electrically connecting a used module, do an As-Built inhale/exhale, and see if it's any happier. You'll get a motor code, but so what.

I isolated the green wire that is the input to the PCM with the intent of cutting it to test that theory yesterday but decided to exhaust other avenues first.

The battery cables are already connected to each other while I'm doing a brake job on a Benz and I intend to do just as you describe with the new/used brake module when it shows up.
Thanks for your support

I just don't understand why it's picking on the RWABS sensor only...
Weird stuff.

Noah wrote: I isolated the green wire that is the input to the PCM with the intent of cutting it to test that theory yesterday but decided to exhaust other avenues first.

Oooooh, that's even better. Never mind what I said.

The battery cables are already connected to each other while I'm doing a brake job on a Benz and I intend to do just as you describe with the new/used brake module when it shows up.

I figured you had one in the yard somewhere? Or is it not worth the time to extract one?

I just don't understand why it's picking on the RWABS sensor only...

I got nothin'. Was trying to think of a test you could do to determine if the ABS is genuinely detecting a circuit fault when the brakes go on (due to green crusties/water intrusion/resistive shorts/whatever). Running new wires would be too much work... Maybe disconnect the ABS and RWSS, scope on both wires, apply brakes, see if anything changes.

Apparently it's a high failure part as none of mine in the yard have one.

Have you scoped powers and grounds to the abs module when stepping on the brakes?? Maybe try unhooking the other 2 sensors and step on the brake see if it still kills the rear speed sensor. Sounds like an auction truck special. Or maybe even try de pinning the connector and swapping front abs sensor to rear terminals.

Cheryl wrote: Have you scoped powers and grounds to the abs module when stepping on the brakes?? Maybe try unhooking the other 2 sensors and step on the brake see if it still kills the rear speed sensor. Sounds like an auction truck special. Or maybe even try de pinning the connector and swapping front abs sensor to rear terminals.

Thanks for the reply Cheryl.
I only had a short time to test at the end of the day today.
I didn't scope the powers and grounds at the module but I did monitor them with a multimeter while setting the code by pressing the brake.
I never lost a feed or ground to the module during the fault
However the voltage output to the RWABS from the module on the vss+ goes from 10v to around 2v with the pedal depressed. At which time the codes set and the module stops powering the sensor until the next key cycle.
I forgot to mention in the first post that when I started testing this yesterday while I had the scan tool hooked up the rear wheel speed PID would jump around every time I pressed the brake pedal. I saw it jump as high as 85mph, key on engine off just tapping the brake pedal. I think I have the .vss file saved
There is an after market trailer brake controller that is wired into the provisional factory connector behind the dash, but I unplugged that yesterday with no improvement and left it that way for now.
After studying the diagrams some more, I figured I could divide the lamps circuit from the trailer circuit by removing fuse #42 from the central junction box.
With that fuse removed, the problem appears to be completely gone!
Disconnecting the trailer harness connector or the connector before it in the harness under the bed (c411) makes no difference.
So it would appear that the problem lies in an 8ft section of harness between the fuse panel in the cab and c411 over the rear axle.
According to the OEM power distribution diagram, fuse #42 goes from the fuse box to the trailer hitch connector only.

There's 2 more connectors under the cab where the harness exits the interior. I'll see if I can further divide the circuit from that point and hopefully over lay a new wire for what I'm assuming now must be a crossed circuit some where in the wire loom.
At least that's the plan for now. See what happens in the morning.

I did volt drop test the ground at g110 at the suggestion of John Curtis and can verify that this is a good ground.

Thank you everyone for your help so far:)

Well. I didn’t read your last post that thoroughly before I posted so, probably disregard what I posted below. I’m super exhausted and can’t focus well but am staying up due to severe weather and potential tornadoes.

If tapping the brake makes the rw sensor have a signal can you scope the sensor and see if you hold the brake pedal down if the signal will change speed or go away after a small amount of time? It’s kind of an out there idea but something you may want to consider ruling out, if depressing the brake pedal is causing the tone ring to shake slightly it might be enough to throw the signal out of wack. You would see that on a scope for sure. If that isn’t fruitful then I’d be throwing a module at it.

I hope that you and your loved ones are safe John.
I did electronically connect another module to try it, but the issue persisted.

So in my attempt to divide the circuit between the fuse panel and the trailer harness, I found that the larger of the two connectors on the frame under the drivers door had water intrusion, corroding multiple pins.

Both wires in the rear wheel speed sensor circuit run through that connector, as does the yellow wire that is shown going from fuse #42 to the trailer harness connector.
I cleaned both ends of the connector with contact cleaner and compressed air and added a small amount of dielectric and the symptom has not returned. The customer has been made aware of the condition and will decide what repair option he'd like us to pursue.

I am having a hard time relating the symptom to the fault however.

Even if there was voltage drop on the rear wheel speed sensor circuit in that connector, how would illumination of the hazard/flasher/brake lamps have any effect on that circuit?

Could the contacts have been shorted together via the small amount of water still present inside the connector?

Any Ideas or wisdom?

With other work coming in the door I didn't have time to investigate the issue further. I was attempting to ID that connector number to see what other circuits are run through the connector.

Thanks to everyone for reading and for helping. I really appreciate it.

Nice find!!!
You’re thought about the water shorting intrusion seems right. The only thing I could think of to have proven it would be to disconnect power and do a continuity check between wires/pins at the connector.

Thanks brother. the storm pretty much missed us. We’re in hill country which seems to be the least impacted by the weather. Although a tornado did pull off the ground about 3/4 miles from our property and went right over us on Easter. First time experiencing any crazy weather as I’ve only been in Tx for a short amount of time.

For any iATN members, here is a link to the discussion I posted over there.
autop.ro/q1r
I have never experienced a crossed circuit within a connector due to water intrusion. I always viewed terminal corrosion as resistance in a single circuit, I didn't realise that the moisture would bridge contacts.
Fundamentally it makes sense, but it's something I hadn't experienced until now.
Thanks again to everyone who replied!

Rear wheel speed sensor connector bypass

Looks like it should have that way from the factory

Andy.MacFadyen wrote: Looks like it should have that way from the factory

Thank you, a coworker got those connectors from Wish

Noah wrote: Thank you, a coworker got those connectors from Wish

Andy isn't kidding - that repair looks legit.

I dunno that I'd pick up on the repair during a visual inspection, unless I was looking for it.

Thank you. I'm going to look into buying an assortment of those connecters, I'm happy with the way it turned out.

SuperSeal ?