False ABS, C1230
Thread Starter
Junior Member
Joined: Mar 2014
Posts: 20
Likes: 1
False ABS, C1230
Hey gang, here's a stumper for you... This is on my '05 FX4 SCrew, ~120 kmi.
First off, the only place I could find someone else with exactly the same problem as me is here:
http://www.f150online.com/forums/200...t-sliding.html
Unfortunately, it doesn't look like anybody there reached a resolution.
In a nutshell, the ABS is kicking in when braking in dry/no-slip conditions, then within a second or two the system realizes it didn't need to engage, and disables itself, at which point the ABS light pops on and stays lit. There doesn't seem to be any rhyme or reason to when the ABS erroneously activates. Sometimes it'll do it when braking hard from highway speeds, sometimes it'll go when braking lightly from 20 mph or less. Most frequently it seems to need to get up to highway speed first before having issues, but again, sometimes it'll go when I'm braking hard at 50-60 mph, and sometimes it'll be fine until I get below 30, then it'll trip. The ABS is definitely firing when it occurs, as I can hear the pump and feel it in the brake pedal.
When I shut the truck off and restart it, the "condition" is cleared, and the ABS light is off. However, after driving around for a little bit and hitting whatever the critical condition is, the ABS will again kick in when it doesn't need to, then disable itself, illuminate the ABS light, and it'll stay that way until I again shut the truck off.
I've got a Bluetooth OBDII scanner, and that gives me a C1230 DTC (ABS light doesn't have to be on for the code to read), and that's it. I keep reading that there are alternate/special/magical "ABS codes", but my reader can't pull those (Does anybody know if the readers that Advance/O'reilly/Autozone usually have on hand these days will read them?). That code is something like "rear speed sensor circuit fault", which 95% of the relevant internet reports as being a problem with the rear speed sensor in the rear diff. I also read that, if you measure the resistance of that sensor, it's supposed to be around 5 Mohm, plus or minus a couple Mohm. My DMM read it as an open circuit, so I figured that was my issue as well.
Picked up a new sensor ($80, yeesh), and oddly, it measured as an open circuit as well... Went ahead and popped it in, and I was still having the same problem, so I thought I must have gotten a bad sensor. The parts store let me exchange it for free, but even the second new sensor read as an open circuit. Clearly something was amiss...
This is a bit of a tangent, but here's my soap box speech about using quality equipment... About a year ago, I had bought what I *thought* was a quality DMM - it was an auto-ranging Masstech, and it ran me about $40. My buddy has a Fluke, which is the best of the best (but the low-end models run around $150-$200), and he let me borrow it. Sure enough, it reads ~5 Mohm on the new sensor, even though my Masstech says it's an open (even when I manually set it to high range). Moral of the story, if you're not using a Fluke DMM, you're doing it wrong.
I still had the old sensor, and it read ~4 Mohm as well (with the Fluke, of course), so plainly the sensor was not my problem. I found a pinout diagram for the ABS module harness, and checked continuity from there down to the sensor pigtail (while wiggling away on the pigtail wires), and that seemed to be just fine as well (no shorts, either). I then checked the voltage across the pigtail connectors with the key in and turned to ACC, and I read 9.5 V, which is right around where it's supposed to be (I read that 9 V is the desired value, half a volt off doesn't seem bad to me).
I've had the truck for five years now, and haven't done anything as far as brake maintenance. The back end was getting a little squirrely on me when braking from highway speeds, so I knew the front rotors were probably getting warped. I also had a fair amount of pedal travel, so the pads were probably getting low, too. My next thought (hope) was that this was the cause of my ABS issue.
Just finished a full brake job last night, new pads all around, freshly turned front rotors, and brand spanking new back ones. The old pads weren't *too* bad, but they did have to turn the front rotors a fair amount, and there wasn't enough left of the backs to turn (hence the new ones). Took it for a spin after I got everything back together, and the hoppy back end was definitely gone. Braked HARD a couple of times from highway speed (enough to get just a hint of tire squeal), and everything acted fine. Pulled into a gravel lot to check that the ABS was still functioning as intended, and sure enough, on a hard brake, it kicked in as expected (with no light). I still wasn't completely convinced though, so I pulled back onto the highway. I then came to a "normal" stop at a red light, and it tripped again once again once I got down to about 30 mph. Read the code when I got back home just for funzies, and it's still the same, C1230.
I also had the thought that the tone ring in the diff might be chipped/cracked, so I popped the speed sensor back out, stuck an inspection cam down there, and gave the wheels a slow turn (with the back end up on stands, obviously). Turned it enough to see the whole ring go around a couple of times, and I didn't see anything that stood out. Looked like there was plenty of fluid in there, too.
My last hope that it's not the electronic ABS module (a ~$700 fix, per a conversation with my dealership) is that the connectors in the pigtail are actually dirty or "loose", and that's bouncing around enough when driving to cause signal problems. I can get a new pigtail for about $20, so I'm going to give that a try over the weekend.
Does anybody have any further thoughts on this one? Sorry for the encyclopedia, but I wanted to make sure to list out everything that I've already tried.
First off, the only place I could find someone else with exactly the same problem as me is here:
http://www.f150online.com/forums/200...t-sliding.html
Unfortunately, it doesn't look like anybody there reached a resolution.
In a nutshell, the ABS is kicking in when braking in dry/no-slip conditions, then within a second or two the system realizes it didn't need to engage, and disables itself, at which point the ABS light pops on and stays lit. There doesn't seem to be any rhyme or reason to when the ABS erroneously activates. Sometimes it'll do it when braking hard from highway speeds, sometimes it'll go when braking lightly from 20 mph or less. Most frequently it seems to need to get up to highway speed first before having issues, but again, sometimes it'll go when I'm braking hard at 50-60 mph, and sometimes it'll be fine until I get below 30, then it'll trip. The ABS is definitely firing when it occurs, as I can hear the pump and feel it in the brake pedal.
When I shut the truck off and restart it, the "condition" is cleared, and the ABS light is off. However, after driving around for a little bit and hitting whatever the critical condition is, the ABS will again kick in when it doesn't need to, then disable itself, illuminate the ABS light, and it'll stay that way until I again shut the truck off.
I've got a Bluetooth OBDII scanner, and that gives me a C1230 DTC (ABS light doesn't have to be on for the code to read), and that's it. I keep reading that there are alternate/special/magical "ABS codes", but my reader can't pull those (Does anybody know if the readers that Advance/O'reilly/Autozone usually have on hand these days will read them?). That code is something like "rear speed sensor circuit fault", which 95% of the relevant internet reports as being a problem with the rear speed sensor in the rear diff. I also read that, if you measure the resistance of that sensor, it's supposed to be around 5 Mohm, plus or minus a couple Mohm. My DMM read it as an open circuit, so I figured that was my issue as well.
Picked up a new sensor ($80, yeesh), and oddly, it measured as an open circuit as well... Went ahead and popped it in, and I was still having the same problem, so I thought I must have gotten a bad sensor. The parts store let me exchange it for free, but even the second new sensor read as an open circuit. Clearly something was amiss...
This is a bit of a tangent, but here's my soap box speech about using quality equipment... About a year ago, I had bought what I *thought* was a quality DMM - it was an auto-ranging Masstech, and it ran me about $40. My buddy has a Fluke, which is the best of the best (but the low-end models run around $150-$200), and he let me borrow it. Sure enough, it reads ~5 Mohm on the new sensor, even though my Masstech says it's an open (even when I manually set it to high range). Moral of the story, if you're not using a Fluke DMM, you're doing it wrong.
I still had the old sensor, and it read ~4 Mohm as well (with the Fluke, of course), so plainly the sensor was not my problem. I found a pinout diagram for the ABS module harness, and checked continuity from there down to the sensor pigtail (while wiggling away on the pigtail wires), and that seemed to be just fine as well (no shorts, either). I then checked the voltage across the pigtail connectors with the key in and turned to ACC, and I read 9.5 V, which is right around where it's supposed to be (I read that 9 V is the desired value, half a volt off doesn't seem bad to me).
I've had the truck for five years now, and haven't done anything as far as brake maintenance. The back end was getting a little squirrely on me when braking from highway speeds, so I knew the front rotors were probably getting warped. I also had a fair amount of pedal travel, so the pads were probably getting low, too. My next thought (hope) was that this was the cause of my ABS issue.
Just finished a full brake job last night, new pads all around, freshly turned front rotors, and brand spanking new back ones. The old pads weren't *too* bad, but they did have to turn the front rotors a fair amount, and there wasn't enough left of the backs to turn (hence the new ones). Took it for a spin after I got everything back together, and the hoppy back end was definitely gone. Braked HARD a couple of times from highway speed (enough to get just a hint of tire squeal), and everything acted fine. Pulled into a gravel lot to check that the ABS was still functioning as intended, and sure enough, on a hard brake, it kicked in as expected (with no light). I still wasn't completely convinced though, so I pulled back onto the highway. I then came to a "normal" stop at a red light, and it tripped again once again once I got down to about 30 mph. Read the code when I got back home just for funzies, and it's still the same, C1230.
I also had the thought that the tone ring in the diff might be chipped/cracked, so I popped the speed sensor back out, stuck an inspection cam down there, and gave the wheels a slow turn (with the back end up on stands, obviously). Turned it enough to see the whole ring go around a couple of times, and I didn't see anything that stood out. Looked like there was plenty of fluid in there, too.
My last hope that it's not the electronic ABS module (a ~$700 fix, per a conversation with my dealership) is that the connectors in the pigtail are actually dirty or "loose", and that's bouncing around enough when driving to cause signal problems. I can get a new pigtail for about $20, so I'm going to give that a try over the weekend.
Does anybody have any further thoughts on this one? Sorry for the encyclopedia, but I wanted to make sure to list out everything that I've already tried.
Thread Starter
Junior Member
Joined: Mar 2014
Posts: 20
Likes: 1
A small update...
Ended up not buying a new pigtail... Did one more "continuity test" by unplugging the rear speed sensor and starting the truck up, and the ABS light comes on right away and stays that way. Plugged the sensor back in, started the truck back up, and the light was back off. I guess if there's an intermittence back there, that could still be causing signal issues, but as I mentioned, the back end isn't "hoppy" anymore on braking, so I don't think that's my problem.
Got the wheels balanced over the weekend, but I didn't have any bad vibrations from them before, so that didn't fix the problem.
Had the codes read by the guys at my local Advance, and they said their reader *would* read ABS codes. "Rear wheel speed sensor." Crap.
I've got an appointment with the dealership Tue morning for a diagnosis. I'm fairly certain it's the electronic ABS control module.
Ended up not buying a new pigtail... Did one more "continuity test" by unplugging the rear speed sensor and starting the truck up, and the ABS light comes on right away and stays that way. Plugged the sensor back in, started the truck back up, and the light was back off. I guess if there's an intermittence back there, that could still be causing signal issues, but as I mentioned, the back end isn't "hoppy" anymore on braking, so I don't think that's my problem.
Got the wheels balanced over the weekend, but I didn't have any bad vibrations from them before, so that didn't fix the problem.
Had the codes read by the guys at my local Advance, and they said their reader *would* read ABS codes. "Rear wheel speed sensor." Crap.
I've got an appointment with the dealership Tue morning for a diagnosis. I'm fairly certain it's the electronic ABS control module.
Thread Starter
Junior Member
Joined: Mar 2014
Posts: 20
Likes: 1
Just got the truck back from the dealership...
Problem ended up being wiring. The wires for that rear sensor were rubbing against the driver's side exhaust (I have dual, 1-in 2-out muffler) and had worn through. It was still a pricey fix from the dealership, but was ALOT cheaper than the $700 bill I was expecting for a new ABS module.
Problem ended up being wiring. The wires for that rear sensor were rubbing against the driver's side exhaust (I have dual, 1-in 2-out muffler) and had worn through. It was still a pricey fix from the dealership, but was ALOT cheaper than the $700 bill I was expecting for a new ABS module.
