'99 SD 7.3 ABS code B1485 w/ABS light - also intermittently un-locking the torque converter
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Tuned
Joined: Jul 2006
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From: Clover, SC
'99 SD 7.3 ABS code B1485 w/ABS light - also intermittently un-locking the torque converter
Trying to troubleshoot this problem - truck has a late '98 build date - F250 SD, 2wd automatic. ABS light has been on for awhile - comes and goes. Also it will intermittently - for no apparent reason - unlock the torque converter while cruising at highway speeds. It is returning DTC B1485, which is described as a malfunction of the brake pedal position switch. I suspect the transmission/torque converter malfunction is tied to this problem. Just wondering if anyone else has experienced this before and knows what the RX is. I figure it just needs a new BPS, but I want to make sure. Thanks in advance for any input.
Edit: There is a TSB on this (13927) but I can't seem to find a copy of it - just a summary.
Edit: There is a TSB on this (13927) but I can't seem to find a copy of it - just a summary.
Cargo Master
Joined: Mar 2006
Posts: 2,502
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From: Bend Oregon
Sounds like 2 different issues to me.
When the torque converter unlocks does the cruise control also disengage? That would definaty say break switch to me.
The ABS light is probibly an intermittant ABS sensor. You will need a code reader that can scan the ABS module to determine which one.
When the torque converter unlocks does the cruise control also disengage? That would definaty say break switch to me.
The ABS light is probibly an intermittant ABS sensor. You will need a code reader that can scan the ABS module to determine which one.
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Tuned
Joined: Jul 2006
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From: Clover, SC
Sounds like 2 different issues to me.
When the torque converter unlocks does the cruise control also disengage? That would definaty say break switch to me.
The ABS light is probibly an intermittant ABS sensor. You will need a code reader that can scan the ABS module to determine which one.
When the torque converter unlocks does the cruise control also disengage? That would definaty say break switch to me.
The ABS light is probibly an intermittant ABS sensor. You will need a code reader that can scan the ABS module to determine which one.
What I was hoping for here was for someone else who has had the same exact problem to chime in. To be sure this is a common issue if these brake pedal switches go bad frequently. There's a metric ***-ton of them on eBay - which is a good indicator to me that they fail commonly.
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Tuned
Joined: Jul 2006
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From: Clover, SC
Another question I have floating around in my head is how exactly does the circuitry associated with this switch work. It appears to be a microswitch - which tells me the load it directs is probably routed through a relay of some sort somewhere or possibly the BCM. I believe the harness that plugs into it has 5 wires in it, which also suggests it has multiple functions.
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Tuned
Joined: Jul 2006
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From: Clover, SC
Update - problem still not solved. I replaced the brake pedal position switch and the problem still persists. I can clear the B1485 code and go for a test drive and the ABS light comes back on just about as soon as I reach 20mph. Same code - B1485 - "brake pedal position switch short circuit to battery". I tried disconnecting the tow package harness, same thing. Tried disconnecting the taillight and center cab brake light circuits, same thing. When hooked up all the brake lights work fine. I am convinced that this code is also causing the trans to do silly ****. I really need some help on this one. Anyone?
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Tuned
Joined: Jul 2006
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From: Clover, SC
Also, this truck has never been wrecked or flooded and it has never been tampered with. It belongs to a 70yo man that bought it new and has taken good care of it. No hacked up wiring or aftermarket stuff spliced into the harness anywhere. It's completely stock and un-molested.
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Tuned
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You got the answer in your other thread about where the ABS module is located, but I want to encourage you to inspect the wiring harness that feeds that module.
Remove the airbox and driver's side battery entirely to get them out of your way.
Sometimes there are a couple of harnesses and/or hoses that come in contact with the front coil spring bucket / shock tower. I'd follow the path of the harness from the ABS module to the firewall first, before removing the ABS module, to see if there are any rub points that wore through the convoluted tubing of the harness wrap.
Black wire with light green trace is the more than likely the color code of the specific wire which indicates brake on or off.
Remove the airbox and driver's side battery entirely to get them out of your way.
Sometimes there are a couple of harnesses and/or hoses that come in contact with the front coil spring bucket / shock tower. I'd follow the path of the harness from the ABS module to the firewall first, before removing the ABS module, to see if there are any rub points that wore through the convoluted tubing of the harness wrap.
Black wire with light green trace is the more than likely the color code of the specific wire which indicates brake on or off.
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Tuned
Joined: Jul 2006
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From: Clover, SC
You got the answer in your other thread about where the ABS module is located, but I want to encourage you to inspect the wiring harness that feeds that module.
Remove the airbox and driver's side battery entirely to get them out of your way.
Sometimes there are a couple of harnesses and/or hoses that come in contact with the front coil spring bucket / shock tower. I'd follow the path of the harness from the ABS module to the firewall first, before removing the ABS module, to see if there are any rub points that wore through the convoluted tubing of the harness wrap.
Black wire with light green trace is the more than likely the color code of the specific wire which indicates brake on or off.
Remove the airbox and driver's side battery entirely to get them out of your way.
Sometimes there are a couple of harnesses and/or hoses that come in contact with the front coil spring bucket / shock tower. I'd follow the path of the harness from the ABS module to the firewall first, before removing the ABS module, to see if there are any rub points that wore through the convoluted tubing of the harness wrap.
Black wire with light green trace is the more than likely the color code of the specific wire which indicates brake on or off.
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Tuned
Joined: Jul 2006
Posts: 284
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From: Clover, SC
Well - no signs of chaffing on this harness. It was routed at the top of the inner fenderwell, not down on the frame/shock tower. It appears to be in good shape. I guess I need a schematic. I even took apart all the connectors on the ABS module to inspect for corrosion. Everything looks good.
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Has the brake switch on the master cylinder been replaced yet with the kind that doesn't have the membrane tear failure that caused brake fluid to come in contact with a constantly hot circuit that leads to trucks burning to the ground and led to a multi million unit recall by Ford to add fusible links to the circuit and ultimately replace the bad switch?
The recall is entitled "speed control", but it really is a brake switch failure... but calling a recall "Brake switch failure" sounds a lot scarier than an unnecessary function like "cruise" or "speed control". The failed part is a switch on the brake master cylinder that senses when fluid pressure has changed, indicating the service brakes have been activated. It is a switch made by Texas Instruments, and NHTSA evaluated the heck out of it, finally forcing Ford to recall it. Since it is a recall, the parts are cheap... less than $20 bucks delivered.
Since you are in there, you might as well see if that was done. The subject of brake switch made me think of it.
The recall is entitled "speed control", but it really is a brake switch failure... but calling a recall "Brake switch failure" sounds a lot scarier than an unnecessary function like "cruise" or "speed control". The failed part is a switch on the brake master cylinder that senses when fluid pressure has changed, indicating the service brakes have been activated. It is a switch made by Texas Instruments, and NHTSA evaluated the heck out of it, finally forcing Ford to recall it. Since it is a recall, the parts are cheap... less than $20 bucks delivered.
Since you are in there, you might as well see if that was done. The subject of brake switch made me think of it.
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Tuned
Joined: Jul 2006
Posts: 284
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From: Clover, SC
This switch you speak of is actually called the "cruise control release switch". It has nothing to do with the problem this truck has based on the troubleshooting I have done. I am now fairly certain the ABS module is bad. The ABS light turns on precisely at 22-23mph, every time. I'm guessing this is probably the speed at which the ABS module becomes active in the control loop. The light turns out and resets with an ignition switch cycle. The DTC it returns is always B1485 - brake pedal position switch short to circuit to battery. I have checked all the wiring, both for resistance and for voltage and it checks out ok. The short circuit has to be occurring within the module itself once it switches on. Also - the fact that the light is turning on at a precise speed every time tells me that it is a function of logic and not a mechanical fault. It has to be the ABS module.
Edit: Thanks for all your input though. It has been helpful.
Edit: Thanks for all your input though. It has been helpful.
Hotshot
Joined: Mar 2014
Posts: 10,750
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From: Douglassville, PA
Ever since my tranny was rebuilt the TC does the same thing when I first get up to highway speeds. I shift to neutral and back into gear and it stops. No resolution to the problem as of yet.
6th Gear
Joined: Jul 2024
Posts: 6
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Throttle position sensor ????
Trying to troubleshoot this problem - truck has a late '98 build date - F250 SD, 2wd automatic. ABS light has been on for awhile - comes and goes. Also it will intermittently - for no apparent reason - unlock the torque converter while cruising at highway speeds. It is returning DTC B1485, which is described as a malfunction of the brake pedal position switch. I suspect the transmission/torque converter malfunction is tied to this problem. Just wondering if anyone else has experienced this before and knows what the RX is. I figure it just needs a new BPS, but I want to make sure. Thanks in advance for any input.
Edit: There is a TSB on this (13927) but I can't seem to find a copy of it - just a summary.
Edit: There is a TSB on this (13927) but I can't seem to find a copy of it - just a summary.
i didn’t see the date on your post but I’d be interested in learning if that $50 sensor was causing it.
did in mine
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