2002 Ram 1500 w/4.7L 4WD crew cab manual trans: Cruising to work the other morning on the freeway - I heard a chime, looked down and saw my ABS (amber) and the BRAKE (Red) lights on. Today, the scan tool sees a fault, but when expanding the screen it only says "Foundation Brake" with no fault listed. The data stream shows the brake switch correctly as I pump the pedal, but all other components (including the ISO and Dump valves) never change state (probably because I was sitting in the driveway and there was no wheel speed input). The two fuses (6 and 35) were testing good. Are there any tricks to unlocking the connector to the CAB? It's really tight up in that corner of the engine bay. I was hoping to check powers and grounds to the controller, but left a considerable amount of knuckle skin on the fender.

 

Many scan tools won't show abs codes. You'll likely need to get a more fully featured scan tool to see what is going on.

 

My scan tool will read ABS - at least on other vehicles. On this one it will show the open or closed state of the valves (Isolation and Dump) as well as the state of the brake pedal and fluid level switches. It's like the ABS module the tool is trying to read is just dead. A couple of days ago (one time only) after I reseated the connector on the module, I noticed one of the parameters the scan tool was monitoring was the "Power Relay". When the ABS and Brake lights reset and everything seemed to be working (briefly) the relay showed "closed". Now with it not working again, the relay shows Open, and the Isolation and Dump valves are always closed. The wiring diagram from my service manual doesn't show a relay in the system - I'm wondering if the Power Relay is internal to the module and I'll just have to bite the bullet and get a new one ($300 to $400 plus programming).
On a side note, I checked powers and grounds (multiple wires going to the module), and everything checked good. There's a speed input as well, and my scan tool was reading an accurate MPH on the screen.

 

So, the wiring diagram from my county library auto repair resource (from MOTOR) shows three contacts within the brake pedal switch. In the drawing, the particular contact feeding the CAB (controller) is showing closed in the resting state. However, another printout from Alldata shows that contact inside the switch as open in the resting state! I'm not sure which one to believe. At rest, with the truck off and the connector of the controller removed, pin 9 (white/pink wire) is actually showing continuity to ground through the switch, which implies the library website is correct, not Alldata - unless the switch is actually bad.
It's a work in progress, and I'm slow - but eventually the answer will come. I'm actually leaning away from the controller, and more toward either a bad switch, sensor, or wiring.

 

Still trying to figure it out - no answers yet. There are 14 pins on the ABS controller - 11 are actually used in my application. Powers, Grounds, and 3 inputs (brake fluid level, rear speed sensor, and brake pedal switch) have all been checked. I even went so far as using my cheap oscilloscope to see the AC waveform of the rear sensor output on the ABS controller connector located under the hood, so I'm fairly confident that part is ok (Speedometer works fine). Then I isolated all the output wiring and applied 12 volts while checking for a voltage drop under load (I used a fairly high amp-draw light bulb). The wiring checks ok.
Except I haven't yet checked the two "outputs" from the controller - the PCI bus wire which turns the ABS/Brake lights on in the dash, as well as providing a signal to the OBD connector, and the other one is the vehicle speed signal which originates from the rear sensor and goes to the controller, then on to the PCM, which provides a speed signal to the speedometer, among other things (again, the speedometer works fine, so I'm inclined to think that part is ok).
I do have a "Loss Of JTEC (#35) J1850" message as part of my scan tool readings. The J1850 bus (this vehicle doesn't have a CAN bus) appears to be the same thing as a PCI bus labeled in the wiring diagrams. That's just a single wire output going to the dash as I mentioned earlier, so that's where I'm going next.

Or I could just take it in and let the dealer diagnose it, and probably just change the controller...

 

I would consider replacing the rear wheel antilock speed sensor. I know you have checked it. A faulty sensor will give you the indications you describe.
Just a rec, it's inexpensive and often seems to be the fix to confusing brake problems.

 

Take it somewhere that can read abs codes, and see what it is whining about.

 

The speed signal originates from the sensor, through the ABS controller, then to the PCM, then to the speedometer. The speedometer works fine, and also the real time data in my scan tool shows vehicle speed correctly, I was getting a valid signal with the automotive oscilloscope which showed the A/C signal output of the sensor as read from the controller connector. My scan tool shows 2 faults. When expanding the screen on the scan tool, the first fault is just blank - no data. The second fault shows an open speed sensor fault, which makes no sense based on my prior testing. The wires have continuity and check ok with respect to both ground and with each other. They are also able to carry a heavy load.

So I bought a new sensor anyway - no help.

The J1850 bus wire to the PCM I looked at earlier checks good.

In my mind, there's nothing left but the controller.

 

I guess I should note here that if anyone looking at this later has similar issues, my application will probably be different since I have a manual transmission. I think (but not sure) that the automatic transmissions have a separate sensor in the transmission.

 

2 or 4 wheel ABS? Can you see what the other sensors are reporting??