Dealer Techs , ABS light on a 98 ram 2500

I just got a new 2 me 98 2500 Cummins Ram , RWD. The ABS light on the dash is flashing, only the ABS light . Everything I read on line say the ABS light and the brake light flash together , mine does not . It has code 37 according to the Ford dealer that I bought it from. Code 37 doing an online search is for the rear axle mounted speed sensor, it's a cheap enough part to replace.

I've also read that if the underhood CAB is replaced it needs to be reset with a DRBIII tool , is this the case ?

Thanks

That's the way our '98 acts. When it gets really cold (-10 or colder) the ABS light comes on. Same code, rear differential sensor. Warms up, goes away.

90 percent of the time its the wiring going to the sensor that breaks down, You can ohm the sensor out to prove it. Birdtracker

Similar on my 96. When sensor was cold, would fail on startup. Warm would work. Sensor is an easy fix. Old one was stuck in there pretty good. Blow off the dirt and debris before you pull off to prevent junk from falling in.

John two common items are the sensor and the other is the wiring, Common area up along the frame where the harness can flex with the suspension extending.

Thanks guys , I'm going to get it up on a lift at lunch so I can get a good look at the wiring .

The odd thing I notice is the ABS light is flashing all the time once the dash self check is finished, whether the engine is running or not , moving or not , no brake warning light . I have no history on what's been done to the truck , bought it on line 1600 miles from where I live so this should be interesting.

John, sans an OBD scanner a lot of Chrysler products can be self-scanned with the key on/off cycle like in this video. Some models will display the codes and some earlier models used the "blink" codes for self-diagnostics. Most local auto parts stores will clear the codes or reset the OBD for you no charge. The self-scan key on/off method just helps as a quick check to see if what's going on. Hope this works for your RAM and hope it helps.

I tried that expecting a code in the odometer window and there was none. I didn't pay attention to the CEL light, which was how one of my older rams spit out a code... I'll give that a shot . When I put an Actron scanner on it no codes were present ?

As I recall, ABS in these years is a completely separate system, specialized equipment is required to diagnose them. Rear axle sensors were first used in 1998.

Not sure on a 98 but my on 01 I can hold down the odometer trip button then turn ignition on then release button and dash will self check and codes will show in the odometer place.

To get ABS codes you have to ground out on of the pins on the OSD2 connector. The ABS light will flash and give you the code/s. Don't know what pin or the flash count you have to look in the factor service manual for that.

I crawled under the truck and see that the sensor has been replaced, I ohmed it and it is not open so I'm guessing that a wire is broken somewhere ?

Looking under the hood where the CAB is for the RWAL system there is a connector that is not connected to anything and there is nothing not connected on the control board. I really need to find a wiring diagram for this thing .

You can download the FSM here. Handy if you have a tablet to take out to the garage.

https://www.ramforumz.com/threads/all-2nd-gen-service-manuals-in-pdf.234888/

Thanks , I found the FSM online , downloaded the schematic and pages on RWAL, the extra connector is for trucks with 4 wheel ABS.

I was able to test the rear sensor up to the controller under the hood and I have continuity and the same reading I had under the truck. I also checked the grounds and supply voltages and all are present. Just need to pull the code , but I think it's the control head that is the issue ?

I was also given the idea to check the sensor with an non digital ohm meter , spin the rear axle and see if the needle sweeps up and down?

I'm noticing that the peddle does pulse when I stop, so something is going on.

I could just bypass it and pull the bulb but I really want to fix it .

Get the codes pulled. It could be a problem in one front circuit. The code should help narrow it down.

It's rear wheel only ABS , tomorrow I'm going ground pin 13 on the ODBII connector and read the number of times the light flashes.

I wish I had access to a DRB scan tool.

Pull that sensor out and take a peek. It's a magnet so any metal floating around in the rear will collect on it and cause errant signals. Missing/chipped/broken teeth on the trigger wheel will cause the same. Graph or lab scope will show that stuff as well. Good luck...hope it's an easy fix!

Last night I picked up an Innova scanner that could see the ABS codes . I have 4 ,

37 , erratic rear sensor signal

47 shorted iso solenoid or open ecu output, LF

45 open iso solenoid or shorted ecu output, LF

65 open power relay contacts

I can't find anything in my 2000 FSM that mentions anything about these codes ? Google here I come .

if i recall, those codes usually show up when antilock ecu is bad. again if i recall those ecu's are not avail new or from dealer. usually a bone yard and it is a crap shoot getting a good one. might be differeny now but that was how it used to be.

If you end up needing a ecu for the antilock brakes check ebay. I seen some on there recently.

That is my thought , it just flashes the ABS light only, continually as soon as you turn on the ignition. Used is my only source , fingers crossed I can find a good one .

There are many on ebay , the problem is unless I can find one from a truck like the truck i have , dana 70 and 245 65 16 tires , i need to reprogram it .

thanks for everyones help so far.

Abs ecu is bad common problem in those trucks.

I believe this is the case , I learned more about how the system interacts with the PCM accidently .

Yesterday while trying to trouble shoot it I pulled out the CAB and tried to open it up , which was unsuccessful. I gave up tryingto open it without damaging it and just tossed it on the front seat of the truck and cleaned up to go out to dinner. This morning I went out in the truck and noticed the ABS light was still on , same as if the fuses were pulled , but this time the brake warning light was also on , it's never been on other than during the cluster self check, but I suddenly noticed that the speedo was not reading , what the ?? I did pull the rear end sensor to check for debris or damage but I never unplugged it , once I got to a safe place to stop I reinstalled the CAB unit , the speedo is now working again and the abs light and the brake light are on solid, I did not reconnect the solenoid unit. when I got to where I was going I reconnected the solenoid unit and the brake light went off and the abs light was once again flashing. This is telling me the solenoid is good and the CAB is the problem.

Now to find another cab and hopefully not have to pay a dealer 152 dollars to reset the rear end and tire size codes .

Does the truck have a posi rear?

limited slip ... yes