Joey-D

Problem:
-Brake Light ((!)) is steady on. No ABS light, brake light only. OTC Genisys Reads as code 78 Base Brake System Incident


Truck:
-2003 Dodge 3500 4x4 Cummins Quad Cab Long Bed 6 Speed 248K


History:
-Bought the truck as a under hood fire. Replaced 2 wiring harness, the master cylinder, hydroboost Unit, ABS Pump, Battery, Clutch Master Cylinder and a few other small things that aren't important. All parts were off a used cummins. Truck started its life as a dually 3.73 truck, but I swap axles to my personal truck (this one is dealer owned) so now it is a single wheel 4.10 truck.


Since put back together:
-I had originally replaced the whole abs module and pump, but then had a brake and abs light on for a VIN Mismatch, since this was a used module. I replaced the module with the original one and the abs light went away. I have put 350 miles on this truck with the brake light on. ABS functions as it should. Brakes feel great.


Attempts to Fix:
-Vacuum Bleed the whole system. 300 mls (9 ounces) vacuumed through each of the rear calipers and 200 mls (6 ounces) vacuumed through each of the front calipers. No evidence of air in lines. This is 350 miles after the original gravity bleeding I did when I swapped axles.

-Swapped brake level sensors in the master cylinder with the one on my personal truck.

-Grounded and powered and adjusted the brake light switch on my the emergency brake lever. (On my personal cummins, when the e-brake is on, the light flashes on the dash, not a steady on)

-Erased codes via scanner.

-No brake related codes via dash scanning. (Key on off on off on)


Other Tidbits:
-Pads look good. Front rotors thin.

-ECM was hacked to removed SKIM system.

-Dash codes of P0602 (ECM/PCM Power Input Intermittent) and P2509 (Control Module Programming Error/Not Programmed) Probably based on hacked ECM.

-Truck starts, stops, runs fine. No obvious problems. No other lights on.

-Does not pull any which way when stopping.

-ABS data steam on the scanner shows a matching speeds between the front left, front right, and rear speed sensor, although it does show a speed of 3 MPH when at a complete stop. But since there is no ABS lights on, this does not concern me.

-Stumped Mechanic Here.


What I know of Brake Lights Only Being On:
-From my understanding and past experience, brake light onlys are on because of the emergency brake pedal depressed, low brake fluid, or loss of hydraulic pressure (air in line, broken line, bad caliper)

geohockey14

brake light will come on if there isnt enough tension on the cable dont no if this helps you or not good luck

Joey-D

But it is a solid brake light, not flashing. It would flash if it was the ebrake. Based on the dealer diagnosis, I need a new CAB module. CAB stands for Control Antilock Brake. I will get it late next week and hopefully it will fix it. Thanks though.

Hintonc393

Some where there is a switch called a differential pressure switch, on older GM trucks they had a lot of issues with it not resetting after the brakes were bled. That switch is in the system to turn on the brake failure light on if you have either the front or rear brake system flow more fluid than the other. Like in the case of a blown wheel cylinder or caliper. The small shuttle in the valve can stick in one position or the other causing the light to never go off. I am not sure where it is on that truck but it should have one.

Joey-D

I took it to the dealership hoping their starscan could dig a little deeper. They said the CAB module (Controller Antilock Brakes) is bad with an internal ground. They ordered the part last week and hopefully it will solve the problem. I should know in the next couple days.