bF Error Code on Hayes Genesis Brake Controller Used with Hydrastar Actuator on Mercedes ML Class


Hi etrailer I just had a Hayes 81790 installed in my w166 Merc ML, I plug this into the trailer which has a brand new Hydrostar hba 12 1200psi. I was using a red arc tow pro elite previously which operated the hydrastar but for some reason destroyed the trailer loom. Merc installed a new trailer working loom uninstalled the red arc and installed the MB approved Hayes Ive done research and know the hydrastar is compatible with the Hayes and I know the Hydastar unit is all good. In the car I keep getting the bF error. Are there some tests I can do at home or am I going back to the Merc dealership to evaluate?


Expert Reply:

On the Hayes Genesis brake controller # HA81790 the bF error indicates that there is power on the blue wire when there shouldn't be. This could be the result of the blue wire being connected in the wrong place, a short, or, if you have a breakaway system the pin might be pulled out.

It could also have to do with the connection of the brake controller red wire. On Mercedes vehicles the stop light switch wire that you would need is difficult to access so it is possible that the red wire was connected to the wrong wire on the vehicle. Check to see if there is constant voltage on the brake controller red wire using a circuit tester such as # 40376 or a meter if you have one.

Also inspect the vehicle and trailer side connectors and make sure they are clean and free of corrosion inside and out. There are some additional tests you can do.

In the truck cab you will need to sever the blue wire several inches from the back of the controller. Then use a circuit tester such as # 3808 to test the end of the blue wire coming out of the controller. It should only have power when you apply the manual override. If it shows power at idle then there is something wrong with the controller and it will need to be replaced.

If it tests fine then reconnect the blue wire. You can test the brake output pin on the vehicle side connector and it should only show power with the manual override. If it shows power any other time then there is a short somewhere between the connector and the brake controller you will need to track down.

If the truck side checks out fine then it could be the wiring for the Hydrastar actuator. Inspect the wires and look for pinched, frayed, or damaged wires and fix as needed. Make sure the ground wires are attached to clean and corrosion free bare metal surfaces.

I have also included some help articles on testing and troubleshooting brake controllers for you.

expert reply by:
Michael H

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