Primus Brake Controller Shows o9 Error Trailer Connected, Loss of Controller Ground

Updated 08/07/2018 | Published 08/05/2018

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Question:

getting a flashing error code 09 trailer connected unit losing ground, how can I correct the problem?

asked by: Gary S

Expert Reply:

Like you said, the 09 error code on the Primus brake controller # TK90160 indicates that a trailer is connected but the ground connection for the controller is lost.

On a brake controller, the best ground location would be the negative battery terminal if the controller is hardwired in. Really no other ground location is sufficient. This could also be a combination of more than one problem.

Once you have a secure ground check the trailer connector on the truck for dirt and corrosion at the pins and the back of the connector where the wires attach. There could be a short to the brake output pin that makes the controller think there is a trailer attached.

To test the controller itself you will want to sever the blue wire a few inches back from the controller leaving enough space to re-attach if the controller is fine. Then use a circuit tester like # PTW2993 if needed to test the end of the blue wire coming out of the brake controller. It should only show power when you apply the manual override. If it shows power at any other time, then that indicates a problem inside the controller, and it will need to be replaced.

I have also included a link to a brake controller troubleshooting FAQ that should help.

expert reply by: Michael H