Trailer Brakes Will Not Lock Up with Primus IQ Brake Controller # TK90160 in 2007 Silverado 1500  

Question:

Expert Reply:

The fact that your trailer brakes will not lock up at 20-25 mph speed does not necessarily indicate a problem with the brake controller. The best way to isolate the problem is to apply a circuit tester to the wires leading into one of the trailer electric brake assemblies to read the voltage reaching the brake.

You can use a voltage tester like # PT89ZR to read the voltage being delivered to the brake assembly. You should read +12 volts or very close to it at each brake when the controller gain is turned up and the manual override is engaged. If you do detect this voltage then the issue may be that the trailer brakes require adjustment, have worn or damaged brake magnets or require new brake pads. The linked articles detail several tests that can be done on electric brakes, and individual brake magnets, with a multimeter like # BTMT15 and circuit tester like # PTW2991.

If you do not detect the +12V signal at the brake assemblies you can disconnect the trailer and test the 7-way connector on the Silverado. You will need a helper on hand to operate the brake controller manual override while you apply the tester to the appropriate pins on the 7-way. If you refer to the linked photo of a vehicle-side 7-way you will see the two labelled pins where the tester should be applied. Ground the tester to the pin at 7-o-clock and apply the probe to the pin at 5-o-clock. You should detect +12V or close to it at the vehicle 7-way when the gain is turned up and the manual override is engaged.

If you do then you know the issue is on the trailer side. Inspect the trailer-side connector and the wiring for the brake circuit for any signs of corrosion or worn/damaged insulation. Repair or replace the damaged wiring or connector as needed.

If you do not detect +12V or close to it at the vehicle connector then the problem is in the vehicle 7-way connector, the vehicle wiring or the brake controller itself. Inspect the contacts on the 7-way for any signs of even slight green or white corrosion. You do not have to see rusted or crusty contacts to have a corrosion problem; even slight discoloration can indicate a problem and in this case the connector should be replaced. You can also inspect the vehicle wiring to the 7-way for any signs of worn or cracked insulation that could be causing a short on the brake output circuit before it reaches the 7-way.

If you happen to have a spare 12V battery you can apply power directly to the trailer connector to test brake function. Apply the wire from the battery negative terminal to the ground pin on your trailer connector and the wire from the positive terminal to the pin for the brake circuit; if you can get the trailer brakes to lock up when fed a direct 12V signal then you know the problem is upstream of the brakes.

Last you can test the output of the controller at the wiring at the back of the unit. Apply the circuit test probe for the grounded tester to the blue wire exiting the back of the controller. With the manual override engaged you should detect a nearly +12V signal on the blue wire; if so, you will then know that the controller is working and that the problem is somewhere down stream of the Primus IQ.

expert reply by: Adam R

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