Diagnose Slow Response and a Nonrunning Actuator
- Separate slow response, no actuator operation, and excessive braking.
- Verify hydraulic bleeding, wiring capacity, supply voltage, and grounding.
- Use controller adjustment and breakaway testing in the correct diagnostic path.
- Digital multimeter — Measure supply voltage between the actuator black and white wires under the specified test conditions.
- Tape measure — Check the distance between the tow vehicle and actuator when evaluating wire-size recommendations.
- Brake bleeder wrench — Open and close bleeders during the applicable actuator and trailer-brake bleeding procedure.
- Clear bleeder hose and catch container — Collect discharged fluid and observe escaping air during bleeding.
- Wire brush — Clean accessible ground-contact surfaces when correcting a poor ground connection.
- Basic hand tools — Access wiring connections and secure ground hardware according to the applicable instructions.
Slow brake response does not by itself establish actuator failure. The source begins with re-bleeding the trailer brakes and actuator, then considers wiring size and controller adjustment. Its running-clearance adjustment instruction applies to drum brakes, not to the disc calipers covered in this module.
Power and ground wire recommendations depend on the distance between the tow vehicle and actuator. Dexter specifies 12-gauge black and white wires for distances under 10 feet and 10-gauge wires for distances over 10 feet, with other wires at least 16 gauge. Values vary by maker; the supplied wording does not assign the exactly-10-foot case.
For an actuator that does not run with the ignition on and brake pedal depressed, compare the installation with the applicable electrical schematic. The separate supply-voltage check is performed with the ignition on and brakes not applied. Dexter specifies 12–13 volts between the actuator black and white wires for that check; values vary by maker.
The no-run sequence also calls for correcting the ground connection and testing operation through the breakaway procedure. Controller adjustment remains a separate diagnostic path: the source permits a more aggressive inertia-sensor setting or increased gain for slow response, while excessive braking calls for reduced gain. Follow the controller's applicable instructions rather than treating gain as a repair for every fault.
How It Works
Slow response is a symptom, not an actuator verdict
Air compresses under hydraulic pressure, delaying pressure buildup at the calipers, so the source begins slow-response diagnosis by re-bleeding the actuator and trailer brakes. If response remains slow, evaluate wiring capacity and controller adjustment rather than immediately replacing the actuator. The source's running-clearance adjustment instruction is for drum brakes, not these disc calipers.
Supply and ground form the operating circuit
Resistance in undersized wiring or poor connections can reduce the electrical power available to the actuator during operation. Dexter recommends 12 gauge black and white wires for distances under 10 feet, 10 gauge for distances over 10 feet, and other wires of at least 16 gauge. These recommendations vary by maker, and the supplied wording does not resolve exactly 10 feet.
Test conditions determine what a result means
The no-run complaint is observed with the ignition on and brake pedal depressed, but the separate Dexter supply check requires the ignition on and brakes not applied, with 12–13 V between black and white wires. A satisfactory released-brake reading does not by itself prove that the circuit will maintain supply during operation, because connection resistance can become more evident under load. Controller adjustment is a separate path: follow its applicable instructions for a more aggressive inertia-sensor setting or increased gain when response is slow, and reduced gain when braking is excessive.
Step-by-Step Procedure
0/7 doneDexter actuator diagnostic values; values vary by maker
| Black and white wires: actuator less than 10 feet from tow vehicle | 12 gauge |
| Black and white wires: actuator more than 10 feet from tow vehicle | 10 gauge |
| Other actuator wires | Minimum 16 gauge |
| Black-to-white voltage: ignition on, brakes not applied | 12–13 V |
Diagnostic Chart
| Symptom | Check | Spec / Expected | Likely cause & fix |
|---|---|---|---|
| Brakes respond slowly. | Re-bleed the actuator and trailer brakes using the applicable actuation-system procedure, then reassess response. | Use the applicable bleeding procedure; do not apply the source's drum running-clearance adjustment to disc calipers. | Trapped air can absorb hydraulic displacement before useful caliper pressure develops. Basis: LDServiceOnline |
| Slow response persists after bleeding. | Compare the black and white wire sizes with the tow-vehicle-to-actuator distance, and verify the remaining actuator wiring. | Dexter: under 10 feet, 12 gauge black and white wires; over 10 feet, 10 gauge; other wires, Minimum 16 gauge. Exactly 10 feet is not assigned; values vary by maker. | Inadequate wire capacity can contribute to voltage loss and poor actuator response. Basis: LDServiceOnline |
| Actuator does not run with ignition on and brake pedal depressed. | Compare installation wiring with the applicable schematic. For the separate supply check, release the brakes and leave ignition on; measure between black and white wires, correct the ground connection as directed, and continue with the documented breakaway procedure if operation is still absent. | Dexter supply check: 12–13 V between actuator black and white wires with ignition on and brakes not applied; values vary by maker. | Incorrect wiring, unsuitable supply voltage, or a poor ground may prevent actuator operation. Basis: LDServiceOnline |
| Response remains slow after preceding checks, or braking is excessive. | Review controller setup and adjust only through the controller's applicable instructions. | Slow response: more aggressive inertia-sensor setting or increased gain as permitted. Excessive braking: reduced gain. | Controller adjustment may not match the braking demand; gain changes do not repair hydraulic or electrical faults. Basis: LDServiceOnline |
At the Bay: Diagnose the Case
CASE 1 / 4
Brakes respond slowly.
- Test
- Compare
- Correct
Select the next check
Basis: LDServiceOnline. A likely cause is a hypothesis; confirm it with the applicable service procedure before repair.
Common Bay Mistakes
- ✕ Condemning the actuator from slow response alone.
- ✕ Inventing the exactly 10 feet boundary or substituting a drum-magnet wiring chart.
- ✕ Applying drum running-clearance instructions to disc calipers.
- ✕ Confusing the brake-applied complaint with the brake-released voltage check, or masking faults with gain.
Quick Check
Practice only — not scored.
Plan the Service Sequence
Planning practice only. Follow the applicable manufacturer's instructions, employer safety program and qualified supervision on real equipment.
Plan the first action. Compare the service steps with the bay mistakes.
Hands-on: Test Bench Practice
Symptom: Healthy trailer. Learn what good readings look like.
Tap a point to place the red probe.
Good system: ~12.6 V at pins, 3.2 Ω across a 12×2-inch magnet (unplugged), 3.0 A per magnet at 12 V full gain, and at least 10.5 V at the magnet — the chart values from the axle manuals.
Hands-on: Shop Test Equipment
Hydraulic Pressure & Relief Gauge
0–5,000 psi gauge on the pump pressure port, DC clamp meter, battery voltmeter
🛠 Equip your bay for this test →Symptom: Routine check before a customer pickup.
Spec limits used
- 3,200 psi — Primary relief (factory preset) (KTI Hydraulics Troubleshooting Manual 2019)
- 1,500 psi — Secondary relief, circuit 111 (KTI Hydraulics Troubleshooting Manual 2019)
- below 9 V — Low-voltage alarm (KTI remote)
- illustrative only — Motor current & voltage drop (General shop practice)
Simulated readings for practice. Always follow the manufacturer's procedure and values on a real trailer.
Source: LDServiceOnline — 29-31