Use Breakaway Testing to Isolate Actuator Faults
- Distinguish actuator operation from confirmed pressure generation.
- Use breakaway results to isolate the likely fault area.
- Apply the documented voltage branches without inventing an equality rule.
- Wheel chocks — Secure the trailer against movement before testing.
- Digital multimeter — Perform the specified white-to-yellow voltage check after fully charging the breakaway battery.
- Battery charger — Fully charge the breakaway battery using a charger appropriate for the battery.
- Timer — Track switch-pulled duration during each outlined test step.
- Hydraulic brake pressure gauge — Verify pressure generation where the applicable actuator procedure provides for gauge testing; use compatible fittings and follow its connection instructions.
The breakaway test separates actuator operation from faults associated with the tow-vehicle controller or connecting wiring. It is a diagnostic test with a time limit, not an instruction to leave the emergency system energized. Dexter limits each outlined test step to no more than two minutes with the switch pulled; values vary by maker.
If the actuator runs and develops pressure during this test, the source treats the actuator as functioning properly. The likely fault is then the electronic controller or wiring between the tow vehicle and actuator. Hearing the actuator run alone does not establish the same result.
If the actuator runs but fails to build pressure, the source identifies a likely solenoid-valve fault and directs actuator replacement. If it does not run, fully charge the breakaway battery before continuing with the specified white-to-yellow voltage check.
Dexter specifies at least 12 volts for that check, identifies a reading below 12 volts with a switch or breakaway-wiring fault, and directs replacement when the reading is greater than 12 volts and the actuator still does not run. Values vary by maker. The supplied decision wording does not explicitly resolve an exactly-12-volt nonrunning result, so this lesson does not create an additional replacement rule.
How It Works
What the breakaway test isolates
The breakaway test separates actuator operation from faults associated with the tow-vehicle controller or connecting wiring. When the actuator both runs and develops pressure, the source treats it as functioning properly and directs attention toward the controller or connecting wiring. This result does not establish that every wheel-end brake component is operating correctly.
Sound is not hydraulic performance
An audible running actuator confirms activity, but it does not prove that hydraulic pressure is being generated. Pressure generation depends on hydraulic components directing and containing fluid, not merely on motor operation. For an actuator that runs without developing pressure, this source identifies a likely solenoid-valve fault and directs actuator replacement.
Time and voltage boundaries
Dexter limits each outlined test step with the switch pulled to 2 minutes; values vary by maker, so use the applicable procedure and restore the switch promptly after testing. For a nonrunning actuator, fully charge the breakaway battery before checking voltage between the white and yellow wires; the stated check is At least 12 V. The source distinguishes readings below and greater than the threshold but does not explicitly resolve an exactly-12-volt nonrunning result.
Step-by-Step Procedure
0/7 doneDexter breakaway-test values; values vary by maker
| Maximum time with switch pulled during each outlined test step | 2 minutes |
| White-to-yellow voltage check | At least 12 V |
| Stated low-voltage branch | Below 12 V: defective switch or breakaway wiring |
| Stated actuator-replacement branch | Greater than 12 V with actuator still not running |
Diagnostic Chart
| Symptom | Check | Spec / Expected | Likely cause & fix |
|---|---|---|---|
| Actuator runs and develops pressure during the breakaway test. | Confirm both running and pressure generation using the applicable procedure, then investigate the tow-vehicle electronic controller and wiring between the tow vehicle and actuator. | Maximum switch-pulled duration per outlined Dexter test step: 2 minutes; values vary by maker. | The source treats the actuator as functioning properly; the likely fault is the controller or connecting wiring. Basis: LDServiceOnline |
| Actuator runs but does not develop pressure. | Confirm the absence of pressure rather than relying on actuator sound, then follow this source's actuator-replacement direction. | Running without pressure generation is the stated likely solenoid-fault branch. | Likely solenoid-valve fault. Basis: LDServiceOnline |
| Actuator does not run and voltage is below the stated threshold. | Fully charge the breakaway battery before performing the specified white-to-yellow voltage check; inspect the switch and breakaway wiring when the low-voltage branch applies. | Below 12 V: defective switch or breakaway wiring | Defective breakaway switch or breakaway wiring. Basis: LDServiceOnline |
| Actuator remains nonrunning after the breakaway battery is fully charged. | Measure voltage between the white and yellow wires. Follow the replacement direction only when its stated branch applies; seek applicable service clarification for an exactly-12-volt result. | At least 12 V; replacement branch: Greater than 12 V with actuator still not running. | The source directs actuator replacement above the threshold; the equality case remains unresolved. Basis: LDServiceOnline |
At the Bay: Diagnose the Case
CASE 1 / 4
Actuator runs and develops pressure during the breakaway test.
- 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
- ✕ Treating actuator noise as proof of pressure generation.
- ✕ Leaving the breakaway switch pulled beyond the test limit.
- ✕ Condemning a nonrunning actuator before fully charging the breakaway battery.
- ✕ Applying Dexter values universally or inventing a replacement rule for the equality case.
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 — 31