Brake-Magnet Open and Short-Circuit Diagnosis
- Select the fault chart and circuit identified by the actuator code.
- Separate magnet, connector, ground, harness, and controller faults.
- Verify the indicated repair clears the actuator DTC.
- Digital multimeter — Measure magnet resistance and perform chart-directed continuity checks with the circuit isolated as directed.
- Electrical test leads and connector probes — Contact the specified terminals without spreading connector contacts or damaging seals.
- Inspection light — Inspect controller and wheel-end connectors, ground connections, and suspension-adjacent harness routing.
- Basic hand tools — Access connectors, disconnect the affected brake when directed, and correct accessible connection or mounting problems.
- Wire brush — Remove corrosion from accessible ground mating surfaces during an indicated ground repair.
Actuator faults identify a brake-magnet circuit and distinguish an open circuit, a short to battery, or a short to ground. Use the fault's axle and side designation to choose the affected circuit rather than inspecting an unrelated wheel end.
The charts begin with a power cycle and direct inspection of connectors, pins, grounds, and harness damage. Check both the controller end and affected wheel end, including places where suspension movement may pinch or cut the axle harness.
The open-circuit chart calls for checking the affected magnet's resistance and, with the axle harness disconnected from the controller, testing continuity between the corresponding brake pin and chassis ground. The supplied manual does not state a numerical magnet-resistance acceptance value.
When all actuators report shorts to battery, the chart specifically directs attention to the main chassis ground. For a short-to-ground investigation, the chart includes disconnecting the affected brake and rechecking for a short. Follow the resulting branch to harness correction, component replacement, or controller replacement, then verify fault status.
How It Works
Fault identity determines the test path
An actuator fault identifies a brake-magnet circuit and classifies the condition as an open, short to battery, or short to ground. Use its axle and side designation to select the affected circuit, then power-cycle and inspect as directed by the matching chart. A circuit fault does not by itself prove that the magnet or controller has failed.
Connection integrity and harness movement
An open interrupts the intended current path, while a short creates an unintended electrical path. Loose or corroded connections can restrict current, and suspension movement can chafe, pinch, or cut harness insulation and conductors. Inspect both the controller end and affected wheel end; when all actuators report shorts to battery, the chart specifically directs attention to the main chassis ground.
Isolation makes electrical tests meaningful
Disconnecting the axle harness from the controller establishes the configuration required for the chart's continuity checks; perform resistance and continuity measurements only on a de-energized circuit. The open-circuit chart includes magnet resistance testing, but the supplied manual gives no numerical acceptance value. For a short-to-ground fault, disconnect the affected brake and recheck when directed, then follow the resulting branch rather than assuming which component failed.
Step-by-Step Procedure
0/8 doneDiagnostic Chart
| Symptom | Check | Spec / Expected | Likely cause & fix |
|---|---|---|---|
| An actuator code reports an open circuit. | Identify the affected axle and side, power-cycle as directed, and inspect connections and harness condition. Check the affected magnet's resistance and, with the axle harness disconnected from the controller, test continuity between the corresponding brake pin and chassis ground. | The supplied manual does not state a numerical magnet-resistance acceptance value; interpret continuity results through the selected fault chart. | Possible interrupted magnet winding, disconnected or damaged terminal, ground-path defect, or broken harness conductor. Basis: Lippert-Anti-Lock-Braking-System |
| All actuators report shorts to battery. | Follow the selected chart and inspect the main chassis ground before condemning individual magnets or the controller. | The chart specifically directs attention to the main chassis ground for this fault pattern. | A main chassis ground defect may affect the shared electrical reference and produce a system-wide fault pattern. Basis: Lippert-Anti-Lock-Braking-System |
| An actuator code reports a short to ground. | Inspect the designated circuit at the controller, wheel end, and suspension-related pinch points. Disconnect the affected brake and recheck for the short when the chart directs. | Use the recheck result to follow the chart branch toward harness correction, component replacement, or controller replacement. | Possible grounded harness conductor or a fault in the affected brake circuit; isolation helps distinguish the fault location. Basis: Lippert-Anti-Lock-Braking-System |
| The actuator DTC remains active after a correction. | Confirm the repaired circuit matches the fault's axle and side, complete any required power cycle, and verify fault status. If active, continue the appropriate chart rather than replacing unrelated parts. | Repair verification requires the DTC to be inactive. | An unresolved circuit defect, an incorrect repair location, or an incomplete chart-directed verification sequence. Basis: Lippert-Anti-Lock-Braking-System |
At the Bay: Diagnose the Case
CASE 1 / 4
An actuator code reports an open circuit.
- Test
- Compare
- Correct
Select the next check
Basis: Lippert-Anti-Lock-Braking-System. A likely cause is a hypothesis; confirm it with the applicable service procedure before repair.
Common Bay Mistakes
- ✕ Inspecting an unrelated wheel end instead of the coded axle and side.
- ✕ Inventing a magnet-resistance acceptance value.
- ✕ Measuring resistance on an energized circuit or skipping required isolation.
- ✕ Replacing the controller before completing the fault-chart branches.
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: Shop Test Equipment
ABS Sensor Gap & Blink-Code Scanner
Non-magnetic feeler gauge, AC millivolt meter on the sensor, ECU blink-code button
🛠 Equip your bay for this test →Symptom: Post-repair verification.
Spec limits used
- 1.00–1.75 mm — Wheel-speed sensor air gap (Lippert ABS manual, p.13)
- 068Ah / 0006h — Sensor fault codes (Lippert ABS)
- illustrative only — Sensor AC output while spinning (General shop practice)
Simulated readings for practice. Always follow the manufacturer's procedure and values on a real trailer.
Source: Lippert-Anti-Lock-Braking-System — 7-9