We summarize the common failure modes of automotive connectors into six categories: contact-related, mechanical, environmental & corrosion, electrical, process/material, and assembly & application.
I. Contact Failures
1. Increased Contact Resistance (High Resistance)
- · Phenomenon: Signal packet loss, intermittent sensor malfunctions, lamp flickering, heat generation in power circuits; intermittent failure triggered by vibration.
- · Root Causes: Worn terminal plating, foreign contaminants on contact surfaces, corrosive film, incomplete mating, spring stress relaxation, poor terminal crimping.
- · Risk: Intermittent failures are the hardest to reproduce and account for most occasional after-sales defects.
2. Open Circuit (Complete Disconnection)
- · Phenomenon: Total loss of function.
- · Root Causes: Crimped wire breakage, fatigue fracture of terminal spring, terminal back-out, wire strand fatigue fracture at wire bend root.
- · Phenomenon: Fault occurs under vibration or temperature variation, and recovers at rest; diagnostic logs sporadic DTCs.
- · Root Causes: Insufficient spring clamping force, excessive terminal clearance, partially broken crimp, fretting corrosion.
3. Intermittent Open Circuit / Poor Contact
Fretting corrosion is the top chronic issue for automotive connectors: tiny reciprocating vibration damages plating and forms oxide powder, leading to sharp rise of contact resistance.
4. Short Circuit (Conduction between Adjacent Terminals)
- · Phenomenon: Fuse blown, module burnout, signal disorder; fire risk exists for high-voltage applications.
- · Root Causes: Metal debris, solder balls, plastic housing fragments, warped/deformed terminals, insufficient insulation creepage distance, conductive condensed moisture.
- · Phenomenon: Abnormal CAN/LIN signals and false messages.
5. Cross-Interference / Crosstalk (Signal Cross-Talk)
Root Causes: Deformed terminals, damaged insulation, conductive foreign matter bridging.
II. Mechanical Structure Failures (Housing, Terminal, Locking, Secondary Lock CPA/TPA)
1. Incomplete Connector Mating (Partial Mating)
- · Phenomenon: Not fully engaged visually; the latch appears hooked but not seated. Insufficient contact pressure, highly prone to fretting corrosion and heat generation.
- · Root Causes: Insufficient assembly force, foreign objects blocking the mating interface, deformed latch, wire harness tension. Partial mating is a frequent issue in vehicle assembly.
- · Phenomenon: The connector plug detaches under harness tension or vehicle vibration.
- · Root Causes: Insufficient latch wall thickness, material embrittlement (PBT hydrolysis), damage during assembly due to prying, over-travel pressing, molding defects (shrinkage voids, weld lines).
- · Phenomenon: Terminals can be pulled backward; terminal back-out occurs under driving vibration.
- · Root Causes: Missing TPA installation, TPA not pushed to fully locked position, fractured TPA latch.
- · Phenomenon: Terminals recede backward into the housing, failing to mate properly; intermittent open circuit.
- · Root Causes: Unlocked TPA, damaged terminal barbs, harness tension transferred directly to terminals, improper hard pulling of wires during maintenance.
- · Phenomenon: Progressive cracks on housing. PBT or nylon suffers Environmental Stress Cracking (ESC) when exposed to chemicals such as coolant, cleaning agents or hand creams.
- · Root Causes: Residual molding stress plus chemical exposure; over-tight assembly; low-temperature impact.
2. Main Latch Fracture / Disengagement
- · Phenomenon: The connector plug detaches under harness tension or vehicle vibration.
- · Root Causes: Insufficient latch wall thickness, material embrittlement (PBT hydrolysis), damage during assembly due to prying, over-travel pressing, molding defects (shrinkage voids, weld lines).
3. Secondary Lock CPA/TPA Failure (Unlocked, Fractured, Missing Installation)
- · Phenomenon: Terminals can be pulled backward; terminal back-out occurs under driving vibration.
- · Root Causes: Missing TPA installation, TPA not pushed to fully locked position, fractured TPA latch.
4. Terminal Back-out inside Housing (Terminal Rearward Movement)
- · Phenomenon: Terminals recede backward into the housing, failing to mate properly; intermittent open circuit.
- · Root Causes: Unlocked TPA, damaged terminal barbs, harness tension transferred directly to terminals, improper hard pulling of wires during maintenance.
5. Stress Cracking (Plastic Housing)
- · Phenomenon: Progressive cracks on housing. PBT or nylon suffers Environmental Stress Cracking (ESC) when exposed to chemicals such as coolant, cleaning agents or hand creams.
- · Root Causes: Residual molding stress plus chemical exposure; over-tight assembly; low-temperature impact.
III. Environmental and Corrosion Failures
1. Fretting Corrosion
Key point: It is not large-scale macro vibration, but micron-level tiny relative sliding motion that damages tin plating and forms high-resistance tin oxide powder. It can be triggered by temperature cycling and road vibration. This issue is most common in low-voltage connectors with tin plating. Gold plating can greatly mitigate this problem but comes with higher cost.
2. Electrochemical Corrosion / Moisture Corrosion
- · Phenomenon: White deposits or green rust on terminal surface; rising contact resistance.
- · Triggers: Moisture, salt spray (road de-icing salt), condensed water, accumulated water inside housing. Water vapor penetrates after seal failure; galvanic corrosion occurs when electrolyte exists (contact between dissimilar metals).
- · Phenomenon: Latch breaks easily upon slight impact.
- · Root Causes: Plastic pellets undergo hydrolysis under high temperature and high humidity, making material brittle. This risk is especially severe in the hot-humid environment of engine compartments.
3. Hydrolytic Aging (Plastic Material)
- · Phenomenon: Latch breaks easily upon slight impact.
- · Root Causes: Plastic pellets undergo hydrolysis under high temperature and high humidity, making material brittle. This risk is especially severe in the hot-humid environment of engine compartments.
4. Chemical Attack
Splashes of coolant, engine oil, brake fluid, cleaning agents or urea vapor on connectors lead to plastic housing cracking and swelling failure of rubber seals.
5. Mold & Dust Accumulation
Low risk in cabin interior. For connectors fitted on chassis or wheel arches, sediment and mud buildup damage sealing and create conductive bridges resulting in short circuits.
IV. Crimping Process Failures (Key Focus of Harness Maker PFMEA)
Crimping is a major source of connector failures. Crimp height measurement and cross-section metallographic analysis are the main verification methods.
1. Poor Conductor Crimping
- · Over-crimping: Copper strands are cut or develop microcracks, resulting in wire breakage after fatigue loading.
- · Under-crimping: Insufficient clamping force, high contact resistance and heat generation; wire can be pulled out easily.
- · Stray strands: Copper strands flare outward, creating risk of short circuit between adjacent terminals.
2. Poor Insulation Crimping (Bell Mouth)
Absence of bell mouth → sharp cutting edge damages wire insulation, leading to wire breakage after long-term bending; excessive bell mouth results in inadequate clamping force.
3. Crimp Position Offset, Insulation Jacket Crimped into Conductor Zone → High resistance and heat generation.
Other joining processes: Ultrasonic welding and brazing carry risks such as cold solder joints, solder wicking along insulation, and foreign matter of solder balls.
V. Electrical-Specific Failures (Including High Voltage HV Connectors)
Low Voltage
1. Overcurrent Heating & Terminal Thermal Creep When exceeding rated current, terminal springs undergo stress relaxation under heat → contact force further decreases → higher resistance, forming a vicious cycle. In severe cases, plastic housing gets scorched or melted.
2. Insulation Aging, Leakage Current & Creepage Contaminants plus moisture cause increased leakage current along the plastic housing surface.
Failures Unique to High-Voltage Connectors (New Energy)
1. Contact Overheating & Thermal Runaway: Under high current, minor poor contact will trigger significant temperature rise.
2. Electric Arc / Arcing: Arcs generate during live mating/unmating or contact separation and ablate terminals. HVIL interlock circuit is specially designed for prevention in HV systems.
3. Dielectric Breakdown & Partial Discharge (PD): Caused by insufficient insulation clearance, air bubbles or contamination; resulting in creepage and breakdown under high voltage.
4. HVIL Interlock Circuit Failure: Poor contact of interlock terminals triggers vehicle high-voltage fault, blocking high-voltage activation.
5. Aging of HV sealing gaskets. Ingress of moisture leads to surface discharge.
VI. Human / Maintenance-related Failures (Major Source of After-sales Cases)
1. Improper terminal removal tools used during maintenance, resulting in damage to terminal barbs, TPA and housing.
2. Sealing gasket misassembly or missing installation; paper scraps, sediment introduced during assembly.
3. Poor harness routing with excessive tension and bending, applying continuous external force on connectors.
4. Mismatched connectors forced together by brute force, causing permanent deformation of terminals and latches.
Post time: Oct-14-2026