BYD Dolphin Intermittent AC Charging Failure: Charge Port Temperature Sensor Drift Diagnosis and Repair

Fault Background

The Dolphin's AC charging path is short but involves many links: AC charging station → charging gun and AC/DC combo charge port → on-board charger (OBC) → traction battery. If any sensor on this path "misspeaks," charging will be halted. This article documents an intermittent no-charging case with no DTCs and seemingly normal live data—the real culprit is hidden inside the charge port: a temperature sensor with resistance drift.

Fault Symptom

Cause Analysis

1. AC charging station fault—station-side issue, verifiable by swapping stations.
2. OBC fault—OBC abnormality, but normal DC fast charging significantly reduces suspicion.
3. AC/DC combo charge port fault—internal wiring or sensor abnormality in the charge port.
4. Battery pack fault—battery refuses to charge.
5. Low-voltage electronic control fault—control system misjudgment.

Diagnostic Procedure

1. First visit: VDS scan shows no DTCs; available updates for OBC and DC-DC converter are performed, test drive after update is normal. Customer reports fault recurrence after a few days—update only "seemed to fix it."
2. Second visit: Connected to charging station, everything tests normal; instrument shows charging power 6.3 kW, data normal. Confirmed with customer that fault is intermittent, exact occurrence time cannot be pinpointed.
3. Extended live data observation: With gun plugged, continuously observe OBC and battery pack data—OBC system status normal, working status engaged, AC side voltage 216 V, AC side current 31.2 A, internal temperature 13 °C, charge port temperature 18 °C, fan duty cycle 0% (indicating no high temperature in battery pack or OBC).
4. Capturing the anomaly: After about 1 hour of charging, charge port temperature suddenly rises above 50 °C, while other internal temperatures are only slightly above 20 °C; continued observation shows this temperature fluctuating between 20 °C and 55 °C, while instrument charging power remains stable at ~6.3 kW—charge port "temperature" does not match reality.
5. Following the clue: Consult wiring diagram; charge port temperature sensor is located on AC/DC combo charge port. Disconnect sensor connector B53, pins 1 and 2 are sensor 1. Measured resistance 16.95 kΩ—resistance drifts slowly, suspected internal poor contact.
6. Three-way verification: With sensor disconnected, VDS live data shows charge port temperature 40 °C; with sensor shorted, shows maximum temperature. OBC responds correctly in both extreme states, indicating wiring and OBC are normal; issue is isolated to sensor itself.
7. Substitution verification: Replace sensor with a 16 kΩ resistor (slightly lower than measured resistance), live data temperature stable, charging returns to normal—confirming charge port internal sensor is faulty.
8. Final repair: Replace AC/DC combo charge port assembly, retest sensor resistance stable at 16.27 kΩ, long-duration charging normal, fault resolved.

Repair Plan

1. Perform two extreme tests—disconnect sensor connector and short the connector—to quickly determine if wiring and OBC are normal.
2. After confirming sensor failure, directly replace the AC/DC combo charge port assembly (sensor is integrated into charge port, not available separately).
3. After replacement, retest sensor resistance and observe charging live data to confirm temperature is stable and no longer fluctuating.
4. Recommend customer perform a full charging cycle verification (charge to set level) to confirm overnight charging no longer interrupts.

Key Parameter Quick Reference

Safety Warnings

• Involves AC charge port and OBC; must perform complete vehicle power-down and unplug charging gun before inspection.
• Shorting sensor is a temporary diagnostic measure; remove shorting wire before returning vehicle to customer, never deliver vehicle with short in place.
• After replacing charge port assembly, confirm charging gun inserts and locks smoothly to prevent gun detachment during charging.

Repair Insights

This case is most easily misled by "no DTCs + normal live data." Three lessons: First, look at live data more carefully—a single reading being normal doesn't mean it's always normal; long-term observation caught the 20–55 °C fluctuation. Second, use extreme method for reverse verification—disconnect and short the sensor, use OBC's response to prove wiring is fine, saving half the effort compared to direct part replacement. Third, substitution method for confirmation—a 16 kΩ resistor can make the fault "appear," small tool solves big judgment. The answer to intermittent faults often lies in those "seemingly normal" values.

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【This article is for reference only】