Chang'an CS15EV On-Board Charger Fault Diagnosis and Disassembly/Assembly Guide

Fault Background

The on-board charger (OBC) of the Chang'an CS15EV (B311-EV project, 775 manual) uses an interleaved PFC + full-bridge isolated conversion topology: AC input first passes through the Inrush current limiting circuit (composed of thermistor and resistor, suppressing inrush current at power-on), then through EMI filtering into the continuous interleaved PFC, followed by the full-bridge isolated conversion circuit to output high-voltage DC; a DSP master control chip coordinates PFC, full-bridge isolated conversion, and current control, while the auxiliary power supply powers the primary-side control IC, drive circuit, and CAN communication circuit; CAN data communication with the BMS is via isolated optocouplers, and a battery detection circuit detects whether the battery on the high-voltage output side is properly connected to prevent charger faults. The manual lists 21 DTCs (P1A80~P1A92 + U12B0~U12B2) and a standard "retest → determine boundary → replace unit" handling method. This article is organized as a diagnostic and disassembly/assembly guide.

Connector and Torque Specifications

Low-voltage connector: control pilot CP, indicator output LED×2 (+12V/50mA), low-voltage input positive KL30 (+12V/1A), hard-wire wake-up output HW_WAKEUP, CAN high HS_CAN_H, indicator output ground LED_GND, low-voltage input negative KL31_GND. High-voltage DC output terminals are divided into positive/negative poles (B terminal is negative).

Torque specifications: Charger upper cover mounting bolts (No. 3 star hex) ×11; charger lower cover mounting bolts (No. 3 star hex) ×23 — the upper cover is only allowed to be removed by professional personnel.

DTC Quick Reference (P1A8x / U12Bx)

Unified handling mode: Correctly connect the slow charging device and recharge → use the diagnostic scan tool to enter the VCU to clear history DTCs → read current DTCs → determine boundary according to the table.

Key points: P1A89/P1A8A look at the battery-side voltage window (430V/220V), P1A8B/P1A8C look at the grid-side window (80VAC/273VAC), P1A90/P1A91 look at charging current 12A — outside the window, replace the charger; inside the window, first check the corresponding external system, then clear code and retest.

Disassembly/Assembly Procedure (7 Steps)

Safety prerequisites: ① Cut off high voltage; ② Ensure the charging gun is not connected; ③ Turn the key to OFF and remove the service disconnect switch before operation. When removing the charger, remove the charger bracket assembly first.

1. With no charging gun connected, turn the key to OFF, cut off high-voltage power, and remove the charger assembly connector;
2. Remove the charger water hoses and drain the coolant;
3. Remove the PTC water hoses and connector;
4. Use a torque wrench to remove the charger bracket assembly (take it off the mounting bracket);
5. Use a torque wrench to remove the charger assembly;
6. For installation, reverse the order;
7. After all installation is complete, bleed the system and add coolant.

Special tools: Diagnostic scan tool (to collect dynamic system operating data), digital multimeter (voltage/resistance/current characteristic parameters), insulating gloves, megohmmeter (to measure insulation resistance of electrical equipment), torque wrench.

Safety Warnings

• This article is for technical reference. Charger disassembly/assembly involves high voltage and coolant, and must be performed by qualified professional technicians (with electrician certification + company training authorization) according to OEM specifications.
• All three prerequisites are indispensable: cut off high voltage, charging gun not connected, key OFF + remove service disconnect switch; after reassembly, bleed the system and add coolant to prevent water pump cavitation and localized overheating.
• The upper cover bolts (11) and lower cover bolts (23) are No. 3 star hex, tighten to specified torque to ensure assembly reliability; non-professionals are not allowed to remove the charger upper cover.
• When measuring grid voltage, pay attention to live-work protection; check insulating gloves for leaks before use.

Maintenance Insights

The CS15EV OBC DTC table clearly states "who is responsible": of the 21 codes, 14 are "retest still reports → replace charger directly" (internal SCI/CAN/boost/self-check types), and only 7 require external troubleshooting — two battery voltage window codes (430V/220V), two grid window codes (80VAC/273VAC), one 12A overload code, and two temperature codes. During maintenance, first memorize the three sets of boundary values: 430±10V, 220±4V, 12A; outside the window, decisively replace the unit; inside the window, first check the battery/grid/wiring harness, and finally fall back to the "clear code and retest still reports → replace charger" logic. The troubleshooting chain for temperature code P1A8E is worth remembering: coolant level → water pump → live data reasonableness; if the order is wrong, a water pump fault can be misdiagnosed as a charger fault. Finally, the three safety prerequisites for disassembly/assembly, among which "remove the service disconnect switch" is most easily overlooked — it is the true power cutoff point for high-voltage maintenance.

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【This article is for reference only】