Changan CS15EV Traction Battery Fault Diagnosis and Removal/Installation Guide
Fault Background
The traction battery of the Changan CS15EV (B311-EV project, 775 manual) is a ternary lithium-ion assembly: 168 cells (nominal 3.65V) configured as 2 parallel and 84 series, nominal voltage 307V, rated capacity 140Ah, providing energy to the motor and DC/DC converter. BCU (Battery Control Unit) collects and monitors voltage/current/temperature in real time, estimates SOC and available power, executes overvoltage/overcurrent/overtemperature alerts and leakage current protection, and includes CAN fault diagnosis and calibration. Fault codes are grouped into three major families: P1B/P1D/U12, covering insulation, interlock, relay drive, voltage/current/temperature, and CAN message timeout. Each code is paired with a "segmented measurement + part replacement as fallback" troubleshooting path. This article is organized into a diagnostic and removal/installation guide following the sequence: "insulation → interlock/relay → voltage/current/temperature → CAN/precharge".
Assembly Specifications and Interfaces
- Cell/pack configuration: 168 cells, 2 parallel and 84 series (2P84S), cell nominal 3.65V → total nominal 307V, rated 140Ah;
- High-voltage connectors: one each for main output (to PEU), slow charge (charging input harness assembly), and fast charge (safety switch plug assembly 2101335-AM50); interface definitions are all "left negative, right positive";
- Low-voltage connector: signal acquisition harness assembly I connects to vehicle low voltage (part number 1-1564526-1/TYCO, 18-pin) — pin6 = high-voltage interlock input HV_INTERLOCK_N, pin8 = DC charging CAN high, pin9 = DC charging CAN low;
- BMS architecture: main board ST1 24-pin / ST2 8-pin / ST3 16-pin / ST4 12-pin / ST5 8-pin + sub-boards 1#/2#/3# (each 8-pin + 28-pin ×3, responsible for sampling 84 series cells and temperature).
Insulation Fault Special Topic
P1B41 Insulation fault / P1D23 Insulation detection module fault (if the latter still appears after clearing codes and re-testing → replace BCU):
- Segmented localization: Sequentially disconnect the high-voltage connectors to OBC / PEU / fast charge, and use an insulation tester to measure the insulation resistance of the positive and negative lines to ground on both the "harness side" and "battery pack side" — <100MΩ is abnormal: if the harness side is abnormal, check the corresponding high-voltage components and harness insulation; if the battery pack side is abnormal, proceed to the next step;
- Freeze frame criteria: Read the insulation resistance at the time of fault; if less than 500Ω/V → replace the battery management controller assembly;
- In-box port-by-port criteria: Use an insulation tester to measure the insulation resistance between each high-voltage output port terminal and the box body — for the IPU port ≥500MΩ, for the charger port / fast charge port / safety maintenance switch terminal ≥200MΩ; if not met, replace the corresponding connector and the internal high-voltage electrical box connection busbar/harness;
- Finally, check whether the battery has water ingress, whether the busbar is worn, and whether high-voltage components are securely fastened.
High-Voltage Interlock and Relay Code Family
Interlock three codes: P1B4E Internal interlock loop open circuit (low-voltage plug pin6 backed-out terminal → each high-voltage connector interlock pin → base interlock pin backed-out → after opening the pack, short the interlock loop and measure continuity of main board ST3 pins 13#/14# → measure continuity to ground → replace BCU); P1B4F Short to VCC / P1B50 Short to GND (measure continuity of interlock loop to 12V power positive / to ground → replace faulty harness, otherwise replace BCU).
Relay drive code family (all follow the same path: disconnect the corresponding relay low-voltage control connector, use a multimeter to measure whether the corresponding pin on main board ST1 and the relay control connector pin are open / shorted to GND / shorted to VCC → replace harness / replace main board): High-side drive control terminal 1 (P1B92/93/94), main positive relay low-side (P1B60/61/62), main negative relay low-side (P1B63/64/65), precharge relay low-side (P1B66/67/68), DC charging relay low-side (P1B7C/7D/7F).
Mechanical end normally closed: P1B30 Main positive relay / P1B49 DC charging relay — use a multimeter to measure whether the relay is conductive: if conductive, replace the relay; if not, replace the main board.
Self-check: P1B54 Self-check failed — check the three high-voltage output ports and the safety maintenance switch for short/open circuit; if abnormal, replace the faulty component; if normal, check the internal high-voltage acquisition harness for short/open circuit; finally replace the BCU.
Voltage / Current / Temperature Codes
| Fault Code | Criteria | Action | ||
|---|---|---|---|---|
| P1B23 Total voltage too high level 4 | Total voltage ≥362V, highest cell >4.2V, maximum allowable charging current 0A | First check if the vehicle is still charging; otherwise replace BCU; if acquisition harness loose, reconnect | ||
| P1B02 Total voltage too high level 3 | Total voltage ≥360V, highest cell >4.2V | Same as above | ||
| P1B24 Total voltage too low level 4 | Total voltage ≤213V, lowest cell <2.5V, maximum discharge current 0A | Use Zhou Ligong CAN card to verify cell voltage sum → replace faulty cell; otherwise check acquisition harness/replace BCU | ||
| P1B05 Total voltage too low level 3 | Total voltage ≤221V, lowest cell <2.5V | Same as above | ||
| P1B25/P1B2D Cell voltage too high level 4/5 | Faulty cell measured ≥4.25V | If measured at module end → replace cell or module; if measured at sub-board sampling harness end → replace sampling harness; if not measurable → replace corresponding sub-board | ||
| P1B0B Cell voltage too low level 4 | Faulty cell measured ≤2.5V | Same three-way method as above | ||
| P1B21/P1B27 Charge current too high | Total current absolute value >20A, or >Ic+20 and lasting 2s; verification: battery total current − | motor current − DCDC current | ≥2A | Replace BCU and current sensor assembly |
| P1B22 Discharge current too high | >Id+20 and lasting 2s (Id determined by temperature/SOC from fault threshold table) | Replace BCU and current sensor assembly | ||
| P1B29 Module temperature too high | Highest temperature ≥57℃ and lasting 5s; after resting 0.5h, a module is still 2℃ higher than others | If sub-board collected temperatures are all ≥57℃ → replace sub-board; otherwise replace module acquisition harness assembly | ||
| P1D60/P1DB7 Cell voltage balancing failure | Still appears after re-test | Replace the sub-board corresponding to the faulty cell | ||
| P1D01 Total current acquisition rationality | Still appears after re-test | Replace main board and current sensor | ||
| P1B7F/P1B82 Total current sensor channel 1 short to GND/to VCC | Measure main board ST2 pin5 continuity to chassis ground/12V | If conductive or signal line open → replace harness; otherwise replace main board |
CAN and Precharge / Heating Special Topics
CAN family (U1200 Vehicle CAN → refer to P1DEE VCU CRC; U1202 Internal CAN → refer to P1DF0 CMU CRC; U1204 AC charging CAN → refer to P1DEF OBC CRC): Communication harness backed-out terminal → replace harness; replace VCU / replace AC charger; if still reported → replace BCU (for internal CAN type, replace BCU or battery state manager assembly).
P1D30~P1D36 Charger message timeout family (identification/data sync/charge ready/charge status/abort/statistics): 120±10Ω three-segment localization — measure the resistance of the vehicle DC charge port S+/S- → measure battery end 18-pin Pin8/Pin17 → measure main board ST3 Pin9/Pin10, determine segment by segment and replace the vehicle DC charging harness assembly / battery pack low-voltage harness / main board accordingly.
Precharge and heating: P1B44 Precharge failure — if high-voltage electrical box busbar is loose, tighten to torque or replace busbar; precharge resistor 52±5Ω; disconnect main board ST4/ST5, measure continuity of main negative relay and ST5 Pin3, main positive relay outer side and ST4 Pin5 → replace main board/replace harness. P1B87/88/89 Heating circuit open/overcurrent/heating relay normally closed — use multimeter to measure both high-voltage sides of the heating relay: if conductive, replace heating relay; otherwise replace main board and current sensor.
Post-Repair Three Checks and Removal/Installation Safety
Post-repair checks: ①Use battery offline test equipment (or CANalyzer monitoring) to confirm no BMS faults are reported; ②Use a dedicated air-tightness test fixture to seal high/low voltage connectors + air-tightness tester to test; if not passed, notify professional technical personnel; ③After vehicle restoration, use diagnostic scan tool to clear codes, re-power and read codes; if no faults, recovery is complete.
Removal/installation safety 10 items (excerpt): Operators must be trained in safe removal/installation and pass tests; environment dry and clean, equipped with dry powder fire extinguisher/fire sand, workbench insulated; lifting equipment fault-free and operated by professionals; disconnect safety switch before removal (located under front passenger seat); throughout, use insulated gloves, no metal objects, no water traces; no two or more people should remove/install simultaneously, and another person must accompany for emergency; special tools wrapped with insulating tape; parts/tools must not be placed on the battery assembly; exposed busbars and removed modules/cells/busbars must be immediately insulated with insulating tape, and small parts must not fall into the battery assembly.
Removal key points: First disconnect safety switch under front passenger seat → lift + hydraulic cart (near battery rear, left-right symmetrical) → disconnect front and rear connectors → first fully loosen then remove front and rear 4 bolts, then remove left and right sides (M12 + air wrench); top cover 40 fixing bolts + 2 limit nuts + 6 safety switch fixing bolts (one-time use); high-voltage electrical box top cover 4/3 mounting nuts; bolts connecting busbar and module must not be reused after removal; modules as components must not be disassembled as a whole; reassembly in reverse order.
Safety Warnings
- This article is for technical reference. Traction battery service is high-voltage work and must be performed by qualified technicians (electrician certificate + company training authorization) according to OEM specifications; before work, disconnect the safety switch and confirm no residual voltage on the bus.
- Insulation testing (100MΩ/200MΩ/500MΩ/500Ω/V criteria) uses an insulation tester, with insulated gloves throughout; removed modules/cells/busbars must be immediately wrapped with insulating tape.
- If air-tightness test fails, installation is strictly prohibited; the service environment must be equipped with dry powder fire extinguisher and fire sand; no more than two people should remove/install simultaneously.
Maintenance Insights
The most distinctive feature of the CS15EV traction battery code table is "segmented measurement + part replacement as fallback"; almost every code can be drawn as a binary localization tree: for insulation faults, disconnect and measure resistance at "OBC/PEU/fast charge three-segment harness + three high-voltage output ports + safety switch" point by point, 100MΩ determines harness side, 500Ω/V determines BCU side, 200MΩ/500MΩ determines in-box busbar — responsibility boundaries are clear enough to avoid disputes. The three interlock codes (open/short to VCC/short to GND) share the same "backed-out pin → continuity → replace BCU" path; the relay code family even numbers the high-side and low-side drive terminals for main positive/main negative/precharge/DC charging one by one (P1B60~68, P1B7C~7F), and with the mechanical end normally closed codes (P1B30/49) completely separates "drive circuit fault" from "contact sticking" — the former replaces harness/main board, the latter replaces relay. For voltage codes, remember four sets of numbers: 362/360V too high, 213/221V too low, 4.2/4.25V cell, 2.5V cell; for current codes, remember Ic+20/Id+20 lasting 2s and ≥2A verification formula; for temperature codes, remember 57℃/5s + 0.5h rest difference 2℃. Finally, don't forget the three post-repair gates: CANalyzer no faults → air-tightness pass → clear codes and re-read, missing any one means the repair is not complete.
【This article is for reference only】
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⚠️ High-voltage repairs require professional certification; this article is for technical reference only — always follow the OEM service manual.