Changan Eado EV Traction Battery Fault Inspection and Confirmation Guide

Fault Background

For the Changan Eado EV traction battery, fault inspection and confirmation starts with reading stored DTCs from the VCU via the diagnostic scan tool, then branches by code family: insulation family (P1B41/P1D23), interlock family (P1B4E/P1B4F/P1B50/P1B54), CAN family (U1200/U1202/U1204 and CRC/Counter sub-codes), total voltage family (P1B23/P1B02/P1B24/P1B05), cell voltage family (P1B2D/P1B25). Threshold values appear in pairs: total voltage too high level 4 ≥362V / level 3 ≥360V, too low level 4 ≤213V / level 3 ≤221V; cell >4.2V or <2.5V; insulation ≥500Ω/V, service disconnect switch to case ≥200MΩ. Each troubleshooting tree includes dual confirmation via "freeze frame + current value" and ends with replacing the battery management controller assembly. This article is compiled as a maintenance guide.

Insulation Fault Family

P1B41 Insulation Fault troubleshooting tree (segmented localization method):

1. High-voltage harness end: Use an insulation tester to measure the insulation resistance between the positive and negative lines and ground at the high-voltage harness connector—if abnormal, check OBC and connected high-voltage harness insulation / PEU (IPU) and connected high-voltage harness insulation / fast-charge high-voltage harness (measure the corresponding branch; if abnormal, replace the corresponding high-voltage harness);
2. Battery pack end: Measure the insulation resistance between the positive and negative lines and ground at the battery pack connector—if abnormal, proceed to the battery assembly side inspection;
3. Freeze frame: With the key in ON position, read the current DTC → tap the snowflake icon in the history DTC screen to read freeze frame data → read the traction battery insulation resistance at the time of fault (≥500Ω/V is normal);
4. Output port segment-by-segment: Use an insulation tester to measure the insulation resistance between the terminals of the battery assembly high-voltage output ports (connected to IPU / charger / fast charge) and the case—if abnormal, replace the corresponding high-voltage output port connector and harness;
5. Service disconnect switch: Measure whether the insulation resistance between the service disconnect switch terminal and the case is ≥200MΩ;
6. Visual inspection: Check whether the battery has water ingress or the copper busbar is worn through;
7. If still abnormal → replace the battery management controller assembly.

P1D23 Insulation Detection Module Fault: Clear DTCs with the diagnostic scan tool and re-read—if it reproduces, replace the battery management controller assembly; if it clears, clear DTCs and end the repair.

Interlock and Self-Check Fault Family

• P1B4E Battery Internal High-Voltage Interlock Loop Open: Check whether all high-voltage connectors (including the service disconnect switch) are securely connected → check the bases of high-voltage connectors on the traction battery assembly end → replace the high-voltage harness containing the abnormal connector / replace the battery management controller assembly;
• P1B4F High-Voltage Interlock Loop Short to 12V: Use the diagnostic scan tool to read the current DTC to confirm → use a multimeter to check continuity between the interlock loop and the 12V power positive → replace the faulty harness → replace the battery management controller assembly;
• P1B50 High-Voltage Interlock Loop Short to GND: Use a multimeter to check continuity between the interlock loop and body ground → replace the faulty harness → replace the battery management controller assembly;
• P1B54 Self-Check Failed: Remove the traction battery assembly → check the condition of connectors such as the battery assembly high-voltage output port (connected to IPU) → check whether the internal high-voltage acquisition harness of the battery assembly is damaged or loose → replace the faulty component/harness → replace the battery management controller assembly.

CAN Communication Fault Family

Total Voltage Fault Family

Total voltage acquisition harness check: Visually inspect and touch the acquisition harness connector to feel if it is loose → replace or reconnect the connector reliably → use a multimeter to check the total voltage acquisition harness circuit → replace the acquisition harness → replace the battery management controller assembly.

Cell Voltage Fault Family

P1B25 Cell voltage too high level 4 (see P1B2D for level 5): Use the diagnostic scan tool to read the current DTC, read the highest and lowest cell numbers → measure the actual voltage of the faulty cell from the module connector → if abnormal, replace the corresponding cell or module → then measure the faulty cell voltage from the cell board voltage acquisition harness end (to distinguish between cell fault and sampling harness fault) → based on the result, replace the cell/harness/battery management controller.

Key Parameter Quick Reference

Safety Warnings

• This article is for technical reference only. The traction battery is a high-voltage component; repairs must be performed by technicians trained in high-voltage procedures; disconnect high voltage and verify voltage before measurement.
• Insulation testing must be performed after disconnecting high voltage and removing the service disconnect switch; use the insulation tester and insulating gloves according to regulations.
• Cell replacement must be performed by professional battery repair organizations; do not disassemble modules while energized.
• Freeze frame data (snowflake icon) is the basis for distinguishing "historical intermittent" from "actual fault"; do not replace parts directly.

Maintenance Insights

This fault inspection chapter is a typical "layered and segmented localization" textbook: Insulation fault P1B41 divides the vehicle high-voltage chain into four segments—"harness end → battery pack end → output port IPU/charger/fast charge → service disconnect switch"—and measures each segment step by step; any abnormal segment can be localized to the smallest repair unit of "replace connector and harness". Threshold values are memorized in pairs—total voltage 362/360 (level 4/3 high), 213/221 (level 4/3 low), cell 4.2/2.5, insulation 500Ω/V and 200MΩ as two rulers. Two details are most valuable: freeze frame snowflake icon—first read "time of fault" data then "current value", which directly distinguishes intermittent from persistent faults, saving repeated test drives; ZLG CAN card to read cell voltages—when total voltage is too low, use an independent CAN tool to read the sum of cell voltages, cross-verify with BMS readings, and determine whether "cells are truly low" or "sampling harness has intermittent connection". This step determines whether to "replace faulty cell" or "replace acquisition harness", which are completely different repair magnitudes. Finally, there is a closing pattern: almost every troubleshooting tree ends with "replace the battery management controller assembly"—the controller is the diagnostic hub of the battery pack; after elimination methods are exhausted and still abnormal, it is the last replaceable part.

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【This article is for reference only】