Roewe Plug-in Hybrid High-Voltage Battery Pack Management System (BMS) Fault Diagnosis Guide

Fault Background

The Roewe plug-in hybrid (846 manual) high-voltage battery pack control module (BMS/ESS) manages the most sensitive signal family in the vehicle: main high-voltage interlock (HVIL), dual current sensors (CAB/LEM, one on positive and one on negative), one-piece replaceable service disconnect switch (MSD, which splits the battery high voltage into two halves; the high-voltage management module HVM monitors the two high-voltage points above and below via high-voltage sense wires connected to the MSD), insulation detection circuit, pre-charge circuit. The main connector BY216 carries, in addition to KL30×2, signals such as HVIL Src/Rtn, PT CAN_H/L, HY CAN_H/L, Wake Up. The DTC thresholds are highly quantified: main fuse voltage difference >10V, total voltage <260V/>410V, LEM voltage <0.2V/>4.8V for 10s, interlock duty cycle <40%/<60% for 5s, pre-charge duration >500ms, low-voltage battery <9V/>16V for 1s; stored/history DTCs are also automatically cleared after 40 wake/standby cycles. This article is organized as a diagnostic guide in the order: "Insulation → Voltage/Fuse → Pre-charge/Interlock → Current → MSD/Crash → Low-voltage Supply".

Insulation Family (P0A97 / P1E04 / P1E05 / P1E06 / P1EB2)

The current detection module simultaneously monitors battery current and insulation; low insulation is reported over the vehicle network and the insulation resistance detection circuit is self-checked.

Diagnostic Path: ① Use diagnostic scan tool to read "high-voltage system insulation resistance" and check if within reasonable range (appendix); if not → inspect/replace high-voltage battery pack; ② Check HV002/HY003 connectors for looseness/poor contact/twisting/corrosion/contamination/deformation; ③ Ignition OFF, vehicle stationary for more than 5 minutes, operate the manual service disconnect switch to disconnect high-voltage battery power, disconnect the battery negative terminal; ④ Measure between terminals of the high-voltage connector on the high-voltage battery and between terminals and ground to confirm no high voltage is present; ⑤ Use insulation tester to measure insulation value of the high-voltage battery system (test voltage should be higher than the high-voltage battery pack voltage); ⑥ Disconnect HV002/HY003, resistance between each terminal and ground should be in the megohm range (HV002-1/2, HY003-1/2/3); ⑦ If code persists → inspect/replace high-voltage battery pack.

Voltage and Fuse

• P0A9A/P0A9B Total voltage too low/high: Total voltage valid and <260V / >410V (normal 260~410V) → limp home, high-voltage output disconnected when vehicle stops; Action: Check mounting position/wiring harness/connector wear or corrosion → clear codes and retest → if code returns, first software update BMS to confirm version → if still present, open-cover repair, seek professional technical support.
• P0A95 Main fuse blown: HVM monitors the two high-voltage points above and below the MSD via MSD high-voltage sense wires; voltage difference across fuse >10V triggers → limits current output then disconnects high voltage; Action: Check battery pack and MSD for wear/corrosion → clear codes and retest → if code returns, disconnect MSD and check internal terminal continuity; if open, replace MSD; otherwise inspect/replace high-voltage battery pack.

Pre-charge and Interlock

• P0C78/P1E0D Pre-charging: To prevent inrush surge on power-up, BMS monitors pre-charge time and energy—pre-charge duration >500ms (P0C78) or pre-charge energy exceeds limit within specified time (P1E0D) → immediately disconnect high voltage (for P1E0D, BMS waits 5s then enters sleep); Check battery pack and on-board charger mounting position/wiring harness/connectors; if code persists after retest, replace component;
• P1E01/P1E02 AC charging interlock circuit short to ground/power: High-voltage interlock circuit signal between BMS and OBC duty cycle <40% (to ground) / <60% (to power) for 5s; The interlock circuit is used to "verify high-voltage connector reliability via low voltage"—if any component connector is loose or open, the interlock opens, and the system cannot energize high voltage;
• P1E2B/P1E2C High-voltage interlock circuit input failure-high/low, P0A0C/P0A0D Main high-voltage interlock circuit failure-low/high: Same family troubleshooting.

Current Sensor Family (CAB/LEM Dual Sensors)

The high-voltage battery pack has one current sensor on each of the positive and negative terminals (CAB and LEM); if the current values from the two sensors differ too much, P0B13 is set. LEM voltage thresholds: P1E09 short to ground—LEM voltage <0.2V for 10s; P1E0A short to power—>4.8V for 10s (fault warning lamp illuminated, extinguishes 10s after recovery). Over-limit family: P1E1C/P1E1D discharge/charge current severely over-limit → immediately disconnect high voltage; P1E1E/P1E1F discharge/charge current over-limit.

MSD and Crash

• P1E25 Manual service disconnect switch not installed: Detected that MSD is not plugged in (or inertia switch circuit open) → immediately disconnect high voltage; Clearing condition is plugging in/closing the circuit; Check MSD mounting position, interlock wiring harness, connector wear/corrosion; if code returns, first software update, if still present, open-cover repair.
• P1E26 Crash: BMS communicates with airbag control module via high-speed CAN; crash circuit activation for 1 time sets the code (cleared if not activated for 10s). Diagnosis: Read "crash circuit status" reasonable value → BY216-5 ↔ BY079-2, BY216-13 ↔ BY079-1 continuity test → resistance to ground infinite → voltage to ground 2~3V → if code persists, inspect/replace battery management controller or airbag control module.

Low-Voltage Supply and Cell Family

• P1EC0/P1EC1 Low-voltage battery voltage too low during/after relay engagement: Low-voltage battery voltage <9V → cannot de-energize relay; U1562 >16V for 1s, U1563 <9V for 1s. Diagnosis: Check engine compartment fuse box connector BY016 and BY216 → BY016-5 ↔ BY216-1/14 continuity test, resistance to power/ground infinite → inspect/replace battery management controller or engine compartment fuse box.
• P1E8B~P1E92 Voltage monitoring unit (CMU) 01~08 voltage detection fault, P1E7x CMU temperature detection fault (including P1BCE CMU 12): Open pack to check sense wiring harness and CMU; if code persists after software update, open-cover repair.
• P1EAE/P1EAF AC charging current/voltage inconsistent with BMS demand; P1E86/P1E88 AC charger requests emergency power-down / DC charger reports emergency power-down: Troubleshoot per corresponding charger manual.

Safety Warnings

• This article is for technical reference. High-voltage battery pack repair must be performed by qualified technicians (electrician certificate + company training authorization) per OEM specifications.
• Before all circuit tests: Ignition OFF, vehicle stationary for more than 5 minutes, operate the manual service disconnect switch to disconnect high-voltage battery power, disconnect the battery negative terminal, and measure to confirm no high voltage at high-voltage connector terminals.
• The insulation tester's test voltage must be higher than the high-voltage battery pack voltage; terminal-to-ground resistance must be in the megohm range.
• Open-cover repair and BMS replacement require software update and programming; for crash-related checks, avoid live measurements on airbag circuits.

Repair Insights

The most valuable three things to learn from the Roewe BMS code table: First, the "confirm no high voltage" step in insulation diagnosis is written into the procedure—after waiting 5 minutes, disconnecting MSD, and disconnecting the negative terminal, you must still use a multimeter to measure between high-voltage connector terminals to confirm no voltage before starting insulation testing; this "voltage verification" is more reliable than any verbal discipline. Second, the main fuse is diagnosed by "voltage difference across terminals >10V"—the MSD is a one-piece replaceable type; the HVM monitors the two high-voltage points above and below via high-voltage sense wires, so a blown fuse can be located without opening the pack. Third, the low-voltage voltage code thresholds are divided into two levels: P1EC0/1 is "during/after relay engagement <9V" → cannot de-energize relay (this is a safety action, not a fault symptom); U1562/63 are the actual battery issues (>16V/<9V for 1s)—first distinguish between "low-voltage supply insufficient causing BMS to refuse operation" and "battery fault", don't treat U codes as P codes. Finally, remember the interlock family duty cycle thresholds: 40% (to ground) / 60% (to power) for 5s; use an oscilloscope or diagnostic scan tool to read duty cycle to quickly determine whether the interlock circuit is "leaking to ground" or "leaking to power".

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【This article is for reference only】