ACTMS Error on BYD: What’s Actually Going On and How to Deal With It
ACTMS Error on BYD So your BYD threw an ACTMS warning. The screen lit up, you’ve never seen this one before, and you’re not sure how worried to be.
Here’s what it actually means: ACTMS stands for Air Conditioning and Thermal Management System. It’s the system that manages heat across two critical areas — the cabin climate (heating and cooling) and the high-voltage battery pack. When something goes wrong in either of those areas, the car logs an ACTMS fault and tells you about it.
This is not a tire pressure warning. It’s not a minor nuisance. The thermal management of a high-voltage battery is serious business — but it’s also frequently triggered by something simple. Let’s work through it.
What You Might Notice
- ACTMS warning or error message on the central display
- Air conditioning not cooling or heating properly
- Reduced driving range or performance, especially in hot or cold weather
- The car limiting charging speed or power output
- A “Contact BYD Service” message appearing alongside the fault
What Usually Causes It
1. Low Coolant in the Thermal Management Circuit
BYD’s thermal system uses a dedicated liquid cooling loop — separate from a regular combustion engine — to regulate battery temperature. If the coolant level drops (due to a slow leak or air trapped in the system), the ACTMS throws a fault.
Check first: Open the front hood and locate the thermal management coolant expansion tank. The level should be between MIN and MAX. If it’s low, top it up with the correct coolant type (check your owner’s manual — BYD specifies this) and see if the warning clears after a drive cycle.
2. Software Glitch
BYD vehicles are heavily software-driven. An ACTMS fault sometimes appears after a failed OTA update, a system reboot, or simply a temporary sensor hiccup. A power cycle often clears it.
How to try: Park safely, turn the car completely off, get out with the key, lock the doors, and wait 10–15 minutes for the car to enter deep sleep. Then restart and see if the fault is gone.
3. AC Compressor or Valve Fault
If the ACTMS warning comes with noticeably poor cabin cooling or heating, the issue is likely in the AC compressor, a refrigerant valve, or the HVAC control module. This won’t clear on its own and needs professional diagnosis.
4. Battery Thermal Regulation Issue
If the warning appears specifically during fast charging or when climbing long steep grades, the battery’s thermal regulation system is struggling to keep the pack within its safe temperature window. The car may limit charging speed or power output as a protective measure. This is the system working as intended — but the underlying cause (degraded cooling, a faulty pump, or a sensor error) still needs to be found.
5. 12V Battery Instability
Less common, but a weak or failing 12V auxiliary battery can cause widespread sensor faults across BYD systems, including ACTMS. If you’re seeing multiple unrelated warnings at the same time, check the 12V battery health.
6. Coolant Pump or Temperature Sensor Failure
The thermal loop relies on an electric coolant pump. If that pump is failing or a temperature sensor is reading incorrectly, the ECU sees an out-of-range value and flags the fault.
How Serious Is This?
It depends on what’s triggering it.
Lower urgency: The car drives normally, AC works fine, and the warning appeared once and cleared after a restart. Likely a software glitch — monitor it.
Medium urgency: The warning keeps coming back but performance seems normal. Get it scanned soon — something is intermittently failing.
High urgency: AC has stopped working, range has dropped noticeably, the car is limiting power or charging speed, or the warning appeared during fast charging and didn’t clear. Don’t delay — the battery thermal system is directly involved and needs professional attention.
How to Diagnose It
Step 1 — Power cycle the vehicle Park, turn off completely, get out with the key, lock the doors, wait 10–15 minutes. This allows all systems to fully shut down. Restart and see if the fault clears.
Step 2 — Check the coolant level Open the hood and check the thermal management coolant expansion tank. Low coolant is one of the most common triggers and the easiest fix.
Step 3 — Check for a software update Go to Settings → Software Update. BYD pushes OTA updates regularly and has addressed ACTMS-related bugs in past releases. Install any pending updates before spending money on repairs.
Step 4 — Scan for fault codes A standard OBD2 scanner won’t give you much here. BYD stores manufacturer-specific fault codes that require a compatible diagnostic tool. A BYD dealer or a specialist with BYD-compatible software can pull the full fault log and tell you exactly what the system detected and when.
Step 5 — Describe the context to a technician When did it appear — during charging, while driving, at startup? Does the AC still work? Has range changed? This context significantly speeds up diagnosis.
What It Might Cost
| Issue | Estimated Cost |
|---|---|
| Power cycle (DIY) | Free |
| Coolant top-up (DIY) | $10–$30 |
| Software update at dealer | $0–$80 |
| Coolant pump replacement | $200–$500 |
| AC compressor repair | $400–$900 |
| Temperature sensor replacement | $100–$300 |
| ACTMS module replacement | $300–$800 |
Costs vary by region and BYD model. Always get a diagnostic scan before authorizing any repairs.
Related Warnings
- Battery Temperature Warning — Often appears alongside ACTMS in thermal-related faults
- Reduced Power / Range — The car protecting the battery when thermal management fails
- AC Fault — Direct HVAC system issue, may share the same root cause
- U0100 — Communication loss with ECM, can appear alongside
Questions People Actually Ask
Can I keep driving with the ACTMS error on? If the car drives normally and the AC works, you can drive carefully in the short term. If performance or range has dropped, or if the warning appeared during charging, treat it as urgent.
Will it go away on its own? If it was a one-time software glitch, yes — a power cycle often clears it. If it’s a hardware fault (coolant, pump, sensor, compressor), no. It will return and likely get worse.
Is this covered under warranty? If it’s a hardware or software fault within the warranty period, it should be covered. Contact your BYD dealer before paying for any diagnosis or repair — let them assess it first.
Is ACTMS the same on all BYD models? The system exists across BYD’s lineup but implementation details vary. The Atto 3, Seal, Dolphin, and Han all have thermal management systems, but fault codes and repair procedures differ by model. Always specify your model when contacting a dealer.
Why did this appear right after I fast-charged? Fast charging generates significant heat in the battery pack. If the thermal system is struggling — low coolant, a weak pump, or a sensor issue — fast charging is often what exposes it first.
This guide is for informational purposes only. ACTMS faults involve high-voltage systems. For an accurate diagnosis and any repair work, always consult a qualified BYD technician or authorized service center.
