Diagnostic trouble code · Mazda
P0126 on Mazda vehicles
P0126 is named on 32 Mazda model years (2018–2026): 796 manufacturer filings and 7 owner reports in NHTSA’s files, across CX-5, Mazda6, Mazda3, CX-3, CX-30.
Powertrain 32 model years 796 manufacturer filings 7 owner reports
Which Mazda model years name P0126
Source: NHTSA manufacturer communications and complaints| Model year | Filed under | Bulletins | Owner reports |
|---|---|---|---|
| 2019 Mazda CX-5 | Engine | 36 | 2 |
| 2020 Mazda CX-5 | Engine | 36 | 1 |
| 2020 Mazda Mazda6 | Engine | 37 | — |
| 2019 Mazda Mazda6 | Engine | 37 | — |
| 2019 Mazda Mazda3 | Engine | 35 | 1 |
| 2018 Mazda CX-5 | Engine | 36 | — |
| 2020 Mazda CX-3 | Engine | 35 | — |
| 2020 Mazda CX-30 | Engine | 35 | — |
| 2020 Mazda Mazda3 | Engine | 35 | — |
| 2019 Mazda CX-3 | Engine | 35 | — |
| 2018 Mazda Mazda6 | Engine | 35 | — |
| 2021 Mazda CX-5 | Engine | 31 | 2 |
| 2021 Mazda CX-3 | Engine | 32 | — |
| 2021 Mazda CX-30 | Engine | 32 | — |
| 2021 Mazda Mazda6 | Engine | 32 | — |
| 2021 Mazda Mazda3 | Engine | 31 | — |
| 2022 Mazda CX-30 | Engine | 29 | — |
| 2022 Mazda Mazda3 | Engine | 29 | — |
| 2023 Mazda CX-30 | Engine | 28 | — |
| 2023 Mazda CX-5 | Engine | 27 | 1 |
| 2023 Mazda Mazda3 | Engine | 28 | — |
| 2022 Mazda CX-5 | Engine | 28 | — |
| 2024 Mazda CX-5 | Engine | 27 | — |
| 2025 Mazda CX-5 | Engine | 21 | — |
| 2024 Mazda Mazda3 | Engine | 6 | — |
| 2026 Mazda CX-30 | Engine | 5 | — |
| 2026 Mazda Mazda3 | Engine | 5 | — |
| 2024 Mazda CX-30 | Engine | 5 | — |
| 2018 Mazda Mazda3 | Engine | 4 | — |
| 2025 Mazda Mazda3 | Engine | 2 | — |
| 2025 Mazda CX-30 | Engine | 1 | — |
| 2018 Mazda CX-3 | Engine | 1 | — |
A model year is listed because the code is named in its own record — a bulletin filed against it, or an owner’s complaint about it — not because every one of these vehicles sets it. Counts are documents in NHTSA’s files, not failure rates.
Engine 778 Not specified 16 Equipment 6 Power Train 1
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What Mazda owners said
Source: NHTSA complaint databaseOwners’ own words, scrubbed of anything identifying. Unverified reports filed with NHTSA — what was said, not a finding that it was true.
Summary of Events: Purchase Date: 05/27/2023 Coolant Warning: In January 2025, I received a coolant temperature warning (code P0126) indicating insufficient coolant temperature
When I took it to a dealer, they stated that the check engine light must come on from DTC P0126:00 before they can address the problem under warranty
Mazda filings that name P0126
Source: NHTSA manufacturer communicationsBulletins and campaigns Mazda filed with NHTSA whose summary names P0126. Quote the document number at the service desk — it is a diagnosis the maker has already written down.
- SA-035-20 Service bulletin2020-02-28 · Engine And Engine Cooling
- Some customers may experience the CHECK ENGINE LIGHT ON with DTC P0126:00 (Thermostat stuck open) and one or more of the following symptoms: The engine takes longer to warm up. The engine temperature gauge fluctuates. The low coolant temperature indicator (blue) light stays on longer or comes on while driving. Poor heater performance, especially at idle.
- SA-035-20a Service bulletin2020-03-11 · Engine And Engine Cooling
- Some customers may experience the CHECK ENGINE LIGHT ON with DTC P0126:00 (Thermostat stuck open) and one or more of the following symptoms: ï· The engine takes longer to warm up. ï· The engine temperature gauge fluctuates. ï· The low coolant temperature indicator (blue) light stays on longer or comes on while driving. ï· Poor heater performance, especially at idle.
- SA-035-20b Service bulletin2020-12-02 · Engine And Engine Cooling
- Some customers may experience the CHECK ENGINE LIGHT ON with DTC P0126:00 (Thermostat stuck open) and one or more of the following symptoms: The engine takes longer to warm up. The engine temperature gauge fluctuates. The low coolant temperature indicator (blue) light stays on longer or comes on while driving. Poor heater performance, especially at idle.
- SA-017-21 Service bulletin2021-02-25 · Engine And Engine Cooling
- Some customers may experience the CHECK ENGINE LIGHT ON with DTC P0126:00 (Thermostat stuck open) and one or more of the following symptoms: The engine takes longer to warm up. The engine temperature gauge fluctuates. The low coolant temperature indicator (blue) light stays on longer or comes on while driving. Poor heater performance, especially at idle.
- SA-017-21a Service bulletin2021-03-08 · Engine And Engine Cooling
- CHECK ENGINE LIGHT ON WITH DTC P0126:00 AND ENGINE RUNNING COOLER THAN NORMAL / POOR HEATER PERFORMANCE / LOW ENGINE COOLANT TEMPERATURE (BLUE) LIGHT ON: Some customers may experience the CHECK ENGINE LIGHT ON with DTC P0126:00 (Thermostat stuck open) and one or more of the following symptoms: The engine takes longer to warm up. The engine temperature gauge fluctuates. The low coolant temperature
- 01-011-21-3800 Service bulletin2021-04-22 · Engine And Engine Cooling
- Some customers may experience the CHECK ENGINE light ON with DTC P0126:00 (Thermostat stuck open) and one or more of the following symptoms: The engine takes longer to warm up, The engine temperature gauge fluctuates, The low coolant temperature indicator (blue) light stays on longer or comes on while driving, Poor heater performance, especially at idle. NOTE: Vehicles with SKYACTIV-G 2.5T are no
- 01-011-21-3800a Service bulletin2021-09-27 · Engine And Engine Cooling
- Some customers may experience the CHECK ENGINE light ON with DTC P0126:00 (Thermostat stuck open) and one or more of the following symptoms: The engine takes longer to warm up, The engine temperature gauge fluctuates, The low coolant temperature indicator (blue) light stays on longer or comes on while driving, Poor heater performance, especially at idle. NOTE: Vehicles with SKYACTIV-G 2.5T are not
- 01-013-22 Service bulletin2022-10-19 · Engine And Engine Cooling
- Some customers may experience the CHECK ENGINE light ON with DTC P0126:00 (Thermostat stuck open) and one or more of the following symptoms: * The engine takes longer to warm up * The engine temperature gauge fluctuates * The low coolant temperature indicator (blue) light stays on longer or comes on while driving * Poor heater performance, especially at idle NOTE: * Vehicles with SKYACTIV-G
- 01-005-23 Service bulletin2023-02-16 · Engine And Engine Cooling
- Some customers may experience the check engine light ON with DTC P0126:00 (Thermostat stuck open) and one or more of the following symptoms: The engine takes longer to warm up. The engine temperature gauge fluctuates. The low coolant temperature indicator (blue) light stays on longer or comes on while driving. Poor heater performance, especially at idle. NOTE: Vehicles with SKYACTIV-G 2.5T are not
- 01-005-23a Service bulletin2023-12-20 · Engine And Engine Cooling
- Some customers may experience the check engine light ON with DTC P0126:00 (Thermostat stuck open) and one or more of the following symptoms: The engine takes longer to warm up The engine temperature gauge fluctuates The low coolant temperature indicator (blue) light stays on longer or comes on while driving Poor heater performance, especially at idle
- 01-005-24 Service bulletin2024-06-11 · Engine
- Some customers may experience a check engine light ON with DTC P0126:00 (Thermostat stuck open) and one or more of the following symptoms: Engine takes longer to warm up. Engine temperature gauge fluctuates. Low coolant temperature indicator (blue) light stays on longer or turns on while driving. Poor heater performance, especially at idle. NOTE: Vehicles with SKYACTIV-G 2.5T are not applicable to
- 01-005-24a Service bulletin2024-06-28 · Engine
- Some customers may experience a check engine light ON with DTC P0126:00 (Thermostat stuck open) and one or more of the following symptoms: Engine takes longer to warm up. Engine temperature gauge fluctuates. Low coolant temperature indicator (blue) light stays on longer or turns on while driving. Poor heater performance, especially at idle. NOTE: Vehicles with SKYACTIV-G 2.5T are not applicable to
What P0126 means
Source: SAE J2012 / OBD-IIP0126 sits in the generic range of the OBD-II standard, so it means the same thing on every vehicle sold in the United States — but WhichTrim does not carry a definition for it and will not invent one. What is on this page is the record: who named it and on what.
A stored code names the test that failed, never the part that caused it. The record above is what Mazda and its owners have filed about it; the code’s page across every make has the whole file.
From here
Common questions
Source: NHTSA files and the OBD-II standardIs P0126 a known problem on Mazda vehicles?
It is a documented one: NHTSA's files hold 796 manufacturer filings and 7 owner reports naming P0126 on 32 Mazda model years (2018–2026). Whether it is a problem on one particular car is a diagnosis, not a count — but a bulletin that names the code on your model year is the place to start.
Which Mazda models does P0126 appear on most?
2019 CX-5 (38 documents), 2020 CX-5 (37 documents), 2020 Mazda6 (37 documents).
Does P0126 on a Mazda mean it is recalled?
No. Recalls are filed by campaign and matched by VIN; no recall is triggered by a scan tool. Check the VIN at nhtsa.gov/recalls, or open the model year's page here for the campaigns filed against it.