# P0126 on the 2020 Mazda CX\-5

The bulletins listed name this code in NHTSA's summary, or are about the same components. A bulletin or a recall listed here may apply to the model year. None of it is a diagnosis.

Nobody has written a description of this code yet.

## Bulletins for this model year that name P0126

- [11030701](https://open.wenmarpro.com/bulletins/11030701), 2026-04-04: Subject: TSB 01\-001/26 Warranty and Parts Kit Update INCLUDES: Warranty Extension Program \- Special Service Program \(SSP\) D8 Check Engine Light ON with DTC P0126:00, 2018\-2025 CX\-5, 2019\-2023 Mazda3, 2019\-2022 CX\-3, 2018\-2021 Mazda6, 2020\-2023 CX\-30 Dear Mazda Dealer Colleagues, Mazda Motor Corporation has made a change regarding related parts to TSB 01\-001/26 which also impacts Warranty Extension Special Service Program \(SSPD8\). Parts Ordering and Warranty Claims: Effective March 5, 2026 only the related parts kit PYY2\-15\-SAY can be ordered and claimed for any repair. The two separate parts PYFB\-15\-169 and PE13\-15\-296 can no longer be claimed with repaired dates of March 5, 2026 and later. There is no change to the main part, the Plug PYY3\-15\-SA1. We have updated the TSB 01\-001/26 and SSPD8 Repair Procedure and Parts \& Warranty Information on Mazda Global Service Support \(MGSS\) to reflect this change.
- [11030700](https://open.wenmarpro.com/bulletins/11030700), 2026-04-04: Subject: TSB 01\-001/26 Warranty and Parts Kit Update INCLUDES: Warranty Extension Program \- Special Service Program \(SSP\) D8 Check Engine Light ON with DTC P0126:00, 2018\-2025 CX\-5, 2019\-2023 Mazda3, 2019\-2022 CX\-3, 2018\-2021 Mazda6, 2020\-2023 CX\-30 Dear Mazda Dealer Colleagues, Mazda Motor Corporation has made a change regarding related parts to TSB 01\-001/26 which also impacts Warranty Extension Special Service Program \(SSPD8\). Parts Ordering and Warranty Claims: Effective March 5, 2026 only the related parts kit PYY2\-15\-SAY can be ordered and claimed for any repair. The two separate parts PYFB\-15\-169 and PE13\-15\-296 can no longer be claimed with repaired dates of March 5, 2026 and later. There is no change to the main part, the Plug PYY3\-15\-SA1. We have updated the TSB 01\-001/26 and SSPD8 Repair Procedure and Parts \& Warranty Information on Mazda Global Service Support \(MGSS\) to reflect this change.
- [11030598](https://open.wenmarpro.com/bulletins/11030598), 2026-04-02: 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. Vehicles with SKYACTIV\-G 2.5T are not applicable to this service information. DTC P0126:00 is not required to be present to perform this repair. If the vehicle has not previously had the repair specified in this TSB and is exhibiting any of the listed symptoms, proceed with the repair procedure outlined in this bulletin. If DTC P2B61:00 \(Coolant Control Valve Circuit Range/Performance\) is present along with DTC P0126:00, this TSB does not apply. Diagnose the symptom and/or stored DTCs according to the procedures in MGSS. If only DTC P0126:00 is present and this TSB has already been completed previously, this bulletin does not apply, diagnose the symptom and/or stored DTCs according to the procedures in MGSS. This concern may be caused if the coolant control valve fail\-safe thermostat opens at a temperature lower than the normal temperature due to a deformation of the thermostat diaphragm. To eliminate the concern, the water flow control valve specification has been modified. Affected vehicles will require PCM reprogramming with the Mazda Modular Diagnostic System \(M\-MDS\), using either a\) Mazda Diagnostic and Repair Software \(MDARS\) or b\) Mazda Integrated Diagnostic System \(IDS\) 140.04 or later software.
- [11029542](https://open.wenmarpro.com/bulletins/11029542), 2026-03-04: SSPD8 \- Check Engine Light ON with DTC P0126:00 \- WARRANTY EXTENSION For certain 2018\-2025MY CX\-5, 2019\-2023MY Mazda3, 2019\-2022MY CX\-3, 2018\-2021MY Mazda6, 2020\-2023MY CX\-30 that are equipped with the suspected coolant control valve, the warranty coverage for specific repair of the fail\-safe thermostat is extended to: 15 years \(180 months\) or 150,000 miles \(240,000 km\) whichever comes first, from the original warranty start date. CONDITION OF CONCERN: On certain subject vehicles, the check engine light is illuminated with DTC P0126:00 \(Thermostat stuck open\) stored in memory and one or more of the following symptoms may occur: \- 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. Mazda Motor Corporation has made a significant repair change to TSB 01\-003/25 which also impacts Warranty Extension Special Service Program \(SSPD8\). Repair Procedure Update: Effective December 8th all repairs applicable to TSB 01\-003/25 or SSPD8 must follow the new repair procedure. The repair now replaces the thermostat with a dummy plug for the coolant control valve \(CCV\) along with a required software update for the PCM. Prior Repairs: Any repairs previously completed with the replacement of the thermostat or coolant control valve assembly does not require a re\-repair unless there is a verified failure following the diagnosis in the TSB. It is expected that there will be no further repairs made for this concern once the plug and software update has been completed. Therefore, a return visit for symptoms related to the TSB or SSP must contact the Technical Hotline for assistance. VITALLY IMPORTANT\!: There must be a “Software Update” record for the PCM when using MDARS or IDS. • MDARS \- If there is no Software Update entry in MDARS or the Collect Diagnostic Information \(ODR Update\) is not completed \(or both\), the vehicle will not be considered repaired and the warranty claim will be rejected. • IDS – Vehicles programed with IDS must Collect Diagnostic Data, and that data must be attached to the warranty claim. If the data is not attached to the claim, the vehicle will not be considered repaired and the warranty claim will be rejected, denied or debited. Failure to complete the above will require the vehicle to return to the dealership and be re\-repaired at the dealer’s expense with great inconvenience to the Mazda customer. Failure to perform the software update could also potentially damage the engine which would not be covered by warranty and would expose your dealership to the cost of repairs.
- [11028143](https://open.wenmarpro.com/bulletins/11028143), 2026-02-03: SSPD8 \- Check Engine Light ON with DTC P0126:00 \- WARRANTY EXTENSION For certain 2018\-2025MY CX\-5, 2019\-2023MY Mazda3, 2019\-2022MY CX\-3, 2018\-2021MY Mazda6, 2020\-2023MY CX\-30 that are equipped with the suspected coolant control valve, the warranty coverage for specific repair of the fail\-safe thermostat is extended to: 15 years \(180 months\) or 150,000 miles \(240,000 km\) whichever comes first, from the original warranty start date. CONDITION OF CONCERN: On certain subject vehicles, the check engine light is illuminated with DTC P0126:00 \(Thermostat stuck open\) stored in memory and one or more of the following symptoms may occur: \- 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. Mazda Motor Corporation has made a significant repair change to TSB 01\-003/25 which also impacts Warranty Extension Special Service Program \(SSPD8\). Repair Procedure Update: Effective December 8th all repairs applicable to TSB 01\-003/25 or SSPD8 must follow the new repair procedure. The repair now replaces the thermostat with a dummy plug for the coolant control valve \(CCV\) along with a required software update for the PCM. Prior Repairs: Any repairs previously completed with the replacement of the thermostat or coolant control valve assembly does not require a re\-repair unless there is a verified failure following the diagnosis in the TSB. It is expected that there will be no further repairs made for this concern once the plug and software update has been completed. Therefore, a return visit for symptoms related to the TSB or SSP must contact the Technical Hotline for assistance. VITALLY IMPORTANT\!: There must be a “Software Update” record for the PCM when using MDARS or IDS. • MDARS \- If there is no Software Update entry in MDARS or the Collect Diagnostic Information \(ODR Update\) is not completed \(or both\), the vehicle will not be considered repaired and the warranty claim will be rejected. • IDS – Vehicles programed with IDS must Collect Diagnostic Data, and that data must be attached to the warranty claim. If the data is not attached to the claim, the vehicle will not be considered repaired and the warranty claim will be rejected, denied or debited. Failure to complete the above will require the vehicle to return to the dealership and be re\-repaired at the dealer’s expense with great inconvenience to the Mazda customer. Failure to perform the software update could also potentially damage the engine which would not be covered by warranty and would expose your dealership to the cost of repairs.
- [11028142](https://open.wenmarpro.com/bulletins/11028142), 2026-02-03: SSPD8 \- Check Engine Light ON with DTC P0126:00 \- WARRANTY EXTENSION For certain 2018\-2025MY CX\-5, 2019\-2023MY Mazda3, 2019\-2022MY CX\-3, 2018\-2021MY Mazda6, 2020\-2023MY CX\-30 that are equipped with the suspected coolant control valve, the warranty coverage for specific repair of the fail\-safe thermostat is extended to: 15 years \(180 months\) or 150,000 miles \(240,000 km\) whichever comes first, from the original warranty start date. CONDITION OF CONCERN: On certain subject vehicles, the check engine light is illuminated with DTC P0126:00 \(Thermostat stuck open\) stored in memory and one or more of the following symptoms may occur: \- 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. Mazda Motor Corporation has made a significant repair change to TSB 01\-003/25 which also impacts Warranty Extension Special Service Program \(SSPD8\). Repair Procedure Update: Effective December 8th all repairs applicable to TSB 01\-003/25 or SSPD8 must follow the new repair procedure. The repair now replaces the thermostat with a dummy plug for the coolant control valve \(CCV\) along with a required software update for the PCM. Prior Repairs: Any repairs previously completed with the replacement of the thermostat or coolant control valve assembly does not require a re\-repair unless there is a verified failure following the diagnosis in the TSB. It is expected that there will be no further repairs made for this concern once the plug and software update has been completed. Therefore, a return visit for symptoms related to the TSB or SSP must contact the Technical Hotline for assistance. VITALLY IMPORTANT\!: There must be a “Software Update” record for the PCM when using MDARS or IDS. • MDARS \- If there is no Software Update entry in MDARS or the Collect Diagnostic Information \(ODR Update\) is not completed \(or both\), the vehicle will not be considered repaired and the warranty claim will be rejected. • IDS – Vehicles programed with IDS must Collect Diagnostic Data, and that data must be attached to the warranty claim. If the data is not attached to the claim, the vehicle will not be considered repaired and the warranty claim will be rejected, denied or debited. Failure to complete the above will require the vehicle to return to the dealership and be re\-repaired at the dealer’s expense with great inconvenience to the Mazda customer. Failure to perform the software update could also potentially damage the engine which would not be covered by warranty and would expose your dealership to the cost of repairs.
- [11028092](https://open.wenmarpro.com/bulletins/11028092), 2026-02-03: 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. • This concern may be caused if the coolant control valve fail\-safe thermostat opens at a temperature lower than the normal temperature due to a deformation of the thermostat diaphragm. To eliminate the concern, the water flow control valve specification has been modified.
- [11028091](https://open.wenmarpro.com/bulletins/11028091), 2026-02-03: 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. • This concern may be caused if the coolant control valve fail\-safe thermostat opens at a temperature lower than the normal temperature due to a deformation of the thermostat diaphragm. To eliminate the concern, the water flow control valve specification has been modified.
- [11027028](https://open.wenmarpro.com/bulletins/11027028), 2026-01-06: SSPD8 \- Check Engine Light ON with DTC P0126:00 \- WARRANTY EXTENSION For certain 2018\-2025MY CX\-5, 2019\-2023MY Mazda3, 2019\-2022MY CX\-3, 2018\-2021MY Mazda6, 2020\-2023MY CX\-30 that are equipped with the suspected coolant control valve, the warranty coverage for specific repair of the fail\-safe thermostat is extended to: 15 years \(180 months\) or 150,000 miles \(240,000 km\) whichever comes first, from the original warranty start date. CONDITION OF CONCERN: On certain subject vehicles, the check engine light is illuminated with DTC P0126:00 \(Thermostat stuck open\) stored in memory and one or more of the following symptoms may occur: \- 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. Mazda Motor Corporation has made a significant repair change to TSB 01\-003/25 which also impacts Warranty Extension Special Service Program \(SSPD8\). Repair Procedure Update: Effective December 8th all repairs applicable to TSB 01\-003/25 or SSPD8 must follow the new repair procedure. The repair now replaces the thermostat with a dummy plug for the coolant control valve \(CCV\) along with a required software update for the PCM. Prior Repairs: Any repairs previously completed with the replacement of the thermostat or coolant control valve assembly does not require a re\-repair unless there is a verified failure following the diagnosis in the TSB. It is expected that there will be no further repairs made for this concern once the plug and software update has been completed. Therefore, a return visit for symptoms related to the TSB or SSP must contact the Technical Hotline for assistance. VITALLY IMPORTANT\!: There must be a “Software Update” record for the PCM when using MDARS or IDS. • MDARS \- If there is no Software Update entry in MDARS or the Collect Diagnostic Information \(ODR Update\) is not completed \(or both\), the vehicle will not be considered repaired and the warranty claim will be rejected. • IDS – Vehicles programed with IDS must Collect Diagnostic Data, and that data must be attached to the warranty claim. If the data is not attached to the claim, the vehicle will not be considered repaired and the warranty claim will be rejected, denied or debited. Failure to complete the above will require the vehicle to return to the dealership and be re\-repaired at the dealer’s expense with great inconvenience to the Mazda customer. Failure to perform the software update could also potentially damage the engine which would not be covered by warranty and would expose your dealership to the cost of repairs.
- [11027024](https://open.wenmarpro.com/bulletins/11027024), 2026-01-06: SSPD8 \- Check Engine Light ON with DTC P0126:00 \- WARRANTY EXTENSION For certain 2018\-2025MY CX\-5, 2019\-2023MY Mazda3, 2019\-2022MY CX\-3, 2018\-2021MY Mazda6, 2020\-2023MY CX\-30 that are equipped with the suspected coolant control valve, the warranty coverage for specific repair of the fail\-safe thermostat is extended to: 15 years \(180 months\) or 150,000 miles \(240,000 km\) whichever comes first, from the original warranty start date. CONDITION OF CONCERN: On certain subject vehicles, the check engine light is illuminated with DTC P0126:00 \(Thermostat stuck open\) stored in memory and one or more of the following symptoms may occur: \- 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. Mazda Motor Corporation has made a significant repair change to TSB 01\-003/25 which also impacts Warranty Extension Special Service Program \(SSPD8\). Repair Procedure Update: Effective December 8th all repairs applicable to TSB 01\-003/25 or SSPD8 must follow the new repair procedure. The repair now replaces the thermostat with a dummy plug for the coolant control valve \(CCV\) along with a required software update for the PCM. Prior Repairs: Any repairs previously completed with the replacement of the thermostat or coolant control valve assembly does not require a re\-repair unless there is a verified failure following the diagnosis in the TSB. It is expected that there will be no further repairs made for this concern once the plug and software update has been completed. Therefore, a return visit for symptoms related to the TSB or SSP must contact the Technical Hotline for assistance. VITALLY IMPORTANT\!: There must be a “Software Update” record for the PCM when using MDARS or IDS. • MDARS \- If there is no Software Update entry in MDARS or the Collect Diagnostic Information \(ODR Update\) is not completed \(or both\), the vehicle will not be considered repaired and the warranty claim will be rejected. • IDS – Vehicles programed with IDS must Collect Diagnostic Data, and that data must be attached to the warranty claim. If the data is not attached to the claim, the vehicle will not be considered repaired and the warranty claim will be rejected, denied or debited. Failure to complete the above will require the vehicle to return to the dealership and be re\-repaired at the dealer’s expense with great inconvenience to the Mazda customer. Failure to perform the software update could also potentially damage the engine which would not be covered by warranty and would expose your dealership to the cost of repairs.