Safety Warning

DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.

SYS.OK|MANUAL.DB● LIVE

HOMESERVICE MANUALSMAZDA20066 I, 4D SEDAN, AUTOMATICREPAIR AND DIAGNOSIS (SINGLE PAGE)ENGINE PERFORMANCESYSTEMON-BOARD DIAGNOSTIC [ENGINE CONTROL SYSTEM L3)DTC P0126, P0128NOTES

2006 Mazda 6 i, 4D Sedan, Automatic

DTC P0126, P0128: Notes

2006 Mazda 6 i, 4D Sedan, AutomaticSECTION Notes

DTC P0126, P0128 DETECTION CONDITION AND POSSIBLE CAUSES

DTC P0126
DTC P0128

Coolant thermostat stuck open

DETECTION CONDITION

DTC P0126

If the ECT signal never exceeds 71°C {160°F} after engine start for specified period, PCM determines that the coolant thermostat is stuck open.
MONITORING CONDITIONS
- IAT: above -10°C {14°F}
- Vehicle speed: over 9.4 km/h {5.8 mph} [ATX], over 6.3 km/h {3.9mph} [MTX]

DTC P0128

PCM monitors MAF, IAT, VSS and EAT signals and calculate radiator heat radiation ratio while following monitoring conditions are met. If calculated value exceeds threshold, PCM determines that the coolant thermostat is stuck open.
MONITORING CONDITIONS
- ECT at engine start: Below 36°C {97°F}
- IAT: above -10°C {14°F}
- Difference between ECT at engine start and minimum IAT: Below 6°C {10.8°F}
- Vehicle speed: over 32 km/h {20 mph}

Diagnostic support note

This is an intermittent monitor (Engine cooling system).
MIL illuminates if PCM detects above malfunction condition in two consecutive drive cycles or in one drive cycle while DTC for the same malfunction has been stored in PCM.
PENDING CODE is available if PCM detects the above malfunction condition during first drive cycle.
FREEZE FRAME DATA is available.
DTC is stored in PCM memory.
DIAGNOSTIC MONITORING TEST RESULTS is available.

POSSIBLE CAUSE

ECT sensor malfunction
Coolant thermostat malfunction
PCM malfunction

RENDER: 1.0x

NO RELATED

Recommended Tools & Savings

Use the Manual With the Right Hardware

Pair factory procedures with proven DIY tools so the instructions are easier to execute.

Affiliate disclosure: We may earn a commission at no extra cost to you.

Shop Manual-Ready Tools Free Quote Check Quote Shield Pro

When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

• You smell fuel, burning insulation, or see smoke.
• Brakes feel soft, pull hard to one side, or make grinding noises.
• The engine overheats, stalls repeatedly, or misfires under load.
• You are missing required tools, torque specs, or safe lifting equipment.
• You are not confident in the next step or safety outcome.