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.

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HOMESERVICE MANUALSMAZDA1999626 ES, 2.5 D, STANDARDREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 392 (SYMPTOM TROUBLESHOOTING (ENGINE CONTROL SYSTEM) AJ)NO.18 COOLING SYSTEM CONCERNS-RUNS COLDDIAGNOSTIC PROCEDURE

1999 Mazda 626 ES, 2.5 D, Standard

Diagnostic procedure

1999 Mazda 626 ES, 2.5 D, StandardSECTION Diagnostic procedure

WARNING: This page is about a different car, the 2005 Mazda MPV. However, it is still accessible from the selected car via links, so may be relevant.

COOLING SYSTEM CONCERNS-RUNS COLD - DIAGNOSTIC PROCEDURE

STEP	INSPECTION		ACTION
1	Is customer complaint "Lack of passenger compartment heat" only?	Yes	Inspect A/C and heater systems.
1		No	Go to next step.
2	Does engine speed continue at fast idle?	Yes	Go to symptom troubleshooting in NO.9 FAST IDLE/RUNS ON .
2	Does engine speed continue at fast idle?	No	Go to next step.
3	Remove thermostat and inspect operation. (See THERMOSTAT REMOVAL/INSTALLATION .) (See THERMOSTAT INSPECTION ) Is thermostat okay?	Yes	Access ECT PID on WDS or equivalent. Inspect both ECT PID and temperature gauge on instrument cluster readings. If temperature gauge on instrument cluster indicates normal range but ECT PID is not same as temperature gauge reading, inspect ECT sensor. If temperature gauge on instrument cluster indicates cold range but ECT PID is normal, inspect temperature gauge and heat gauge unit.
3		No	Replace thermostat.
4	Verify test results. If okay, return to diagnostic index to service any additional symptoms. If malfunction remains, inspect related Service Bulletins and/or On-line Repair Information and perform repair or diagnosis. If vehicle is repaired, troubleshooting completed. If vehicle is not repaired or additional diagnostic information is not available, replace or reprogram PCM.

RENDER: 1.0x

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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.