NO.18 COOLING SYSTEM CONCERNS-RUNS COLD [MZI-3.7]

id0103d2802400

18 | COOLING SYSTEM CONCERNS—RUNS COLD
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DESCRIPTION | • Engine takes excessive time to reach normal operating temperature.
POSSIBLE CAUSE | • A/C and heater system malfunction • Cooling fan system malfunction • Thermostat malfunction • Improper water temperature gauge operation ― CHT sensor malfunction ― Instrument cluster malfunction

Diagnostic procedure

STEP | INSPECTION | RESULTS | ACTION
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1 | Is customer complaint “Lack of passenger compartment heat” only? | Yes | Inspect the A/C and heater system. Repair or replace the malfunctioning part according to the inspection results.
No | Go to the next step.
2 | Does the engine speed continue at fast idle? | Yes | Go to the symptom troubleshooting “NO.9 FAST IDLE/RUNS ON”. (See NO.9 FAST IDLE/RUNS ON [MZI-3.7].)
No | Go to the next step.
3 | Inspect the cooling fan control system operation. (See ENGINE CONTROL SYSTEM OPERATION INSPECTION [MZI-3.7].) Does the cooling fan control system function properly? | Yes | Go to the next step.
No | Repair or replace the malfunctioning part according to the inspection results.
4 | Cool down the engine. Remove the thermostat and inspect the operation. (See THERMOSTAT REMOVAL/INSTALLATION [MZI-3.7].) (See THERMOSTAT INSPECTION [MZI-3.7].) Is the thermostat normal? | Yes | Inspect the water temperature gauge. (See INSTRUMENT CLUSTER INSPECTION.) Repair or replace the malfunctioning part according to the inspection results. • If the water temperature gauge reading is normal, inspect the CHT sensor. (See CYLINDER HEAD TEMPERATURE (CHT) SENSOR INSPECTION [MZI-3.7].) • Repair or replace the malfunctioning part according to the inspection results.
No | Replace the thermostat. (See THERMOSTAT REMOVAL/INSTALLATION [MZI-3.7].)
5 | • Verify test results. ― If normal, return to diagnostic index to service any additional symptoms. (See SYMPTOM DIAGNOSTIC INDEX [MZI-3.7].) ― If malfunction remains, inspect related Service 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 the PCM. (See PCM REMOVAL/INSTALLATION [MZI-3.7].)