NO.9 FAST IDLE/RUNS ON [MZI-3.7]

id0103d2801500

9 | FAST IDLE/RUNS ON
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DESCRIPTION | • Engine speed continues at fast idle after warm-up. • Engine runs after ignition switch is turned to off position.
POSSIBLE CAUSE | • CHT sensor malfunction • Improper load signal input ― Refrigerant pressure sensor malfunction ― Communication error between instrument cluster and PCM ― Erratic signal from climate control unit (A/C switch, fan switch malfunction) ― Evaporator temperature sensor malfunction ― Open or short circuit in wiring harness between front climate control unit terminal 2A and instrument cluster terminal 1C ― Erratic signal from PSP switch ― TR switch malfunction ― Communication error between TCM and PCM • Improper operation of drive-by-wire control system • Air leakage from intake-air system • Cruise control system operation improperly • APP sensor malfunction

Diagnostic procedure

STEP | INSPECTION | RESULTS | ACTION
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1 | Access the PCM PID ECT using the M-MDS. (See ON-BOARD DIAGNOSTIC TEST [MZI-3.7].) Start and warm up the engine to normal operating temperature. Is the ECT PID between 82—112 °C {180—233 °F}? | Yes | Go to the next step.
No | ECT PID is higher than 112 °C {233 °F}: • Go to the symptom troubleshooting “NO.17 COOLING SYSTEM CONCERNS-OVERHEATING”. (See NO.17 COOLING SYSTEM CONCERNS-OVERHEATING [MZI-3.7].) ECT PID is less than 82 °C {180 °F}: • Go to the symptom troubleshooting “NO.18 COOLING SYSTEM CONCERNS-RUNS COLD”. (See NO.18 COOLING SYSTEM CONCERNS-RUNS COLD [MZI-3.7].)
2 | Turn the ignition switch to the ON position (Engine off). Retrieve any PCM DTCs using the M-MDS. (See ON-BOARD DIAGNOSTIC TEST [MZI-3.7].) Are there any DTCs displayed? | Yes | DTC is displayed: • Go to the appropriate DTC inspection. (See DTC TABLE [MZI-3.7].)
No | No DTC is displayed: • Go to the next step.
3 | Access and monitor the following PCM PIDs using the M-MDS: (See ON-BOARD DIAGNOSTIC TEST [MZI-3.7].) • AC_REQ • PSP • TR Are PID values normal? (See PCM INSPECTION [MZI-3.7].) | Yes | Go to the next step.
No | If the AC_REQ PID is not normal: • Inspect the following: ― Refrigerant pressure sensor ― Front climate control unit terminal 2A voltage ― Wiring harness between front climate control unit terminal 2A and instrument cluster terminal 1C If the TR PID is not normal: • Inspect the TR switch and related wiring harness for vibration or intermittent open/short circuit. If the PSP PID is not normal: • Inspect the PSP switch and related wiring harness for vibration or intermittent open/short circuit. Repair or replace the malfunctioning part according to the inspection results.
4 | Is air leakage felt or heard at intake-air system components while racing the engine to higher speed? | Yes | Repair or replace the malfunctioning part according to the inspection results.
No | Inspect the following: • Drive-by-wire control system operation • APP sensor (See ACCELERATOR PEDAL POSITION (APP) SENSOR INSPECTION [MZI-3.7].) • Cruise control switch (built-in steering switch) (See CRUISE CONTROL SWITCH INSPECTION [MZI-3.7].) Repair or replace the malfunctioning part according to the inspection results.
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].)