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DTC P1778: Malfunction of Stepper Motor
 
 
 
 
STEPPER MOTOR SYSTEM CIRCUIT
Refer to .
 
 
DIAGNOSTIC FUNCTION
TCM conducts the fault detection of the stepper motor by comparing the target value of the primary pulley speed with the actual value. (Target value: Actual secondary pulley speed multiplied by pulley ratio corresponding to stepper motor position) (Actual measurement value: Actual primary pulley speed)
 
 
DESCRIPTIONS OF MONITOR METHODS
The difference between the target value of the primary pulley speed and the actual measurement value is greater than the standard value, the difference between the target gear ratio and the actual gear ratio is 0.3 or greater, and this status continues for 5 seconds.
 
 
MONITOR EXECUTION
  • Transmission range: D
  • Throttle valve opening: 1/8 or more
  • Engine speed: 450 r/min or more
  • CVT fluid temperature: from 20 to 180°C (68 to 356°F)
 
 
MONITOR EXECUTION CONDITIONS (OTHER MONITOR AND SENSOR)
Other Monitor (There is no temporary DTC stored in memory for the item monitored below)
  • Not applicable
Sensor (The sensor below is determined to be normal)
  • Not applicable
 
 
LOGIC FLOW CHARTS (Monitor Sequence)
 
 
DTC SET CONDITIONS
Check Conditions
  • Transmission range switch position: D.
  • Vehicle speed: 10 km/h (6.2 mph) or more.
  • Accelerator pedal position sensor voltage: 1.37 volts or more.
  • Engine speed: 450 r/min or more.
Judgment Criteria
  • secondary pulley speed - Primary pulley speed: 1000 r/min or more. (5 seconds)
 
 
OBD-II DRIVE CYCLE PATTERN
Ignition switch: ON (start the engine and keep it for 10 seconds or more)
 
 
PROBABLE CAUSES
  • Malfunction of TCM
  • Malfunction of valve body assembly (Faulty stepper motor)
 
 
DIAGNOSIS
STEP 1. Check other diagnostic trouble codes.
Are other diagnostic trouble codes stored?
Carry out the appropriate troubleshooting.
Go to Step 2.
 
STEP 2. Symptom recheck after erasing diagnostic trouble code
Is the check result normal?
Intermittent malfunction
Replace the TCM, and then go to Step 3.
 
STEP 3. Retest the system.
Is the check result normal?
The inspection is complete.
Replace the valve body assembly.