The stepper motor is a direct-current (DC) motor that moves from no voltage to full voltage. It can have as many as 180 steps of motion.
If the PCM detects a problem with the transaxle stepper motor, on-board diagnostics will log a P1778 trouble code.
What Does the P1778 Code Mean?
Diagnostic trouble code P1778 stands for “Step Motor Circuit Intermittent.”
The stepper motor serves as a reversible DC motor, moving a shaft back and forth to move a conical valve. Depending on the conical valve’s direction, the engine can either increase or decrease its idle speed.
A typical stepper motor has a permanent magnet and two electromagnets with the PCM controlling the latter. As the computer pulses the windings and changes their polarity, the stepper motor’s armature rotates 90 degrees at a time.
A DTC 1778 is triggered when the PCM detects a problem with the step motor function or its circuit.
For more technical information about P1778, you can read our notes about the stepper motor.
Note: The definition of code P1778 may be different depending on the vehicle manufacturer. Consult the appropriate repair manual or repair database for the exact code definition.
P1778 on Some Nissan Altima Vehicles
In some Nissan Altima vehicles, a P1778 code is detected when there is a great difference between the number of steps for the stepper motor and the actual gear ratio.
This code is most likely to appear when the mechanical system is experiencing some issues, affecting the speed mechanism’s operation.
What are the Common Causes of the P1778 Code?
- Faulty stepper motor
- Wiring issues
What are the Common Symptoms of the P1778 Code?
How to Diagnose the P1778 Code
DTC P1778 is a model-specific powertrain code that usually applies to vehicles with an OBD-II system and a continuously variable transmission (CVT).
Diagnosing this trouble code might involve using a few tools and conducting a visual inspection of the affected part.
If you’re not familiar with the diagnostic procedure yet, it’s always a good idea to have a professional mechanic do the job for you. Otherwise, you can go ahead and do it yourself.
To help you out, here are some videos you can watch to get an idea of what the process usually involves.
How to Fix the P1778 Code
Without the right tools and information, fixing a P1778 code can be frustrating and confusing. If done incorrectly, the repair might do more harm than good.
If you’re not confident in your DIY skills yet, you can always bring your vehicle to a trusted auto repair shop and have a mechanic take care of your daily driver.
But if you think you can handle the job on your own, make sure to have the right equipment and repair manual before proceeding.
Guides like those from Chilton or an ALLDATA subscription contain vehicle-specific repair information, so you might want to check those out before you begin.
More About the Stepper Motor
One familiar application of a stepper motor is an idle air control (IAC) valve on the throttle body that controls engine idle speeds and prevents the engine from stalling. The powertrain control module (PCM) counts the number of steps the stepper motor does to determine its relative position.
But code P1778 has nothing at all to do with idle speed control. The Nissan continuous variable transaxle (CVT) uses a stepper motor to move the active pulley for gear changes. A stepper motor can move its shaft in or out in a very controlled fashion rather than simply spinning the shaft to pull a load, enabling the TCM to provide gear ranges very similar to a conventional transaxle by moving the active pulley in steps.
The Nissan continuous variable transaxle (CVT) uses a stepper motor to move the active pulley for gear changes.–Richard McCuistian, ASE Certified Master Automobile Technician
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