P0780 code definition
The P0780 code means that that car’s computer has detected a malfunction with the transmission shifting.
What the P0780 code means
The P0780 code means that there has been an abnormality with the transmission shifting. Note that this code only applies to automatic transmissions. This code is also often associated with other, similar codes, such as P0755 Shift Solenoid B Malfunction. Automatic transmissions use shift solenoids to move fluid through internal circuits and channels to create pressure differences, thus shifting gears. If fluid does not move as expected, and there is a variance between the actual gear ratio and the gear ratio expected based on engine inputs (throttle position, engine speed, etc.), then the computer will set the P0780 code.
What causes the P0780 code?
There are many potential causes of the P0780 code, and they are similar to the causes of the P0755 code. They include the following:
- A failed shift solenoid
- Dirty or contaminated transmission fluid
- Low transmission fluid
- Internal blockages that prevent fluid from moving correctly
- A faulty PCM (rare)
- A faulty TCM (rare)
What are the symptoms of the P0780 code?
Symptoms of the P0780 code can range dramatically, depending on the make and model in question, as well as the actual underlying cause. They include the following:
- The Check Engine light illuminated but no other symptoms
- Failure to shift into or out of gear
- Transmission stuck in “limp-home” mode
- Transmission overheating
- Harsh shifting
- Transmission slipping
- Decreased fuel efficiency
How does a mechanic diagnose the P0780 code?
As with most other DTC codes, the P0780 code will first need to be diagnosed by connecting an OBD II scanner to the car’s communications port. This is located on the driver side under the dash, usually. The technician will read the code (or codes) and then clear the system. A test drive will be needed to make sure the code resets.
The next step will be to check the level of transmission fluid (low fluid is one of the most common causes). If the transmission fluid is low, it will need to be topped off, the code cleared and the car test driven again. Sometimes, this is all that is needed. If the transmission fluid is dirty, it will need to be drained and refilled (possibly with a filter replacement). If the transmission fluid smells burned or contains finings, the pan will need to be removed and the technician will inspect for signs of damage. In this instance, a transmission rebuild may be necessary.
If the fluid level and condition are good, the mechanic will then inspect the shift solenoids, as well as their wiring harnesses. While failed solenoids may cause the code, it is also possible that there is damage to the harness, or corroded wiring connections. The technician will also check the pump’s pressure using a manual gauge to ensure that pressure readings are in line with manufacturer specifications. If they are not, the pump may be clogged or failing.
Common mistakes when diagnosing the P0780 code
The most common mistake is replacing shift solenoids without conducting a full, thorough inspection. Often, the underlying problem is related to transmission fluid level or condition. It may also be related to a faulty shift solenoid circuit, rather than the solenoid itself.
How serious is the P0780 code?
The P0780 code is serious, even if you’re not experiencing drivability problems yet. It can lead to serious transmission damage, causing expensive repairs.
What repairs can fix the P0780 code?
There are several potential fixes for the P0780 code, depending on the underlying cause. They include the following:
- Topping off the transmission fluid
- Changing dirty, burnt transmission fluid
- Replacing failed shift solenoids
- Repairing damaged wiring
- Cleaning corroded connections
Additional comments for consideration regarding the P0780 code
Regular transmission maintenance can help prevent the P0780 code by keeping your transmission fluid clean and at the correct level.
Need help with a P0780 code?
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