P0790 trouble code definition
A P0790 trouble code is related to a vehicle’s automatic transmission and the normal/performance switch that changes the shift points for two different driving styles.
What the P0790 code means
P0790 is an OBD-II generic powertrain code for a voltage or resistance problem with the transmission mode controller in that the signal being sent out is not within the manufacturer’s parameters. This will typically not allow the powertrain control module to allow the “power mode” that usually lets the transmission shift later and downshift earlier.
What causes the P0790 code?
Common causes for a P0790 are:
- Faulty transmission mode switch
- Faulty switch wiring and or connectors
What are the symptoms of the P0790 code?
A P0790 can either cause a vehicle to stay in normal mode, or the transmission could fall into “limp-mode” that limits speeds so a vehicle can make it to a repair shop with minimal damage. The overdrive light may also be illuminated.
How does a mechanic diagnose the P0790 code?
A visual inspection of the transmission mode switch will be first, paying close attention to corrosion or liquid intrusion. If wiring appears damaged, it will need to be replaced. Your mechanic will be able to test the normal/power switch itself to determine if it’s functioning properly. If not, it will need to be replaced.
Common mistakes when diagnosing the P0790 code
Some mechanics have reported finding switches that are not so much damaged as corroded. These can be cleaned and replaced but it’s not a wise fix.
How serious is the P0790 code?
It’s rare for a P0790 to cause any symptoms more serious than the inability to access the transmission’s “power mode,” so this code isn’t too serious. If a vehicle does enter limp mode however, it can be more problematic.
What repairs can fix the P0790 code?
The most common repairs for a P0790 are as follows:
- Cleaning the transmission mode switch
- Replacing the transmission mode switch
- Repairing damaged wiring for the transmission mode switch
Additional comments for consideration regarding the P0790 code
Some transmission mode switches are literally a console switch that says “Normal/Power” while others are activated when the transmission is switched to sport or dynamic mode.
Need help with a P0790 code?
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