Technical Description of OBD-II Trouble Code
Malfunction in the Circuit for Normal/Performance Switch
What does that signify?
This is a generic diagnostic trouble code (DTC) for powertrain and is commonly found in OBD-II vehicles. This can include vehicles from various manufacturers such as GMC, Chevrolet, Ford, Buick, Dodge, etc. Although it is a generic code, the specific repair steps may vary depending on the year, make, model, and powertrain configuration of the vehicle.
The Transmission Control Module (TCM) monitors all the sensors and switches involved in the operation of the transmission. In today’s age, automatic transmissions (also known as A/T) have more advanced features than ever before.
For example, the TCM may monitor and control cruise control along with other modules. In the case of this article, it pertains to a normal/performance mode switch that is enabled by the operator to adjust the ratios and shift patterns for higher upshift points and faster downshift points. The proper functioning of this switch is crucial for the performance function and other related systems. However, the specific switch and its location may vary significantly between manufacturers, so it is important to identify the correct switch for your particular fault and make and model of vehicle.
The ECM (Engine Control Module) triggers the MIL (Malfunction Indicator Lamp) and sets the P0790 code when it detects a malfunction in the normal/performance switch circuit. In most cases, these switches are located on or near the shift lever. In a stalk-style shifter, it may be a button on the end of the lever. In console-style shifters, it may be located on the dash or console. The location can vary significantly between vehicles, so consult the service manual for the specific location.
An example of a stalk-mounted transmission mode switch (similar to normal/performance switch):
What is the severity of this DTC?
I would classify this as a low severity code. However, it is advisable to avoid aggressive or hard driving as it may put unnecessary stress on the transmission and its components. Use common sense when driving in this situation.
What are some of the symptoms of the code?
Symptoms of a P0790 trouble code may include:
What are some of the common causes of the code?
Possible causes for the P0790 code may include:
What are some troubleshooting steps for P0790?
Basic Step #1
The starting point for troubleshooting may vary depending on the tools and references available to you. If your scanner has monitoring capabilities (DATA STREAM), you can use it to monitor the values and operation of your normal/performance switch. Toggle the switch on and off to see if your scanner detects the inputs. Keep in mind that there may be a slight delay, so wait a few seconds when monitoring switches.
In addition, if your scanner indicates that the mode switch is inoperative, you can try jumping some pins at the switch’s connector to test the circuit. If the circuit is ruled out using this method and the switch is still not functioning, proceed to test the switch itself. These are general guidelines, and with a capable scan tool, troubleshooting can be relatively easy if you know what to look for. Refer to the service manual for specifications and procedures.
Basic Step #2
If possible, test the switch itself. In most cases, these switches are simply used to signal the appropriate module(s) (e.g. TCM, BCM, ECM) to implement modified shift patterns. Many of these switches are on/off style. Therefore, you can use an ohm meter to perform a simple continuity test and determine the functionality of the sensor. Keep in mind that these sensors are sometimes integrated into the shift lever, so make sure to research which connectors and pins you need to monitor with your multimeter.
NOTE: As with any transmission fault, always ensure that fluid levels and quality are adequate and properly maintained.
