Fault code P0816 is called “Downshift Switch Circuit Malfunction” but in different programs it may be called differently. This fault designation applies to all vehicles equipped with OBD-II.
Technical description and explained code P0816
This diagnostic trouble code (DTC) is a generic transmission code. Error P0816 is considered a general code because it applies to all makes and models of vehicles. Although the specific repair steps may vary slightly depending on the model.
This code applies to vehicles with automatic transmission or manual shift variator. It is set when the transmission control module detects a fault in the downshift switch circuit.
The manual shift design features may be a selector lever or push-button controls on the shift selector or steering wheel. But in all cases, the system allows the driver to manually shift gears on the automatic.
Activation of the appropriate control initiates downshifting. The signals are transmitted to the transmission control module (TCM) via CAN (Control Area Network) protocols.
All relevant components such as the switch, wiring, connectors and mode actuator are part of the circuitry. Most of which is built into either the console around the gear selector in the cabin or on or near the steering wheel.
The PCM controls transmission gear selection by comparing downshift switch inputs to ensure continuity. In addition, the PCM monitors the voltage in the downshift switch circuit to ensure that it is within the set parameters.
If the PCM detects that the transmission gear selection does not match the downshift switch gear selection signal. Or the voltage in the switch circuit is not within acceptable parameters. Code P0816 may be stored and the Malfunction Indicator Light (MIL) may illuminate.
Symptoms of vehicle malfunctions
The main signal that an error P0816 has occurred is the Malfunction Indicator Lamp (MIL) is also known as the CheckEngine Light.
It can also be warning signs such as:
- The “Check engine” control lamp on the control panel will light up (the code will be stored as a fault).
- It may be difficult to shift gears while driving.
- The shift indicator light reflects the wrong gear.
- Disable manual gear shift function.
- Transmission may be put into emergency mode.
- There may be no symptoms other than a stored fault code.
A stored P0816 code indicates that a potentially serious fault has been detected. The conditions that contributed to the stored code should be corrected as soon as possible.
Factors that can cause this error code
The error code P0816 can mean that one or more of the following problems have occurred:
- The downshift switch is defective.
- Faulty mode control device.
- Corroded, broken or shorted wiring or connectors.
- Poor electrical connection.
- Sometimes faulty PCM or programming error is the cause.
How to fix or reset OBD-2 code P0816
Some suggested steps for troubleshooting and fix the error code P0816:
- Connect an OBD-II scanner to the vehicle’s diagnostic connector and read all stored data and error codes.
- Clear the error codes, perform a test drive, and check if the P0816 fault appears again.
- Visually inspect the electrical wires and connectors.
- If necessary, repair or replace any shorted, broken, damaged, or corroded components.
- Check the derailleur switch.
- Test and replace the module if necessary.
Diagnose and repair of problems
The first thing to do when troubleshooting error P0816 is to check the electrical part for damage. In today’s vehicles, electrical and electronic signals require good cabling for proper data transmission. Any malfunctions, such as breaks, disconnected connectors or corrosion, can interrupt signals, leading to transmission control failures.
Check the battery pack, as some PCM and TCM modules are sensitive to low voltage. If the battery is low, the system may detect this as a failure. Make sure the battery is delivering at least 12 volts and that the alternator is running properly, at least 13 volts at idle.
If the car does not show a failure caused by faulty wiring, the problem is probably caused by a worn downshift switch. Its replacement should solve the problem with the P0816 error. But don’t overlook fuses either, because a blown fuse is a common problem.
PCM and TCM failure is a rare cause, but sometimes it happens. But since replacing a control module often requires tethering or reprogramming it. It is better to contact a professional craftsman in this case.
On which vehicles does this problem occur most frequently
Fault code P0816 can occur on different vehicles but there are statistics on which brands this occurs most often. Here is a list of some of them:
- Acura
- Audi
- Chevrolet (Cruze)
- Ford (Focus)
- Mercedes-Benz (Sprinter)
- Opel (Astra)
- Vauxhall
- Volkswagen (Polo)
Fault code P0816 can sometimes be found with other errors. The most common are the following: P2779, P2780, P2781, P2782.
