P0816 OBD-II Trouble Code: Downshift Switch Circuit

P0816 code definition

The P0816 code is a generic powertrain code related to the transmission, including sensor faults. In this case, the downshift switch circuit may have a malfunction.

Codes related to the P0816 include:

• P2779: Downshift Switch Circuit Range/Performance
• P2780: Downshift Switch Circuit Low
• P2781: Downshift Switch Circuit High
• P2782: Downshift Switch Circuit Intermittent/Erratic

What the P0816 code means

When a P0816 code is stored, the Engine Control Module (ECM) has found a malfunction with the downshift switch circuit. The downshift switch circuit includes the switch, connectors and system wiring, and the mode actuator. Located near the shifter in the passenger compartment of the vehicle, the downshift switch is used on vehicles with an automatic transmission that can be shifted manually (an automated manual).

Using solenoids to actuate fluid transfer between hydraulic circuits for each gear, the ECM calculates the data and initiates downshifting or upshifting. When the vehicle’s ECM is sent a voltage reading or resistance signal that is outside of the manufacturer's preset parameters, a P0816 code can be stored.

What causes the P0816 code?

Several problems may cause a P0816 code including:

• Damaged or defective transmission gear selection switch
• Open or shorted gear selection switch harness
• Liquids getting into the downshift switch
• Damaged, corroded or poor electrical connection to the transmission gear selection switch

What are the symptoms of the P0816 code?

Symptoms of a P0816 code may include:

• Check Engine Light may illuminate
• There may be no symptoms other than a stored P0816 code
• Manual shifter function may be disabled
• Vehicle may go into “limp” mode
• Overdrive light may flash

How does a mechanic diagnose the P0816 code?

A mechanic may use several methods to diagnose a P0816 trouble code, including:

• Utilize an OBD-II scanner to check for a stored P0816 trouble code
• Check for reference voltage and ground signals at the downshift switch
• Check for reference voltage and ground signals at the downshift actuator
• If either circuit is open, use a volt/ohmmeter to check for continuity
• Test all connected circuits and switches for continuity and resistance
• Visually inspect all wiring and connectors related to the downshift switch circuit for damage or corrosion

Common mistakes when diagnosing the P0816 code

A common cause of a P0816 code or malfunction in the downshift switch is simply liquids being spilled onto the switch. Often, this can be overlooked and the cause of the fault is assumed to be faulty transmission wiring.

How serious is the P0816 code?

Because a vehicle’s safe driving operation may be impacted due to faults that store a P0816 code, this code is considered a potentially serious code. When this code appears, it is recommended to immediately take your vehicle to your local service center or mechanic for repair and diagnosis.

What repairs can fix the P0816 code?

Several repairs can fix a P0816 trouble code and include:

• Repair or replace any damaged or faulty downshift switch circuits and connectors
• Replace damaged downshift switch
• Replace damaged or defective downshift solenoid
• Repair or replace any other damaged or defective circuits or connectors
• Repair or replace “normal/performance” switch, if applicable
• Repair or replace a damaged or defective ECM (rare)
• Clear all codes, test-drive the vehicle, and rescan to see if any codes reappear
• Repair or replace any damaged or burned wiring or connectors related to the downshift switch circuit

Need Help with a P0816 Code?

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