P0826 OBD-II Trouble Code: Up and Down Switch Input Circuit

P0826 code definition

A P0826 trouble code indicates a problem in the electrical circuit of the upshift/downshift switch to the transmission range correlation circuit. This circuit includes the switch, wiring, connectors, and mode actuator, and is used on vehicles that have manually shiftable automatic transmissions. Related codes include P0827 and P0828.

What the P0826 code means

When the powertrain control module (PCM) detects a variance in the voltage from the upshift/downshift switch circuit that doesn't match the variance as outlined in the manufacturer's specifications, a P0826 trouble code is stored and the check engine light illuminates. The mechanic should keep in mind that some vehicles require multiple failure cycles in order for the check engine light to come on, while the check engine light in some vehicles does not illuminate at all.

What causes the P0826 code?

In addition to shorted, disconnected, or otherwise faulty wiring and connectors, a P0826 trouble code is most commonly caused by liquids spilled on the upshift/downshift switch.

What are the symptoms of the P0826 code?

The most common symptom of a P0826 trouble code is a disabled manual shifter. Another common indicator of a P0826 trouble code is for the transmission control module (TCM) to place the transmission in Limp-in mode, leading to harsh shifting on the part of the transmission and the inability of the torque converter to operate properly. In addition, when a P0826 trouble code is stored, the overdrive light might also flash.

How does a mechanic diagnose the P0826 code?

Diagnosing a P0826 trouble code requires a mechanic to have an advanced scanner, digital volt/ohmmeter, and the manufacturer's wiring diagram for the vehicle in question on hand. The mechanic must also perform the following:

• Perform a visual inspection of all wiring, connectors, and components associated with the upshift/downshift switch circuit.
• If everything appears in working order, connect the scanner to the diagnostic connector and download all freeze frame data and stored trouble codes to help in further diagnosis.
• Clear the code and see if it returns upon testing the system.
• If the code returns check the reference voltage and ground signal of the upshift/downshift switch and actuator.
• If either is open, disconnect all related control modules before testing the continuity and resistance of all circuits. Disconnecting the modules helps prevent damage from a misplaced probe when checking the circuits.
• The mechanic should also use the manufacturer's wiring diagram to test all related circuits using the volt/ohmmeter and then compare their findings to the manufacturer's specifications.
• Clear the code and retest the system, using the scanner to manually activate the upshift switch.
• If the code returns, disconnect and test the PCM for fault.
• The mechanic can also test the normal/performance switch if the transmission mode selector fails to activate manually.
• Clear the code once again and test the system to see if the trouble code returns.

Common mistakes when diagnosing the P0826 code

A common mistake made when diagnosing a P0826 trouble code is for the mechanic to overlook spilled liquid on the upshift/downshift switch as the cause of the problem and instead erroneously focus on faulty transmission wiring as the source of the problems causing the code storage.

How serious is the P0826 code?

While you can drive with a stored P0826 trouble code, the transmission problems caused by the issues that cause this code can make it more difficult, if not impossible, to drive a vehicle.

What repairs can fix the P0826 code?

To repair a P0826 trouble code the mechanic must do the following:

• Replace any faulty, damaged, or defective wiring, connectors, or components.
• Replace the upshift/downshift switch or actuator if they check out as bad after inspection.
• If any of the related circuits, connectors, and components test as faulty, replace them as well.
• Replace the upshift solenoid if it is not working properly.
• Though rare, a faulty PCM can also cause this trouble code storage. Replace the PCM if it is found to be bad.
• A final option is to replace the normal/performance switch if the transmission mode selector fails to work properly.

Need help with a P0826 code?

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