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P0781 OBD-II Trouble Code: 1-2 Shift Malfunction

check engine light

P0781 code definition

When your vehicle’s PCM stores a P0781 code, it means that the PCM has identified a problem in the 1-2 shift function.

What the P0781 code means

The automatic transmission in your vehicle uses shift solenoids to move fluid through hydraulic circuits, and make changes in your gear ratio. This affects the way your vehicle shifts, increasing and decreasing speed, optimizing fuel efficiency and maximizing engine performance.

What causes the P0781 code?

When the gear ratio detected is not in sync with the gear ratio needed, then the PCM records a P0781 code, and your Check Engine Light will come on and the code will be stored. Sometimes, though, repeated failures may take place before the Check Engine Light comes on.

Common causes are:

  • Bad shift solenoid

  • Blockages in the transmission fluid lines

  • Failure within the transmission itself

  • Contaminated transmission fluid

  • Bad PCM (this is rare)

What are the symptoms of the P0781 code?

You might actually notice no symptoms at all, until the problem becomes worse. Then, you may experience:

  • Transmission slippage

  • A burning smell due to an overheated transmission

  • Trouble shifting

  • Lower fuel economy

  • Vehicle entering “limp in mode” in order to prevent damage to the transmission Your Check Engine Light will also come on.

How does a mechanic diagnose the P0781 code?

First, your mechanic will attach a digital voltmeter or scanner to your vehicle to see what codes come up. In addition to P0781, codes P0782-P0784 may appear. These codes generally indicate slippage in the transmission.

Now, your mechanic will:

  • Check your transmission fluid to make sure that it is not low or dirty

  • Do a “sniff test” to make sure that the fluid does not give off a burned smell

  • If the fluid smells burned, check the transmission pan for debris

  • If there is debris, flush and replace the fluid and install a new torque converter

  • Check the wiring and harness to see if anything needs to be replaced

Finally, once the diagnostics have been completed, the mechanic will take your car for a test drive to see how it performs, and upon bringing it back, use the scanner again to see if the codes reappear.

A good mechanic will always re-test the vehicle to make sure that any maintenance or repairs have been successful, and will re-test as many times as are necessary in order to ensure that the trouble codes go away and you are driving safely.

Common mistakes when diagnosing the P0781 code

Sometimes, mechanics assume the worst, and blame the PCM or the shift solenoid, when the problem is actually dirty or low fluid. The PCM is hardly ever the issue, and shift solenoids are seldom the problem.

How serious is the P0781 code?

Trouble shifting is hardly ever going to get you killed if you’re just driving around town. If you’re attempting to pass on the Interstate, though, it could be more problematic. You do not have to park your car and call for a tow truck, but you should get this checked out at your earliest convenience. You don’t want any surprises when you’re driving at high speeds.

What repairs can fix the P0781 code?

With a P0781 code, most of the time it is not a matter of repair so much as it is maintenance. Often, topping off or replacing your transmission fluid will correct the problem.

Need help with a P0781 code?

At YourMechanic, we will be pleased to dispatch a qualified mechanic to your home, or your place of work, to do any repairs you might need. Whether the problem is a P0781 code or something else, we are here for you. Call us at 1-800-701-6230, or if you prefer, book an appointment online using our convenient form. We will be happy to provide you with a free quote before we come to see you.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details
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