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P0999 Shift Solenoid F Control Circuit High

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P0999 code definition

The P0999 code identifies a problem in an automatic transmission in the shift solenoid F circuitry and sets the code.

What the P0999 code means

A P0999 code the OBD-II generic code for a problem between the transmission control module and the shift solenoid F control circuit that is high in the ECM or engine control module memory.

What this means is that the operation of the automatic transmission is impaired because the TCM, in shifting through specific gear ratios (activating or deactivating) shift solenoids to operate clutches or breaks in the transmission, encounters a failed check. The TCM will check the function of the solenoid valves by testing resistance and speed sensors. If a check fails, which is what happens when the shift solenoid F control circuit high code appears, it disables that circuit.

What causes the P0999 code?

There are a few common causes for the P0999 code, and they include:

  • Prolonged vehicle storage in which wiring harnesses and insulation degrade or are destroyed by pests
  • Poor repair work in which a technician failed to route harnesses properly during a radiator or cylinder head replacement
  • Faulty wiring
  • Burnt out solenoid

What are the symptoms of the P0999 code?

A P0999 code comes with some frightening symptoms that can include the inability of the driver to be able to engage the vehicle in the "D" mode. They may also be unable to use other gears, or experience very poor acceleration, high engine revving in gear and harsh shifting or poor fuel economy. The vehicle also sets the code.

How does a mechanic diagnose the P0999 code?

Diagnostics for the P0999 require a digital ohm meter and the wiring diagram for the vehicle. The circuits will be checked between the TCM and the transmission, and a harness check is done. All connectors are checked and a circuit check will be done as well. The diagnostics also look for ECM faults, open circuits, and a check of the solenoid. If no issues are found, it may be the transmissions internal sub harness and the solenoid.

How serious is the P0999 code?

The P0999 code can easily prevent the vehicle from operating. It may even make it impossible to shift into the "D" gear, or other gears while in operation. The fact that it can also lead to high revving when shifting gears means that there is the serious risk of engine damage or even catastrophic damage during use of the vehicle while it is recording this code.

What repairs can fix the P0999 code?

To address the P0999 code, the following repairs are recommended:

  • Perform an electrical check using a digital ohm meter and the vehicle's wiring diagram, looking at the circuits between the TCM and the transmission itself.
  • Check the wiring harness beginning at the ECM and TCM and following them to the transmission. Look for indications of damage and make repairs. Check connectors and intermediate connectors.
  • Check the circuitry with the key off, using the digital ohm meter to determine the circuits responsible for shift solenoid F. Perform a resistance test from the ECM or TCM to the solenoid and the harness. If there is acceptable resistance, it may be that the ECM is the problem.
  • Check the harness for continuity by removing the transmission connector and measuring resistance at the TCM connector.
  • Check the solenoid by measuring its resistance at the connector, and if this is acceptable it is likely that a sub harness repair is needed.

Additional comments for consideration regarding the P0999 code

The circuit checks are meant to determine if there is an open solenoid to blame or if there is a break in the sub harness. A final step in repair may be to bench test the solenoid in question using a jumper to ensure it is functional.

Need help with a P0999 code?

YourMechanic offers certified mobile mechanics who will come to your home or office to diagnose and repair your vehicle. Get a quote and book an appointment online or speak to a service advisor at 1-800-701-6230.

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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