P0977 code definition

The P0977 trouble code notes a problem with the shift solenoid B control circuit.

What the P0977 code means

The P0977 code is a standard OBD trouble code that detects an issue with the shift solenoid valve B control circuit. Shift solenoids are used to help create smooth gear shifts in the automatic transmission. The various shift solenoids control the brakes, bands, and clutches in the transmission, with the B solenoid varying depending on the make and model of the vehicle. The transmission control module (TCM) controls the shift solenoids, and activates and deactivates them as necessary to adjust the gear ratios and facilitate smooth shifting. If the TCM records an abnormal voltage reading from the shift solenoid B control circuit, then that circuit will be disabled, and the powertrain control module (PCM) will note the P0977 code.

What causes the P0977 code?

A few factors can cause the P0977 code to be detected:

What are the symptoms of the P0977 code?

The P0977 trouble code is usually accompanied by the check engine soon Warning Light illuminating on the instrument panel. The vehicle will commonly experience transmission issues, such as harsh shifting, delayed or rough acceleration, and the inability to access certain gears. It is likely that the vehicle will also experience reduced fuel efficiency.

How does a mechanic diagnose the P0977 code?

The P0977 code will be addressed with the aid of a standard OBD-II trouble code scanner. A trained mechanic will use the scanner to look at the freeze frame data and assess the code. Additional trouble codes should also be checked for, and if found, they should be addressed in the order in which the scanner displays them. The trouble codes will then need to be reset, and the vehicle restarted, so the technician can see if the code remains detected. If it does not, then an erroneous trigger or an intermittent error are the most probable culprits.

If the P0977 code returns, then the mechanic will check the transmission fluid. If the fluid is at an insufficient level, then it should be replenished, and the mechanic should thoroughly search for signs of leakage. If the fluid is dirty, it can be flushed out and replaced, but if it is contaminated then there is probably extreme damage to the transmission. This will likely require a replacement, or a full rebuild. Next, the mechanic should visually inspect the electrical components, and replace any wires, connectors, or fuses that are damaged or compromised.

If the issue is not yet found, then a digital volt/ohmmeter can be utilized to help identify the circuit that corresponds to the valve B shift solenoid. After the correct circuit is ascertained, the solenoid, harness, and circuit should all be inspected.

Whenever the technician replaces or repairs a component, the trouble codes should be reset, and the vehicle restarted, so the code can once again be checked for. This helps the technician figure out when the problem is resolved.

Common mistakes when diagnosing the P0977 code

The most frequently made error when diagnosing this code comes from not following the OBD-II diagnosis protocol. It’s very important that technicians always abide by the protocol step by step, as this helps guarantee a diagnosis and repair that is both thorough and efficient.

Shift solenoids are often unnecessarily replaced, when the only issue is something simpler, such as a shorted wire, or dirty transmission fluid.

How serious is the P0977 code?

A vehicle with the P0977 trouble code will still be drivable, though it may experience severe enough transmission problems that it is not practical to drive. If the P0977 code is not addressed, it can cause further damage to the transmission, so it’s important to have the vehicle inspected as soon as the code is noticed.

What repairs can fix the P0977 code?

Repairs for the P0977 trouble code are:

  • Shift solenoid valve B replacement
  • Replacement of the electrical components
  • Replacement or addition of transmission fluid
  • In very rare cases, replacement of the PCM, ECM, or TCM

Additional comments for consideration regarding the P0977 code

The valve B shift solenoid is responsible for different parts of the transmission, depending on the make and model of the vehicle, so the gears that are inaccessible when the P0977 code is detected will differ from car to car.

This code is only applicable for vehicles with automatic transmissions.

Need help with a P0977 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.

This article originally appeared on YourMechanic.com as P0977 OBD-II Trouble Code: Shift Solenoid B Control Circuit High and was authored by Brady Klopfer.


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