01 The Science of Flight: How Aircraft Stay in the Air • 02 The Fleet Manager Who Runs 200 Vans Explains How To Cut Mai… • 03 Expert Guide: Why is my car stalling and the engine over he… • 04 P0016 - Crankshaft Position Camshaft Position Correlation B… • 05 Why Dirty Grounds Cause More Car Problems Than People Reali… • 06 The $30 Device That's Making Car Thieves Invisible to Police • 07 Mass Air Flow Sensor (MAF): How It Works, Symptoms and Prob… • 08 P0075, P0076, and P0077: Intake valve control solenoid circ… • 09 From AEB to AR HUD: A Deep Dive into Top 2024 Car Tech Feat… • 10 Why Does Car AC Only Work When Driving? Comprehensive Cause… •

DTC codes / P09xx · Transmission / P0977

P0977Shift Solenoid 'B' Control Circuit High

P0977 indicates that the transmission control module (TCM) has detected an abnormally high voltage on the control circuit for shift solenoid 'B', which is used to manage gear shifts. The TCM expects the circuit voltage to be within a specific range when the solenoid is commanded on or off, and a high reading suggests an open circuit, a short to voltage, or a faulty solenoid.

SystemPowertrain
Code typeGeneric (all makes)
SeverityMedium
Fix difficultyProfessional
AreaTransmission

Symptoms you may notice

  • The check engine light or transmission warning light illuminates on the dashboard.
  • The transmission may enter limp mode, limiting the vehicle to a single gear or a reduced set of gears.
  • Harsh or delayed gear shifts, or the transmission may fail to shift at all.
  • The engine may rev unusually high or low during acceleration due to incorrect gear selection.
  • Often no symptoms besides the warning light, especially if the fault is intermittent.

Common causes, most likely first

  1. A faulty shift solenoid 'B' with an open internal coil or high resistance.
  2. Damaged or corroded wiring or connectors in the solenoid control circuit, causing an open circuit.
  3. A short to voltage in the wiring between the TCM and the solenoid.
  4. A failed transmission control module (TCM) or internal driver circuit.
  5. Poor electrical connections at the transmission pass-through connector or ground points.
  6. Contamination or debris in the transmission fluid interfering with solenoid operation.

How to diagnose and fix it

  1. Use an OBD-II scanner to retrieve the code and check for any related transmission codes.
  2. Inspect the transmission fluid level and condition for signs of contamination or burning.
  3. Visually inspect the wiring harness and connectors at the solenoid and TCM for damage or corrosion.
  4. Measure the resistance of shift solenoid 'B' with a multimeter and compare to the manufacturer's specification.
  5. Check for voltage on the control circuit with the key on and engine off to identify a short to voltage.
  6. Test the TCM output signal with an oscilloscope or a bidirectional scan tool if available.
  7. Replace the faulty solenoid, repair wiring, or replace the TCM as needed, then clear the code and verify the repair.

Don't overlook the wiring harness

  • A common cause of P0977 is a chafed or broken wire in the harness near the transmission, often due to heat or vibration, which can be missed if only the solenoid is tested.
  • The code can set intermittently due to a poor connection at the transmission pass-through connector, so wiggle-testing the harness while monitoring live data is a valuable step.
  • A high voltage reading does not always mean the solenoid is defective; a short to voltage elsewhere in the circuit can produce the same code.
  • Some vehicles use a single solenoid for multiple functions, so a failure may affect several gears and mimic other transmission problems.
  • After repairs, the TCM may need to relearn adaptive shift strategies, so a scan tool with transmission reset capabilities is often required.

Can I keep driving with P0977?

If the vehicle is in limp mode or shifting erratically, avoid highway driving and seek repair promptly to prevent transmission damage. If only the warning light is on and the vehicle drives normally, you can drive cautiously to a workshop, but avoid heavy loads or aggressive acceleration.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

Running on fumes Free guides aren't free to make. Top up the tank. Any amount, one time. Fuel the Garage