OBD-II Code P0977 — What It Means & How to Fix It

What Does This Error Mean?

P0977 means Shift Solenoid B Control Circuit is High. The TCM has detected higher voltage than expected on the solenoid B control circuit. This typically means an open circuit or a short to the battery positive (B+) voltage. With solenoid B unable to respond, the gears it controls cannot engage properly. You may experience the transmission skipping certain gears, harsh engagement, or limp mode.

Affected Models

All automatic transmission vehicles 1996 and newer
Common in GM vehicles with 4L60E, 6L80, and 6T40 transmissions
Common in Ford vehicles with 4R70W and 6R80 transmissions
Common in Toyota and Lexus A-series automatic transmissions

Common Causes

Open circuit in the solenoid B control wiring between the TCM and the solenoid
Short to B+ voltage on the solenoid B control wire
Failed solenoid B with an open coil winding
Unplugged or damaged external transmission harness connector
Faulty TCM output driver providing an incorrect high voltage reading

How to Fix It

Check the external transmission harness connector. An unplugged or corroded connector is the simplest cause of a circuit high or open code.

Inspect the connector at both ends — at the transmission case and at the TCM connector if accessible.
Measure solenoid B resistance from the external connector (with the connector unplugged from the transmission). An open reading confirms solenoid or internal harness failure.

Normal resistance for solenoid B is typically 10 to 30 ohms. An open reading (infinite ohms) is the key finding.
Check for a short to B+ on the control wire. Measure voltage on the control wire with the TCM connector unplugged. Voltage present here indicates a B+ short.

A B+ short on a control wire is a wiring harness fault — trace the harness for a chafe point against battery-positive wiring.
If the solenoid is open, drop the pan and replace solenoid B. Inspect the internal harness for the open wire or damaged connector.

On GM 4L60E transmissions, internal harness failures are common at the 20-pin valve body connector crimp points.
Reinstall with new filter and fresh ATF. Clear codes and perform a complete drive cycle. Confirm all gear ranges shift smoothly.

Use a scan tool to confirm solenoid B is being commanded on and off correctly during the test drive.

When to Call a Professional

Solenoid replacement with fluid and filter service costs $250 to $550. Wiring repair runs $150 to $400. TCM replacement and programming is $400 to $800. This is a moderate-cost repair — diagnosis is straightforward with the right tools.

Frequently Asked Questions

What is the difference between P0976 and P0977?

P0976 is circuit low — voltage is below normal (usually a short to ground). P0977 is circuit high — voltage is above normal (usually an open circuit or short to power). Both affect solenoid B but indicate opposite electrical fault conditions.

Can I clear P0977 and drive normally?

Clearing the code does not fix the underlying fault. The code will return immediately when the TCM attempts to activate solenoid B. Driving with a solenoid B fault risks missing gear engagement and clutch pack damage.

Is solenoid B the same as shift solenoid 2?

On many transmissions, yes — solenoid A is SS1 (shift solenoid 1) and solenoid B is SS2 (shift solenoid 2). However, naming conventions vary by manufacturer and transmission model. Always confirm solenoid identity with a vehicle-specific repair manual.