What this code means
P0977 may mean the ECM/PCM is seeing an unexpectedly high electrical condition on the CVT shift solenoid valve B circuit.
What the vehicle may do
- The vehicle may show a transmission warning or check-engine light.
- CVT operation may feel abnormal, or the vehicle may have limited transmission performance.
- In some cases, the code may be intermittent and the vehicle may appear to drive normally during inspection.
Possible fault areas
- Possible ignition feed or fuse circuit issue.
- Possible open wiring in the solenoid power or control circuit.
- Possible shift solenoid valve B or solenoid wire harness issue.
- Possible PCM software or PCM-side control issue.
Diagnostic path
Opening context
On this 2010 to 2015 Honda Civic with the 1.8 gas engine, P0977 points to the CVT shift solenoid valve B electrical circuit reading high at the ECM/PCM. The car may have transmission driveability complaints, abnormal CVT operation, or it may only have a warning light and a stored code. Broadly, we’re looking at possible power feed issues, wiring opens, the solenoid B circuit, the solenoid wire harness, or PCM-side control. One important point up front: this code is called out as an electrical circuit problem, not a mechanical failure inside the transmission. Before getting into pinpoint checks, start with the basic system checks and follow a structured diagnostic approach.
Verify the problem first
Start by verifying the fault. Turn the ignition ON, or use ON mode if it has the engine start/stop button. Clear the code with the HDS. Start the engine in Park and let it run for at least 10 seconds, then check for pending or confirmed codes with the HDS. If P0977 comes right back, the failure is duplicated and you move into circuit testing. If it does not come back, treat it as intermittent for now. When captured data is available, reproduce the captured conditions instead of guessing.
Check the feed fuse
With the ignition OFF, check fuse No. B7, the 15 A fuse in the under-dash fuse and relay box. If that fuse is OK, keep going down the diagnostic path. If it is not OK, replace the No. B7 15 A fuse. If it blows again, repair the short to ground on that fuse circuit before moving any farther.
Check the IG1_MISS_SOL power feed
Next, check the IG1_MISS_SOL line for an open. Jump the SCS line with the HDS, disconnect PCM connector A, the 51 pin connector, then turn the ignition ON. Measure voltage between PCM connector A terminal No. 1, the blue wire, and body ground. You’re looking for battery voltage on that feed. If battery voltage is present, the IG1_MISS_SOL wire is OK and the next step is the solenoid B side of the circuit. If battery voltage is missing, repair the open in the IG1_MISS_SOL wire between the PCM and the No. B7 15 A fuse in the under-dash fuse and relay box.
Check shift solenoid valve B operation
Now test shift solenoid valve B. This is the point where you separate a solenoid-side problem from the rest of the SOL_B control path. If shift solenoid valve B works properly, continue to the SOL_B wire continuity check. If shift solenoid valve B does not work properly, go to the resistance check at the solenoid itself.
Check the SOL_B wire for an open
For the SOL_B open-wire check, turn the ignition OFF, jump the SCS line with the HDS, then disconnect the solenoid wire harness 8 pin connector on the engine wire harness side and PCM connector B, the 51 pin connector. Check continuity between solenoid wire harness connector terminal No. 4, the green with white wire, and PCM connector B terminal No. 12, also green with white. If there is continuity, the SOL_B wire is OK. At that point, update the PCM if it does not have the latest software, or substitute a known-good PCM and recheck. If P0977 goes away after an update, the troubleshooting is complete. If it goes away with the substitute PCM, replace the original PCM. If there is no continuity, repair the open in the SOL_B wire between the solenoid wire harness and the PCM.
Check solenoid B resistance
If the solenoid operation check sent you to the solenoid itself, remove the solenoid wire harness and measure resistance between shift solenoid valve B 2 pin connector terminal No. 1 and terminal No. 2. The specification is 8.9－12.2 Ω. If the resistance is in that range, shift solenoid valve B is OK, and the directed repair is to replace the solenoid wire harness. If the resistance is not 8.9－12.2 Ω, shift solenoid valve B is faulty, and the directed repair is to replace the valve body.
Verify the repair
After any repair, update, substitution, or harness work in this path, keep verification separate from the pinpoint testing. Clear the code, reproduce the operating conditions, and confirm P0977 stays gone. The key is not to treat this like a mechanical CVT fault. Prove the feed, prove the SOL_B circuit, prove the solenoid measurement, and only then make the directed repair. For more diagnostic training, visit stepdiagnostics.com.
Final check
This code is often approached as an electrical diagnosis of the solenoid B circuit, not as a mechanical transmission teardown.
For more guided automotive diagnostics, visit STEP Diagnostics.
