P0977
Shift Solenoid B Control Circuit High
Powertrain Transmission Control Solenoid Circuit Voltage 🟡 Moderate — Fix within a week
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What This Actually Means
In plain language — no jargon

The transmission control module detected that Shift Solenoid B is receiving too much voltage, similar to a light switch stuck in the 'on' position. This prevents proper gear shifting because the solenoid can't be controlled correctly.

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Symptoms You May Notice
3 known symptoms for this code
Transmission stuck in limp mode or single gear
Harsh or delayed shifting between gears
Check Engine Light illuminated
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Embedded Systems Insight
What the ECU/ECM is actually computing

The ECM monitors the control voltage sent to Shift Solenoid B during transmission operation. It measures the circuit voltage to ensure it stays within safe operating range. When voltage exceeds the normal threshold, the ECM detects a high-voltage fault condition.

Voltage & Parameter Thresholds

Parameter Normal Range Fault Condition
Solenoid B Control Voltage 0-12V (typical PWM signal) Sustained voltage above 14.5V or open circuit detected
Current Draw 0.5-2.0 amps during actuation Excessive current or no current response
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Diagnostic & DIY Fix Guide
Check these in order — from cheapest to most complex
1
Battery terminals and connectors
Clean corrosion from battery terminals and solenoid connector contacts with a wire brush.
2
Solenoid B wiring harness
Inspect wires for damage, pinches, or exposed insulation that could cause shorts.
3
Shift Solenoid B
Replace the solenoid if wiring and connections test normal; internal failure is likely.