P0977 Code: Test Shift Solenoid B Control Circuit High
P0977: Map and Load-Test the Control Circuit
Identify the exact transmission and separate a high electrical circuit from hydraulic or mechanical shift complaints.
DIAGNOSTIC FOCUS
- FAULT TYPE
- a high electrical condition in the OEM-defined shift-solenoid B control path
- FIRST CHECKS
- Exact component identity, loaded electrical integrity, selected/actual gear, turbine and output speed, temperature, solenoid command/current and voltage, and companion-code order
Solenoid letters and driver polarity vary by transmission; “high” does not identify a universal valve or high fluid pressure.
P0977 means Shift Solenoid “B” Control Circuit High. The transmission controller detected voltage, current, or diagnostic feedback above the expected range on the control path assigned to shift solenoid B.
Confirm the exact gearbox and full OEM description before testing because a feed-side, low-side, smart-driver, or internal-harness design changes the expected reading. Save the complete scan and freeze-frame record before clearing anything, then use the exact VIN service information to identify the monitored circuit and approved test points.
What Does the P0977 Code Mean?
P0977 is the diagnostic label for Shift Solenoid “B” Control Circuit High. Shift solenoid B is a software and hydraulic assignment, not a universal physical location across transmissions. It is a monitor result, not a parts order, and it does not by itself prove the solenoid, valve body, transmission controller, or entire transmission is defective.
A high direction may indicate an open low-side path, short to power, weak terminal, abnormal coil load, internal harness fault, or controller protection depending on driver design. The useful distinction is between an external feed/control fault, an internal harness or solenoid load, and a hydraulic or mechanical shift problem that does not explain the high circuit by itself. That distinction determines whether the next test belongs at a connector, a power or ground path, a control signal, a hydraulic or mechanical system, or an operating-condition check.
Gear, speed, temperature, current, and companion solenoid codes help determine whether the electrical event came first or a shift-performance code is secondary. A scan tool cannot replace the current wiring diagram, connector view, service precautions, and approved test method. Do not import limits or component locations from another model year.
Capture confirmed, pending and history codes, freeze frame, first-failure order, system voltage, and the conditions present when P0977 set.
Identify transmission family, solenoid B assignment, shared supply, driver polarity, external connector, internal harness, controller pins, fluid procedure, and serviceability.
Load-test the assigned feed and control path, compare commanded current with gear/speed response, and isolate internal from external wiring in the OEM order.
P0977 Symptoms, Severity, and Driving Safety
The controller may request a warning and store the event.
The assigned clutch event may not occur as scheduled.
Selected and achieved gear can disagree.
A fixed gear or torque limit may protect the unit.
An internal connection or coil can fail only at temperature.
A pending electrical event may be captured before a repeatable symptom.
Treat P0977 as a transmission-control concern needing prompt diagnosis. Continued slip, harsh engagement, overheating, or loss of drive can create additional damage and traffic risk.
P0977 Causes and the Evidence That Separates Them
A sound P0977 diagnosis must fit the stored conditions and companion codes. Shared feeds and driver polarity should be mapped before resistance testing because identical meter readings can mean different things on different designs.
Open or High-Resistance Control Path
An open low-side driver path or poor terminal can remain electrically high.
How to prove it: Use loaded voltage and current evidence at approved points rather than continuity alone.
Check firstShort to Power
Harness damage, fluid intrusion, or crossed wiring can force the control circuit high.
How to prove it: Isolate external and internal sections using the OEM connector sequence.
Check firstShared Feed or Connector Fault
A relay, fuse output, splice, or transmission connector can affect several solenoids.
How to prove it: Compare companion solenoid codes and voltage drop under command.
Verify directlyInternal Harness or Solenoid Load
Heat, fluid, a coil fault, or weak internal terminal can alter current.
How to prove it: Test at specified temperature and connector state; do not apply a universal resistance value.
Verify directlyController Driver Protection or Failure
The controller may disable a path when it detects an abnormal load, or the output stage may fail.
How to prove it: Prove powers, grounds, wiring, and load before programming or controller replacement.
Verify directlySeparate Hydraulic or Mechanical Fault
A sticking valve, pressure loss, or clutch problem can coexist with the circuit fault.
How to prove it: Resolve P0977 electrical evidence first, then follow remaining ratio/pressure diagnostics.
Final branchKeep P0977 separate from P0976 circuit low, P0756 performance/stuck off, and P0757 stuck on. Test the failed state when possible, document the result, and replace a part only after measured evidence supports it.
Using MA500 as an Electrical Baseline for P0977
The iCARZONE MA500 12V/24V Battery & Charging System Tester with SOH/SOC checks battery SOH/SOC, internal resistance, ripple, cranking, and 12V/24V charging. Use it only to document supply stability during P0977 diagnosis.
MA500 does not read or clear engine fault codes. It provides no freeze frame, ECU live data, or actuator commands. Use separate scan equipment and VIN-specific service information.
Electrical tests require the exact transmission pinout and approved adapters. Fluid checks require the specified temperature and level method; internal work demands cleanliness and safe lifting. Its battery results cannot identify the shift-solenoid B control circuit or replace the specified loaded test.
iCARZONE MA500 12V/24V Battery & Charging System Tester with SOH/SOC
Use MA500 only to document the battery, cranking and charging baseline. A separate scan tool and OEM procedure are required to read P0977, capture shift event, gear and speed data, temperature, solenoid commands, voltage and companion codes, and prove the fault.
Checked September 4, 2026: the public page showed $32.99 USD, no compare-at price, and available status. Recheck the offer, stock, and compatibility.
How to Diagnose P0977 in 6 Evidence-Based Steps
Use this order to preserve the event and avoid parts guesses. Review whether other solenoids share the same high direction; a group pattern can identify one feed, connector, or ground issue. Let each result choose the next OEM test.
P0977 Quick Diagnostic Path
-
1
Save the Complete Event
- Record code status, freeze frame, selected/actual gear, turbine and output speed, temperature, solenoid command/current and voltage, voltage, and first-failure order.
- Note companion supply, reference, communication, or performance faults.
-
2
Confirm the Exact Hardware
- Use the VIN to identify shift-solenoid B control circuit, its controller, connectors, shared paths, and enable conditions.
- Do not borrow terminals, limits, or locations from another application.
-
3
Inspect the Accessible Path
- Safely inspect locks, seals, corrosion, routing, heat or fluid exposure, grounds, and prior repairs.
- Preserve the failed state; do not pierce seals or spread terminals.
-
4
Compare Command and Result
- Observe selected/actual gear, turbine and output speed, temperature, solenoid command/current and voltage during a safe reproduction of the stored shift and temperature condition.
- Scan data narrows the branch but does not replace the specified physical test.
-
5
Test the Leading Branch
- Follow the OEM order for loaded power, ground, signal, control, continuity, isolation, and system tests.
- Record each result and prove external wiring before parts.
-
6
Repair and Verify
- Correct only the proven circuit, component, mechanical, or applicable calibration fault.
- Restore all disturbed items, run the specified monitor, and rescan.
How to Fix P0977 and Verify the Repair
Repair Feed or Control Wiring
Restore the exact fuse cause, splice, terminal, ground, or conductor that failed loaded testing.
Replace a Proven Internal Harness
Use clean procedures and correct seals only when evidence locates the fault inside the transmission.
Replace the Proven Solenoid
Follow gearbox-specific serviceability, fluid, and adaptation rules after load tests support failure.
Service the Driver or Remaining Hydraulic Fault
Pursue controller or valve-body work only after its separate evidence is complete.
Evidence Capture and Mapping
VIN-specific quoteDiagnosis begins with a complete scan, exact hardware identification, and the current service procedure.
Connector or Harness Repair
VIN-specific quoteAccess, sealed terminals, corrosion, heat damage, and shared splices determine labor.
Component Replacement
VIN-specific quoteParts cost alone is incomplete; access, seals, fluids, setup, and relearn can matter.
Controller or Complex System Work
VIN-specific quoteProgramming, network, internal mechanical, or high-risk procedures need separate proof and estimating.
Record the proven fault and repair. Verify normal loaded circuit behavior, correct gear changes, no abnormal slip or harshness, completed adaptation, and no returning solenoid or ratio code.
Clear codes after repair, run the specified monitor or road test, and rescan every relevant module. A short idle without the warning is not enough.
P0977 OEM Differences and DIY Limits
Solenoid letters, feed/driver polarity, internal harness layout, current limits, and serviceability vary across transmissions. Match the OEM description, diagram, terminals, test conditions, and bulletins to the full VIN.
Which transmission is installed and what shift element does its solenoid B control?
Does high mean open control, short to power, abnormal load, or an OEM sub-fault?
Does access require fluid-temperature control, pan removal, adaptation, or programming?
Some units allow separate solenoid replacement; others require a calibrated valve body or mechatronic assembly and adaptation. Stop before unverified probing, programming, hazardous work, or disassembly requiring special tools.
- Save all modules, freeze frame, and fault order.
- Inspect accessible wiring and connectors only after make the vehicle safe and follow the oem precautions before physical testing.
- Inspect accessible connectors with power off.
- Use the correct diagram and approved probes.
- Do not bypass protection, power a component directly, or work around uncontrolled pressure, heat, fuel, exhaust, or moving parts.
- Do not pierce seals or spread terminals.
- Do not run unsupported commands or programming.
- Escalate for special tools, disassembly, or controlled hazards.
Frequently Asked Questions About P0977
Does P0977 prove shift solenoid B is bad?
What does “circuit high” mean?
Can I keep driving with P0977?
Can a weak battery affect P0977?
Can MA500 diagnose P0977?
Is a continuity or resistance check enough?
Should I clear the code before testing?
How is the repair verified?
Sources and Technical Review Notes
- Hino Aisin Transmission DTC Bulletin — Lists P0977 as shift solenoid 2 system failure high and shows circuit testing in that application.
- Subaru TR580 Transmission Bulletin — Defines P0977 as Shift Solenoid B Control Circuit High and documents a limited connector/condensation condition for specified models.
0 comments