P0777 Code: Pressure Control Solenoid B Stuck On (GM 6L80/8L90)

P0777 is "Pressure Control Solenoid B Stuck On" in generic SAE terms. It is the opposite of P0776, and in some ways more dangerous. The transmission module has found that a clutch it wanted released is still holding. On GM's 6L80 and 6L90 that is the 3-5-Reverse clutch, controlled by what GM calls Clutch Pressure Control Solenoid 2. On the 8L90 and 8L45, GM's tables tie Pressure Control Solenoid B to clutch 2, the CB12345R clutch. A clutch that will not let go makes the transmission fight itself. And on early 2017 8-speed trucks, GM has a bulletin where the fix is software, not parts.

What Does P0777 Mean on a GM 6L80 or 8L90?

Every shift in these clutch-to-clutch transmissions is a handoff. One clutch releases (the "offgoing" clutch) while another applies (the "oncoming" clutch). Each clutch's pressure comes from its own variable pressure control solenoid. P0777 means the module commanded the solenoid B clutch to release, and the speed sensors showed it was still carrying torque.

Transmission	GM's name for it	Clutch	When that clutch should be released
6L80 / 6L90	Clutch Pressure Control Solenoid 2 Stuck On (OBD tables: Pressure Control Solenoid B Stuck On [C35R])	3-5-Reverse	1st, 2nd, 4th and 6th
8L90 / 8L45	Pressure Control Solenoid B Stuck On (clutch2/CB12345R)	CB12345R	6th, 7th and 8th

The 8L90 clutch names list the gears each element is applied in, so CB12345R is applied in 1st through 5th and Reverse. On an 8L90, a stuck-on fault shows up on the way into 6th and above. On a 6L80, it shows up in the gears between the 3-5-R gears.

Why "Stuck On" Means the Transmission Is Fighting Itself

A planetary automatic makes a gear by holding exactly two clutches on a 6L80 (three on an 8L90). Add one more applied clutch and you are asking the gearsets to be in two ratios at once. Something has to slip, and it is usually the clutch that is not supposed to be on.

On a 6L80, the 3-5-R clutch combined with the 1-2-3-4 clutch makes 3rd gear, and combined with the 4-5-6 clutch makes 5th gear. So if the 3-5-R clutch stays partly applied:

• in 1st or 2nd, the transmission is partly trying to be in 3rd,
• in 4th or 6th, it is partly trying to be in 5th.

The driver feels a bind, a harsh or "double" shift, or a sluggish truck that feels like it is dragging the brakes. The clutches involved make heat very fast.

There is one more 6L80 detail worth knowing. ATSG's technical guide says Clutch Pressure Control Solenoid 2 is normally high: with no current, it gives full pressure. So losing control of this solenoid tends to apply the 3-5-R clutch, which matches the 6L80's fail-safe of defaulting to 3rd or 5th. A solenoid or TCM that cannot control this circuit can therefore look exactly like "stuck on."

How Does the TCM Prove the Clutch Is Stuck On?

This is one of GM's cleverer monitors, and the logic tells you what is happening inside.

6L80/6L90 (GM 2011 OBD summary), steady-state test:

1. The truck is cruising in a steady gear (1st, 2nd, 4th or 6th) and the module sees 400 RPM or more of slip.
2. It runs an intrusive test: it exhausts one of the clutches that should be holding. In 1st it dumps the low/reverse clutch; in 2nd and 6th it dumps the 2-6 clutch; in 4th it dumps the 1-2-3-4 clutch.
3. Then it reads the ratio. If the transmission lands at about 1.46–1.61 (around 3rd, 1.53) or about 0.81–0.89 (around 5th, 0.85), then the 3-5-R clutch must still be applied, because nothing else could produce that ratio.
4. It counts a failure after about 1.1 seconds; the code sets after a set number of counts on one trip.

There is also a dynamic version that watches shifts. If the 3-5-R clutch is supposed to be exhausted but engine speed does not start to change as expected, the module counts that too.

8L90/8L45 (GM 2017 OBD summary): the monitor runs during automatic shifts. In the torque phase after the handoff, if slip stays at 40 RPM or less before any engine speed change, the offgoing CB12345R clutch has not released. The oncoming clutch is fighting it. Fail events are counted and the code sets on one trip.

For an owner, the practical meaning is that the TCM may deliberately drop a clutch while you are driving to run this test, and you may feel it. That is diagnosis, not a new failure.

The 8-Speed Bulletin Where the Fix Is Software

GM bulletin 16-NA-404, "Malfunction Indicator Lamp (MIL) Illuminated – DTC P0747, P0777, P0797, P2715 or P2724 May Be Set Current or History in Transmission Control Module," covers early-production 2017 vehicles with the 8L45 and 8L90: Silverado, Sierra, Tahoe, Suburban, Yukon, Escalade, Camaro, Corvette, ATS, CTS and CT6, each up to a start-of-production date in late 2016.

GM's stated cause: a calibration anomaly in the TCM. The fix:

• Reprogram the TCM with the latest software through SPS.
• Keep battery voltage between 12.6 and 15.5 volts during programming with an approved battery maintainer.
• Then run Transmission Control Module Setup / Service Fast Learn.

If you own an early 2017 8-speed truck with P0777, ask the dealer to check this bulletin before anyone quotes a valve body. A dealer can confirm in minutes whether your TCM already has the update.

P0777 on the 6L80 vs the 8L90

Item	6L80 / 6L90	8L90 / 8L45
Clutch that will not release	3-5-Reverse	CB12345R
Where the bind appears	1st, 2nd, 4th, 6th and the shifts between them	5-6 upshift and 6th–8th; downshifts back into the low gears
TCM	Inside the transmission (TEHCM)	External T87 TCM; solenoids in the valve body
Known software fix	None found for P0777	16-NA-404 (early 2017 production)
Hardware repair	TEHCM or valve body repair, programmed and relearned	Valve body / solenoids, with a TCM update for the new solenoid data
Fluid	DEXRON VI	Mobil 1 Synthetic LV ATF HP on vehicles serviced under 18-NA-355

Is P0777 Electrical or Hydraulic?

It can be either, and the three possibilities need different fixes.

• Software. On early 2017 8-speed trucks, GM documents a calibration cause (16-NA-404).
• Electrical control. The circuit codes for this solenoid are P0966/P0967 on the 6L80 (per ATSG) and P0964/P0966/P0967 on the 8-speed (per GM's tables). If any are present, fix them first. On the 6L80's normally-high solenoid, losing control means pressure goes up, not down.
• Hydraulic. A regulator valve stuck in the apply position, debris at the solenoid's exhaust, or a clutch whose piston does not fully retract. These leave the circuit codes clear but still set P0777.

Debris is a common link. GM's PI1393 for 2015 6L80/6L90 trucks warns that torque converter clutch material can pass through the pump and damage it. Material in the fluid can hold a valve or solenoid in the wrong position. See our P0741 guide.

Programming and Relearn: Don't Skip It

For P0777, the programming step is often the repair itself, and it matters for any hardware fix too.

• 8L90/8L45: GM's bulletins direct technicians to program the TCM through SPS and then run Service Fast Learn. GM's 15-07-30-002 explains that the scan tool will not start Fast Learn unless transmission fluid is between 75°C and 85°C (167–185°F), and warns that skipping it can cause poor transmission performance and DTCs. If the valve body or solenoids are replaced, the TCM also needs the new solenoid data; Gears Magazine explains that the TCM uses a part-unique number built from the solenoid serial numbers.
• 6L80/6L90: a replacement TEHCM must be programmed to the VIN and calibration, then relearned. Rebuilders warn that skipping it can cause limp mode, flare or bind, and faster clutch wear. That is a particular problem here, because bind is already the symptom.

Either way, keep the battery supported during programming. Our P0562 guide covers why voltage matters to modules.

Codes Commonly Seen With P0777

Code	Description	What it suggests
P0777	Pressure Control Solenoid B Stuck On	The fault itself
P0776	Same solenoid Stuck Off	A sticking valve that sometimes applies and sometimes hangs
P0747 / P0797 / P2715 / P2724 (8-speed)	Other pressure control solenoid stuck-on codes	Several together on an early 2017 8-speed point strongly at 16-NA-404
P0966 / P0967 (and P0964 on 8-speed)	Solenoid circuit codes	Electrical. Diagnose first
P0731 / P0732 / P0734 / P0729 (6L80)	Incorrect 1st / 2nd / 4th / 6th ratio	The gears where a stuck 3-5-R clutch drags
P0716 / P0717 / P0722	Speed sensor faults	Block the monitor. Fix first
P0700	MIL request	The notification

Symptoms of P0777

• Bind or "tie-up" feel: the truck feels like it is dragging, or surges and bogs
• Harsh, double-bump or stacked shifts, especially where the solenoid B clutch should release (6L80: 3-4 and 5-6; 8L90: 5-6)
• Possible momentary shifts you did not expect while the TCM runs its intrusive test
• Check engine light on the first failure, often with P0700
• Default or limited-gear operation; on a 6L80 this often means 3rd or 5th
• Rising transmission temperature and a hot or burnt fluid smell

On urgency: treat P0777 as more urgent than P0776. A slipping clutch wears itself out. A clutch that will not release damages both clutches in the fight, and the heat reaches the fluid and valve body. Drive only to get it diagnosed, do not tow, and watch transmission temperature if your truck displays it.

Causes and How to Confirm Each

Cause	How to confirm it	Notes
TCM calibration anomaly (early 2017 8L45/8L90)	Dealer VIN check against 16-NA-404; software version	Fix is reprogramming plus Service Fast Learn
Regulator valve stuck in the apply position	Valve body removal and inspection	6L80: 3-5-R clutch regulator. Common hydraulic cause
Debris at the solenoid or valve	Pan, filter and valve body inspection	Find the source, such as converter material (PI1393)
Solenoid not exhausting / not controlling	GM solenoid performance test; circuit codes	6L80: TEHCM. 8L90: valve body/solenoid plus TCM update
Missed relearn after a repair	Ask whether Service Fast Learn or adapts were run	Cheap to correct. Rule it out before buying parts
Clutch piston not retracting or clutch damage	Teardown; multiple ratio codes	Overhaul territory
Wrong or misassembled valve body after a rebuild	Verify parts and installation	Sonnax warns that separator plate mismatches and reversed clutch select springs cause major faults

How Is P0777 Diagnosed?

1. Read all TCM codes and freeze frame. Several "stuck on" codes together on an 8-speed is a strong clue.
2. Identify the transmission and model year. Early 2017 8L45/8L90? Check 16-NA-404 first.
3. Check TCM software against the latest calibration and ask whether a relearn was done after any recent repair.
4. Clear circuit and speed sensor codes first.
5. Check fluid level and condition with GM's procedure.
6. Road test with a scan tool, watching commanded gear, ratio and slip across the shifts where solenoid B's clutch should release.
7. Pan down and inspect for debris.
8. Remove and inspect the valve body, test the solenoid, and check the regulator valve for sticking.
9. Repair what is confirmed, then program and run Service Fast Learn or adapts as required.
10. Road test through full upshift and downshift sequences to confirm there is no bind.

Parts and Cost

Repair	What it involves	Cost picture (estimates)
TCM reprogramming + Service Fast Learn	16-NA-404 on early 2017 8-speed trucks	Lowest hardware cost; labor only, and may be covered by warranty
Relearn after a prior repair	Scan-tool procedure	Low
Valve body repair	Sticking regulator valve or debris	Mid-range
6L80 TEHCM	Confirmed solenoid/TCM fault; programmed and relearned	Substantial
8L90 valve body / solenoids	Plus TCM update for the new solenoid data	Substantial
Overhaul	Clutch damage from a prolonged tie-up	Highest

These are general cost ranges, not quotes. Confirm parts by VIN and RPO, and ask about powertrain coverage first.

What Other P0777 Pages Get Wrong

• Treating stuck on like stuck off. They are opposite failures. P0776 is slip; P0777 is a clutch that will not release, which is a tie-up and more urgent.
• Not naming the clutch. The 3-5-R clutch on the 6L80 and CB12345R on the 8L90. That tells you which shifts to watch.
• Missing the software bulletin. On early 2017 8L45/8L90 vehicles, GM's 16-NA-404 fix is reprogramming.
• Replacing parts without a relearn. GM warns that skipping Service Fast Learn can cause DTCs and poor performance.
• Assuming a dead solenoid releases the clutch. The 6L80's solenoid 2 is normally high, so losing control tends to apply the clutch.
• Quoting a rebuild first. Software, relearn and valve body causes come before clutches, unless the fluid and teardown say otherwise.

A Note on Sourcing for This Code

Read directly by us: GM bulletins 16-NA-404 and 15-07-30-002 (8-speed programming and Service Fast Learn), PI1393 (converter debris), 18-NA-355 (8-speed fluid), GM's 2011 OBD summary tables for the 6L80/6L90 and 2017 OBD summary tables for the 8-speed controller (monitor logic, clutch names, ratio windows), and ATSG's 6L80 technical guide (solenoid type and fail-safe). Rebuilder material (Gears Magazine, Monster Transmission, Sonnax) is reported and corroborated. We found no 6L80-specific GM bulletin for P0777. Ratio windows and timers are calibration values for the years shown. Have a dealer check your VIN for current bulletins and software.

Frequently Asked Questions

What does P0777 mean on a 6L80 truck?

Clutch Pressure Control Solenoid 2 Stuck On. The 3-5-Reverse clutch did not release when it should have. The TCM confirms this by dropping another clutch and seeing the transmission land in a 3rd- or 5th-gear ratio.

What does P0777 mean on an 8L90?

Pressure Control Solenoid B Stuck On for clutch 2, the CB12345R clutch. That clutch should release for 6th, 7th and 8th. If it does not, the module sees too little slip during the shift and sets the code.

Can a software update fix P0777?

On early-production 2017 8L45 and 8L90 vehicles, yes: GM bulletin 16-NA-404 blames a TCM calibration anomaly and calls for reprogramming followed by Service Fast Learn. For other vehicles, it is worth asking whether newer software exists, but do not assume it will fix a hardware fault.

Is P0777 worse than P0776?

Usually, yes. P0776 is a clutch that slips. P0777 is a clutch that stays applied when another is applying, so two clutches fight and build heat quickly.

Why does my truck feel like it's dragging or binding?

A clutch that should be released is still holding, so the gearsets are being pushed toward two ratios at once. On a 6L80 it feels like part-3rd or part-5th; on an 8L90 you feel it most on the shift into 6th.

Do I need a relearn after the repair?

Yes. On the 8-speed, GM requires Service Fast Learn after programming, with fluid between 75°C and 85°C. On a 6L80, a new TEHCM must be programmed and the adapts relearned.

Can I drive with P0777?

Only to get it diagnosed. A tie-up generates heat quickly and can damage two clutches at once. Do not tow.

I have P0777 with several other "stuck on" codes. What does that mean?

On an early 2017 8-speed truck, P0747, P0777, P0797, P2715 and P2724 together match GM bulletin 16-NA-404, a calibration issue. On other vehicles, several solenoid codes at once suggest a shared cause, such as debris, fluid or the valve body, rather than several failed solenoids.

Sources We Checked

GM documents and industry references used for this guide. Calibrations and thresholds vary by model year — confirm against current GM service information for your VIN.

• GM OBD system operation summary (transmission diagnostics)
• GM service bulletin (NHTSA copy)
• GM service bulletin (NHTSA copy)
• GM service bulletin (NHTSA copy)

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