10L80 P0748: Pressure Control Solenoid Electrical Causes and Fix

P0748 puts a lot of good 10L80 valve bodies in the trash for no reason. The code has the word "solenoid" in it, the truck shifts badly, and the pan comes off before anybody load-tests a battery. On a GM 10-speed that is backwards. P0748 is a circuit code, not a performance code, and the thing it is complaining about is electrical current, not oil pressure.

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What GM's own naming tells you about P0748

The 10L80 does not use one master "pressure control solenoid." It uses six clutch-control solenoids plus a line pressure solenoid, a TCC solenoid, and a default disable solenoid. GM numbers the clutch solenoids and gives each one its own trio of codes: stuck off, stuck on, and control circuit.

You can see the naming convention straight out of a factory bulletin. GM bulletin 22-NA-258, covering a no-reverse complaint on 2021–2023 Silverado, Sierra, Tahoe, Suburban, Yukon and Escalade models, lists its codes as "P0776: Transmission Control Solenoid Valve 2 Stuck Off" and "P2732: Transmission Control Solenoid Valve 6 Stuck Off." Same pattern, one solenoid down:

Generic scan tools print P0748 with its SAE label, "Pressure Control Solenoid A Electrical." That word electrical is the whole diagnosis. The TCM is not reporting that a clutch slipped. It is reporting that when it commanded a current through that winding, the current it measured coming back was outside the window it expects — open, shorted, or high-resistance somewhere in the loop.

Why you cannot ohm-test your way out of this

The solenoid on the other end of that circuit is not the part you grew up with. Per Sonnax, 10-speed valve bodies use casting-integrated direct-acting solenoids, held into the casting with retainer clips, working directly on the clutch control valve. No fluid passes through them — they only produce clutch pressure with current, which is why a 10-speed will not move at all unplugged.

Sonnax's Jim Dial describes the mechanism precisely: the 10-speed family uses a linear-force solenoid with an individual pin that contacts the regulating valve to control valve position and clutch regulation. On Gen. 1 units that regulated pressure feeds a latch valve between spools B and C; because spool C is larger than B, the valve strokes and regulates apply pressure through a narrow passage until inlet pressure overcomes the spring and pins the valve, connecting full line pressure to the clutch.

Transmission Digest's Mike Souza documents the electrical side that kills resistance testing as a pass/fail: every control solenoid valve is flow-tested after assembly at specific electrical values, sweeping current up and then back down. Those current-versus-pressure data points are saved to a file, the file number is marked on the solenoid housing end or on the valve body, and that data gets programmed into the TCM. Two solenoids with identical resistance can be calibrated differently.

ATRA's GEARS teardown of the 10L series adds the parts-counter reality: as of publication the linear pintle solenoids were not sold separately, so you order a valve body and program the supplied Part Unique Number (PUN) or Mechanical Characterization and Virtual Matching (MCVM) number. A donor solenoid can be used, but the band number has to match the original.

Resistance tells you whether a winding is open or dead-shorted. It does not tell you the solenoid is good, and it does not tell you the solenoid is right for that TCM.

Diagnose P0748 in this order

1. Batteries and system voltage, before anything else

This is the step that gets skipped and it is the one that most often owns the code. Sonnax's Jim Mobley put it in print for exactly these units: a common issue on 10-speed work trucks is that the battery needs a charge after the vehicle has sat in the shop a few days, and after repair the unit acts like it is not adapting — harsh engagements, erratic upshifts and downshifts — while the rebuilder starts thinking valve body. Drive it to temperature and it behaves. Batteries in both Fords and GMs last about three years.

A current-monitored solenoid driver is exactly the circuit that a weak battery or a bad ground upsets first. GM says the same thing from the other direction in 22-NA-258: stable battery voltage is critical, and any fluctuation, spiking, over-voltage or loss of voltage will interrupt TCM programming. Load-test every battery on the truck (diesels and many work trucks have two) and check the TCM grounds before you touch the pan.

2. Read every module, not just the TCM

Per GEARS, shift strategy on this unit is altered by codes stored elsewhere, and GM's own procedures do not always draw the line for you. Their example: chassis code C0267 (low brake fluid level) causes no upshifts in Tow/Haul mode, and the truck shifts correctly with Tow/Haul off. P175E (transmission control system, shift limiting active) means the TCM has already put its own pressure and shift protection strategy in play because of sensor data. Deal with the surrounding codes first or you will chase a symptom the TCM created on purpose.

3. Wiggle the connector, then measure at the TCM

With the engine running and the code current, back-probe the solenoid circuit at the transmission case connector and flex the harness. A P0748 that comes and goes with harness movement is a pass-through connector or an internal solenoid-body lead, not a coil. Compare commanded current to actual current on the scan tool while you command the solenoid with bidirectional controls. One thing that trips people up here: the line pressure and TCC solenoid currents never truly go to zero when commanded off, because an idle current is maintained for feedback and back-EMF suppression, so a small non-zero reading on a solenoid you commanded off is normal rather than a stuck driver.

4. Only then pull the pan

When you get in there, inspect two things Sonnax calls out specifically. First, the solenoid retainer clips — the heavy direct-acting solenoids need to be examined for bore tightness, and Sonnax sells solenoid stabilization retainer 105740-19K to hold them and prevent spring retainer collapse. Second, the separator plate: impregnated plate filters come loose and cause valves to stick. GEARS adds the LPC accumulator bore and linear pintle solenoid bore areas to the inspection list, and notes that wear in those areas means the valve body gets replaced, not repaired.

Do not confuse P0748 with P0747 — that one is a recall

P0747 is the stuck-on sibling, and on Gen. 2 10-speeds it has a known mechanical cause that has nothing to do with wiring. In March 2025 GM issued Safety Recall N242480630 for the 10L1000 and Gen. 2 10L60, 10L80 and 10L90, covering a momentary wheel lock-up at higher speeds that can include a downshift back to 2nd gear. Sonnax traced it to wear in the feed limit low valve, which does double duty: it sits in the boost-ball clutch-regulating circuit and also limits solenoid feed to the default disable (DD) solenoid.

The DD solenoid is powered on at all times and does not drop out until a default event. When feed pressure to it falls off, the default enable and default select valves route line pressure into the exhaust backfill circuit, applying clutches through the exhaust ports — which is 2nd gear, and which is why the drive wheels can try to lock. Sonnax reports feed limit low wear as early as 35,000 miles on tow-duty units, says the code you will see is P0747 (the E clutch reading on when it should be off), and notes the recall software puts the transmission in 5th gear and lights the MIL when the TCM detects the wear starting.

Government filings back the scope. NHTSA campaign 24V797000 covers 2020–2022 diesel Silverado and Sierra plus 2021 full-size SUVs for a transmission control valve that may fail and lock the rear wheels. 26V085000 (GM number N252536750) covers 43,743 additional 2022 Tahoe, Suburban, Yukon, Yukon XL and Escalade models with the 10-speed and ETRS. 26V083000 re-recalls vehicles that were repaired incorrectly under 24V797. If a customer's 10L80 sets P0747 and drops to 2nd, run the VIN before you quote a rebuild.

The fix, with real numbers

• Circuit fault: repair the harness, connector, or ground. Nothing comes off the truck.
• Solenoid or valve body: GM's causal part in 22-NA-258 is control valve body assembly 24047996, with aux transmission seal 24047734, fluid pump seal 15035747 and exhaust manifold pipe seal 15077362 listed as supporting parts.
• Programming is mandatory, not optional. Per Transmission Digest, the TCM must be programmed with new or existing solenoid performance data after replacing the transmission assembly, the lower control valve body with solenoids, the TCM, or one or more solenoids.
• Fluid: DEXRON ULV, GM part 19352619 (U.S.) or 19352620 (Canada). GM TechLink's 2025 capacity chart lists the 10L80 fluid-change capacity at 7.7 L / 8.1 qt across RPO MQB, MQC, MHT, MI2, MHS and MHU. The 10L1000 in the HD trucks takes 13.6 L / 14.4 qt. Do not substitute an LV fluid in a ULV unit.
• Time: GM's own bulletin labor operation 8486228, "Diagnosing and Testing 10L80 Automatic Transmissions," is 2.6 hr. That is the benchmark to quote against, not thirty minutes and a parts cannon.

Keeping it from coming back

Two things are worth qualifying with the customer before you sell any of this. First, per GEARS, a harsh first engagement after the truck has sat is often catalytic converter light-off (CLO), not a defect: if engine coolant temperature is below 158°F (70°C) at start-up, the ECM raises idle, retards timing and adds injector pulses for 25 to 90 seconds. Drop it into gear during that window and the engagement will be harsh on any generation of this unit. Second, cold weather has its own path to solenoid codes — 22-NA-258 documents that an 8-hour cold soak at −25°C (−13°F) or colder can tear a spacer-plate screen and stick a valve, and GM notes the resulting codes may not appear until months later, with torn screens turning up on valve bodies replaced in the summer.

On the bench, replace the rotating sealing rings, hold clutch clearance to spec, and do not block the cooler bypass valve in full-flow mode — per GEARS, running the unit below the temperature range allotted for adaptive learning causes harsh or binding shifts all by itself.

FAQ

Is P0748 on a 10L80 always a bad solenoid?

No. P0748 is a control-circuit code, which means the TCM saw commanded current and measured current disagree. That happens with a failing battery, a corroded case connector, a bad ground or a TCM driver just as readily as with an open winding. Sonnax specifically documents 10-speed work trucks acting like they have valve body problems when the real fault is a battery near the end of its roughly three-year life.

Can I just replace the one solenoid?

Sometimes, but not casually. ATRA reports the linear pintle solenoids have not been available separately, so the OEM path is a valve body plus programming the supplied PUN or MCVM number. If you use a donor solenoid, the band number must match the one you removed, and the TCM still has to be programmed with the solenoid performance data afterward.

Can I drive with P0748?

Briefly and gently, at most. The TCM may already be limiting shifts and raising pressure to protect the unit. If the actual complaint turns out to be the P0747 feed-limit-valve pattern instead, Sonnax warns that extended driving in that condition will destroy clutch packs because the unit binds up. Get it diagnosed rather than driven.

What fluid does a 10L80 take, and how much?

DEXRON ULV only, GM part 19352619 in the U.S. and 19352620 in Canada. GM TechLink's 2025 chart lists 7.7 L / 8.1 qt for a 10L80 fluid change. An ultra-low-viscosity unit filled with LV fluid will give you shift quality complaints that look electrical and are not.

Does the 10-speed recall apply to my truck if it set P0747?

Check the VIN. NHTSA campaigns 24V797000, 26V083000 and 26V085000 all cover a transmission control valve that can fail and lock the rear wheels on GM 10-speeds, and the remedy is dealer-installed TCM software at no charge. That does not remove the worn valve, but it does change who pays for the diagnosis.