4L60E P0973: What "Shift Solenoid A Control Circuit Low" Means and How to Fix It

Your 4L60E-equipped GM truck, van, or car threw a check engine light, the scan tool says P0973, and the transmission is no longer shifting through all four gears. Before you drop the pan and start buying parts, understand what this code is actually telling you: P0973 is defined as Shift Solenoid "A" Control Circuit Low, and it is set by the transmission control module when it sees the voltage on that solenoid's control circuit fall outside the expected operating range (RepairPal).

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4L60E 1-2 & 2-3 A & B Shift Solenoid Set OEM 24230298

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That is an electrical complaint about a circuit, not a verdict on the solenoid. The single most common mistake on this code is replacing the shift solenoid when the real fault is damaged wiring, a contaminated connector, or fluid condition (YourMechanic). This article walks the circuit the way a transmission diagnostician does.

Symptoms of P0973 on a 4L60E

• Check engine light on, with the transmission stuck in a reduced number of gears
• Commanded gear on the scan tool does not match the actual gear ratio
• Difficulty or inability to shift into certain gears, harsh shifting, and uneven acceleration (YourMechanic)
• Increased fuel consumption (RepairPal)

Why losing solenoid A costs you two gears

On a 4L60E, shift solenoid "A" (the 1-2 shift solenoid) and shift solenoid "B" (the 2-3 shift solenoid) work together as simple on/off binary logic. Sonnax documents the states directly: commanding third gear turns both A and B off, commanding fourth turns only A on, and commanding second turns only B on (Sonnax, "4L60-E Flares on 2-3 Shift"). First gear is the remaining state, with both solenoids energized.

Follow that table and the consequence is obvious. Two of the four gear states require solenoid A to be on. If the A control circuit cannot pull the solenoid on, those two states are unreachable and the transmission is left operating out of the states that need A off. That is why a circuit fault on one small solenoid changes the whole shift pattern rather than just softening one shift.

Related GM-specific codes worth pulling

P0973 is the generic OBD-II wording. GM applications running a 4L60E also define their own codes on the same circuit, and pulling all of them narrows the fault fast. The Transmission Rebuilders Network lists, for this unit, P0751 (1-2 Shift Solenoid Valve Performance), P0753 (1-2 Shift Solenoid Circuit), P1751 (Shift Solenoid A Performance), P1842 (1-2 Shift Solenoid Circuit Low Voltage), and P1843 (1-2 Shift Solenoid Circuit High Voltage) (TRNW). A low-voltage code sitting alongside a performance code points somewhere very different than a low-voltage code sitting alone. If you are chasing the electrical side of solenoid A, our companion write-up on P0753 shift solenoid A electrical faults covers the same circuit from the GM code angle, and the 4L60E common failure codes guide maps how these codes cluster.

Diagnosis: test the circuit, not the part

1. Fluid level and condition first

Low or dirty transmission fluid is a listed cause of P0973 on its own (YourMechanic), and it is free to check. Do this before any meter comes out.

2. Know the circuit before you probe it

On the 4L60E application documented by Transmission Digest, both shift solenoids are fed power from the cluster fuse and are switched by low-side drivers in the PCM — the computer supplies ground, not power. On that 2001 S-10, the technician tested the whole circuit at PCM connector C2, terminals 51 and 52 (Transmission Digest, Gordon Kehler, January 2023). Pull the schematic for your specific year and application rather than assuming pin numbers carry over.

3. Do not trust a key-on voltage reading

This is the trap that sends good solenoids to the trash. With key on and engine off, that same technician measured 13V on each solenoid circuit, matching battery voltage — and noted explicitly that with no load on the circuit, full voltage only confirms the circuit is complete and will not reveal a resistance problem (Transmission Digest). A corroded splice can read 13V unloaded and still collapse the instant the solenoid draws current.

4. Load-test with an ammeter and Ohm's Law

The Sonnax TASC Force method is the fastest way to test the entire path — power distribution, ignition switch, external and internal wiring, the solenoid, the computer, and the computer grounds — without raising the hood. Pull the transmission fuse, put your ammeter leads in place of the fuse, then use a bi-directional scan tool to command each solenoid on and read the current draw. As a benchmark, a 24-ohm solenoid draws about one half amp, and a 12-ohm solenoid draws about one amp; divide your exact measured voltage by measured amps to get true circuit resistance (Gregg Nader, Sonnax, "Load-Testing Solenoid Circuits"). Resistance testing alone misses circuits that check fine unloaded and fail under load.

5. Compare against the published spec

GM's diagnosis charts for this unit give a shift solenoid resistance specification of 19-31 ohms. In the case study above, the 1-2 (solenoid A) control circuit drew 0.49 amps, which calculated to 26.5 ohms, and the 2-3 circuit calculated to 27 ohms — both comfortably in spec (Transmission Digest). Readings inside that window mean the solenoid and its wiring are not your problem, and a new solenoid will not clear the code.

6. When everything passes, suspect the driver

Both Sonnax and Transmission Digest document 4L60E complaints caused by the computer itself. The PCM's solenoid outputs are solid-state drivers with no physical contacts, and they can degrade rather than fail outright. In the Transmission Digest case, a lab scope on the low-side driver showed the circuit cycling 13V to 0V, but the turn-off transition took 15 to 27 seconds instead of being crisp — enough to delay the shift by 20 to 25 seconds. Replacing and programming the PCM fixed it (Transmission Digest). Sonnax reports the same class of fault causing a 2-3 flare with no codes at all, where the solenoid current dropped to zero slowly instead of instantly (Sonnax). Condemn the computer only after the circuit tests clean under load.

The fix: what to replace and why

If your load test lands outside the 19-31 ohm window, the shift solenoid or its harness leg is the fault, and it comes out with the pan and filter. The 4L60E's shift solenoids are inexpensive relative to the labor of getting to them, and A and B are identical in function within the binary logic described above — which is why they are sold and replaced as a pair. Replacing only the one that set the code leaves the other original solenoid, of identical age and heat history, sitting an inch away.

Pick by year: the 4L60E Shift Solenoid Kit for 1998-2009 covers the bulk of late 4L60E applications, and the 4L60E Shift Solenoid Kit with Filter bundles the filter you have to pull anyway. Everything for this unit is in our transmission solenoids collection.

Replace while you are in there

The pan is already down and the fluid is already out, so the marginal cost of these is close to zero:

• Filter and pan gasket — mandatory on any pan-down job. Our 4L60E filter kit with pan gasket (shallow pan, 1993-2008) covers it, with more options in the transmission filters collection.
• Shift solenoid B — same age, same heat, one bolt away. Do not leave it.
• The internal case connector and solenoid pigtail — inspect for fluid intrusion and green or chalky corrosion on the terminals. This is exactly the "damaged wires or connectors" failure the code lists.
• Solenoid O-rings and screen — cheap, and a torn O-ring turns an electrical repair into a pressure complaint.

Cost and effort

This is a pan-down job, not a teardown. A DIYer with a jack, stands, a drain pan, and a socket set can do it in an afternoon; expect roughly two to three hours of shop labor for pan, filter, and solenoid replacement, longer on 4WD trucks and vans where crossmembers and exhaust are in the way. Difficulty is moderate — the hard part is diagnosis, not wrenching.

The cost risk on P0973 is entirely in misdiagnosis. A pan-down solenoid job is a modest bill. A PCM replacement with programming is a large one, and a rebuild you did not need is larger still. Spending twenty minutes with an ammeter before you buy anything is the highest-return work on this code.

FAQ

Can I drive with P0973?

You should not plan to. RepairPal classifies the code as urgent and requiring prompt attention to prevent vehicle damage (RepairPal). Because losing solenoid A removes gear states from the binary shift logic, the transmission may hold a gear far past where it should shift, which loads the clutch packs and drives fluid temperature up.

Is P0973 always a bad shift solenoid?

No. The listed causes also include damaged wires or connectors, a defective control circuit, low or dirty fluid, and in rarer cases a failed TCM, PCM, or ECM (YourMechanic). Both Sonnax and Transmission Digest document real 4L60E cases where the computer's solenoid driver, not the solenoid, was the fault.

What resistance should a good 4L60E shift solenoid read?

GM's diagnosis charts specify 19-31 ohms for the shift solenoids on this unit, and a healthy circuit in a documented case measured 26.5 ohms on the 1-2 circuit and 27 ohms on the 2-3 circuit (Transmission Digest). Test under load with an ammeter rather than resistance alone, since a circuit can pass an ohm check and still fail when current flows.

Sources

• Transmission Digest — "Diagnosing an unusual problem: A slow-to-respond solenoid," Gordon Kehler (January 26, 2023)
• Transmission Digest / Sonnax TASC Force — "Load-Testing Solenoid Circuits," Gregg Nader
• Sonnax — "4L60-E Flares on 2-3 Shift? Could be a Bad Computer," Gregg Nader
• Transmission Rebuilders Network (TRNW) — 4L60E diagnostic trouble code index
• RepairPal — OBD-II Code P0973: Shift Solenoid "A" Control Circuit Low
• YourMechanic — P0973 OBD-II Trouble Code: Shift Solenoid A Control Circuit Low