OBD-II trouble code
P0973: Shift Solenoid "A" Control Circuit Low
A shift solenoid held on when it should be off does not spoil one gear — it removes every gear whose combination needed that valve closed. Which is why the list of gears the car still has is a map back to the fault, and why you can often name the circuit before opening the toolbox.
Quick facts
- System
- Powertrain
- Category
- Transmission / Shift Control
- Severity
- High severity
- Drivable
- Usually safe to drive short-term
- Repair cost range
- $130 – $1,200
- DIY difficulty
- Advanced DIY
One of 43 shift solenoid codes
P0973 sits in a grid: one axis is which solenoid the letter refers to, the other is what went wrong with it. Each cell is a genuinely different fault with its own diagnosis — but codes from the same row or column often appear together, and what a pairing means is usually the fastest way in. The hub page lays out all 43 and explains how to read them against each other.
See all shift solenoid codes →Browse every code in P0900–P0999, or start from the full code library.
What does P0973 mean?
P0973 says the module measured its shift solenoid 'A' output sitting low when it had commanded it off. On a ground-switched output that means something else is providing a path to ground — a chafed wire against the case, a shorted coil, fluid bridging pins in a connector — and the coil is energised whether the module wants it or not.
Understanding what that does to the car requires one idea: a transmission's gear selection is a truth table. Each gear is produced by a specific pattern of solenoid states, and the same solenoid appears in several rows of that table, on in some and off in others. So a solenoid stuck permanently on does not delete one gear. It deletes every row of the table that required it to be off, and leaves intact every row that wanted it on. That is why a single circuit fault takes out an apparently arbitrary set of ratios while others work perfectly, and why the pattern looks so strange to a driver — first and fourth fine, second and third missing, or the car pulling away in a higher gear than it should.
That pattern is the most valuable diagnostic in this whole subject, and it costs nothing. Write down which gears the transmission will and will not select, then compare that list against the manufacturer's solenoid application table for the transmission. Almost always, exactly one solenoid state explains the whole pattern. You can arrive at a workshop already knowing which circuit is at fault, and more usefully, you can tell whether the pattern is consistent with a solenoid stuck on at all — if the surviving gears do not fit any single solenoid state, the problem is not one stuck solenoid and someone is about to replace the wrong part.
There is a second observation the truth table explains. Because the module knows which gear it commanded and can compute which gear it actually got from input and output shaft speed, a stuck-on solenoid usually stores a gear ratio code alongside this one, naming the specific ratio that went wrong. That is the same shortcut the range and performance code offers, and it is worth reading before any wiring is disturbed.
When the module detects a shorted output it normally protects itself by switching that driver off. That has a consequence people misread constantly: the fault behaves like an intermittent. Everything is fine for a few seconds after a start, the module notices the short, the driver latches off, the transmission drops into its failsafe strategy, and the car stays that way until the ignition is cycled — at which point it is briefly fine again. That is a completely consistent electrical fault being reset by the key, not a wandering one, and treating it as intermittent sends people looking for a fault that only appears on rough roads.
On the repair side, the distribution of causes here differs from the pressure control circuits, for a physical reason. Some transmissions carry their shift solenoids in an externally mounted pack bolted to the case, with wiring that lives in the open air alongside the exhaust, the driveshafts and the subframe. Where that is the design, external chafe and connector corrosion are far more likely than an internal coil failure, and the repair does not require opening the transmission at all. It is worth establishing which layout the vehicle uses before quoting the job, because the two versions of this repair are separated by several hundred dollars and half a day.
Common causes
- Control wire chafed to ground against the case, a bracket, the subframe or an exhaust component
- Shift solenoid 'A' with shorted windings
- Fluid or water bridging pins to the earthed shell of the transmission case connector
- Corroded terminal contacting the connector body
- Internal transmission harness rubbed through against a rotating part
- Harness pinched during clutch, subframe, exhaust or transmission work
- Failed output driver in the transmission control module stuck low
- Rodent damage to an externally routed solenoid harness
- Incorrect replacement solenoid with a coil resistance below specification
Symptoms
- Specific gears missing while others work perfectly normally
- Vehicle pulling away in a higher gear than it should
- Transmission dropping into a fixed failsafe gear shortly after every start
- Normal operation for a few seconds after each ignition cycle, then failure again
- A gear ratio code from the P0730 family stored alongside this one
- Harsh or abrupt engagement into the gears that do still work
- Reduced top speed and high engine speed if the failsafe ratio is a low one
- Check engine light with the transmission warning lamp on vehicles that have one
Diagnostic steps
- 1.Write down exactly which gears the transmission will and will not select, then compare that list against the manufacturer's solenoid application table — one solenoid state usually explains the entire pattern.
- 2.If no single solenoid state explains the surviving gears, stop and reconsider, because the fault is not one stuck solenoid and a replacement will not fix it.
- 3.Read every stored code first; a gear ratio code from the P0730 family names the specific ratio that failed.
- 4.Establish whether this transmission carries its shift solenoids internally or in an externally mounted pack, since that decides whether this is a pan-off job or an open-air one.
- 5.With the ignition off and the case connector unplugged, measure resistance from the solenoid control pin to a clean chassis ground; near zero on a pin that should be isolated proves the short is outside the module.
- 6.Measure coil resistance across the solenoid pins to separate a shorted winding from a shorted wire.
- 7.Inspect externally routed harness sections where they cross brackets, the case and the exhaust, looking for the polished witness mark that precedes a short.
- 8.Do not treat the after-start-then-limp behaviour as intermittent; it is the module latching its own output off and the key cycle resetting it.
- 9.Repair the wiring before fitting a new solenoid, because a fresh part cannot be validated while the short is still pulling the circuit down.
Repair cost
$130 – $1,200
Diagnosis is $110 to $220, and on this code a shop that reads the surviving-gears pattern properly should reach a verdict quickly. An external wire or connector repair is $130 to $400 and is the most likely outcome on transmissions with an externally mounted solenoid pack. Shift solenoid replacement is $250 to $700 fitted where the pan has to come down, and toward the low end where the pack is external. A damaged internal harness is $500 to $1,100. A failed module output driver is the expensive branch at $600 to $1,200 with programming. Fluid and filter are usually included once the pan is off.
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DIY vs shop
This is an advanced DIY job. It typically requires specialty tools, scan-tool access, lifting equipment, or careful sequencing to avoid causing new failures. Plan for extended downtime and have a backup vehicle. Most owners are better served by a shop that has done this repair before.