OBD-II trouble code
P0971: Pressure Control Solenoid "C" Control Circuit High
The mildest-feeling code in the whole pressure control block and the easiest to leave alone — nothing shifts wrong, nothing bangs. What it costs you turns up on the fuel gauge and in the transmission's temperature, which is precisely why it gets ignored for years.
Quick facts
- System
- Powertrain
- Category
- Transmission / Pressure Control
- Severity
- High severity
- Drivable
- Usually safe to drive short-term
- Repair cost range
- $0 – $1,600
- DIY difficulty
- Shop recommended
One of 27 pressure control solenoid codes
P0971 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 27 and explains how to read them against each other.
See all pressure control solenoid codes →Browse every code in P0900–P0999, or start from the full code library.
What does P0971 mean?
P0971 means the module measured voltage on the third pressure control solenoid's control circuit that stayed high when it should have been pulled down. Electrically that is either an open — a broken wire, a disconnected plug, a failed coil — or a connection to a source of voltage that has no business being there. Statistically, on this circuit, it is usually an open, and an open is the reason this page reads differently from every other code in the block.
Where the 'C' circuit meters torque converter clutch apply, an open means the clutch simply never applies. There is no bang, no flare, no slip through a gear change, no limp mode on most vehicles. Every shift happens exactly as it always did. What you lose is the direct mechanical coupling between engine and transmission at cruise, so the converter goes back to doing the whole job hydraulically, and hydraulic coupling is never one hundred percent efficient.
That has two measurable consequences and no dramatic ones. The first is engine speed. With lockup working, a car at a steady seventy might sit at two thousand rpm; without it, the same road speed typically needs a couple of hundred to four hundred rpm more, and the difference is visible on the tachometer if you know what the number used to be. The second is fuel. A fuel penalty in the region of five to ten percent on motorway journeys is a realistic expectation, which is why a surprising number of these codes are found not by a warning light but by an owner who noticed their long-run economy fell off and could not explain it.
The reason this page rates the code seriously despite a car that drives perfectly is heat. Converter slip losses go somewhere, and where they go is into the transmission fluid. Lockup exists partly to stop that happening for hours at a time on a motorway. Remove it and the fluid runs hotter than the design intends on exactly the journeys where it is under load longest — long distances, hills and towing. Fluid temperature is the single biggest determinant of how long friction material, seals and the other solenoids last, so the bill for ignoring this one is not paid by the converter; it is paid later by everything else in the gearbox. On a vehicle used for towing, this is not a code to sit on.
Diagnosis has a natural first fork and it is cheap. With the transmission case connector unplugged, measure the resistance of the solenoid coil across its pins. A reading in the range the manufacturer specifies — commonly a few ohms for a pulse-width-modulated pressure control solenoid — means the coil and the internal harness are intact and the open is somewhere between that connector and the module, which is to say outside the transmission and reachable. An infinite reading means the break is inside the case, which is a very different job and a very different invoice. That one measurement, taken before anything is dismantled, decides which of those two conversations you are about to have.
Common causes
- Open circuit in the wiring between the module and the transmission case connector
- Failed solenoid 'C' with an open winding
- Broken or corroded terminal inside the transmission case connector
- Case connector not fully seated after a fluid service, filter change or cooler line repair
- Internal transmission harness broken where it flexes or passes a rotating component
- Control wire shorted to a battery-voltage circuit sharing the same loom
- Failed output driver in the transmission control module
- Corrosion in a bulkhead connector between the module and the transmission
- Solenoid connector unlatched during valve body work and never fully clipped home
Symptoms
- Engine speed several hundred rpm higher than usual at a steady motorway cruise
- Noticeably worse fuel economy on long runs with normal economy around town
- Torque converter clutch never engaging on a scan tool regardless of conditions
- Transmission fluid temperature running higher than normal, especially towing
- Gear changes that feel completely normal throughout
- Check engine light with no drivability complaint at all
- Transmission overheat warning on long climbs or with a trailer
- No change in behaviour after clearing the code
Diagnostic steps
- 1.Confirm from documentation what the 'C' circuit does on this transmission, because the entire symptom picture depends on whether it is converter apply or a clutch circuit.
- 2.With the ignition off and the transmission case connector unplugged, measure the solenoid coil resistance across its pins and compare it against the manufacturer's figure.
- 3.Use that reading to decide the job: a coil within specification puts the open outside the transmission, an open coil puts it inside the case.
- 4.Check continuity of the control wire from the module connector to the case connector before condemning anything, since a single broken strand produces this code.
- 5.Inspect the case connector for a partially seated body or an unlatched clip, particularly if the transmission has been serviced recently.
- 6.Watch commanded torque converter clutch state against engine and input shaft speed on a scan tool at a steady cruise to confirm the clutch never applies.
- 7.Record fluid temperature on a sustained motorway run, since heat rather than drivability is what this fault actually costs.
- 8.If the wiring and coil both check out, measure the module-side pin with the output commanded on to confirm whether the driver is pulling it down.
- 9.Check for stored codes on other circuits sharing the same feed if the fault turns out to be a short to voltage rather than an open.
Repair cost
$0 – $1,600
The low end is genuinely zero because an unlatched case connector reseated during diagnosis is a real and not uncommon outcome. Diagnosis is $120 to $250. An external wiring or terminal repair is $150 to $450. Solenoid replacement, which means dropping the pan and usually the valve body, is $650 to $1,500 fitted including fluid and filter. A broken internal harness is $500 to $1,100. A failed module output is $600 to $1,600 with programming. Against those numbers, weigh what the fault costs while it is left: five to ten percent of your motorway fuel indefinitely, plus fluid running hotter than designed, which is what shortens everything else in the gearbox.
Estimate your repair
Run the numbers for your vehicle
Open the Repair Cost Estimator with wiring harness / circuit repair preselected. Adjust labor rate and vehicle category to fit your situation.
DIY vs shop
Leave this one to a qualified shop. It typically involves emissions-critical components, refrigerant handling, or other work that requires manufacturer-grade tooling, training, or certification. DIY attempts often produce a more expensive problem than the original code.