P0871: Transmission Fluid Pressure Sensor/Switch C Circuit Range/Performance (Meaning, Causes, Fixes)
What P0871 means
The transmission fluid pressure sensor/switch (TFPS) turns hydraulic pressure inside the automatic transmission into an electrical signal for the powertrain control module (PCM) or transmission control module (TCM). OBD-Codes.com says it is usually mounted on the side of the valve body inside the transmission, though on some vehicles it screws into the transmission case, and that the PCM/TCM may share the reading with other modules over the vehicle's data network. The computer uses the signal to judge transmission operating pressure and when a shift is happening. OBD-Codes.com says this code sets when the "C" input doesn't match the normal operating voltages stored in the computer, and that it can also come from mechanical problems inside the transmission such as internal leaks, cracked or missing check balls in the valve body, low main line pressure or a stuck valve, which matters most when the fault is intermittent. RepairPal says the TCM detects an incorrect signal from the pressure sensor and has the PCM set the code. Which sensor is "C" depends on the vehicle, so check a repair manual for your model. OBD-Codes.com calls it a generic code that applies to OBD-II vehicles including Jeep, Dodge, Mazda, Nissan, Honda and GM. Note on sources: RepairPal titles P0871 "Transmission Fluid Pressure Sensor/Switch C Circuit" without the words range/performance (the same title it gives P0870). OBD-Codes.com's article at its P0871 address describes the "C" circuit range/performance fault but its headings label it P0846, which on the same site is the "B" circuit range/performance code, so that numbering looks like an error on their page. The two sources also differ on severity (RepairPal says Urgent; OBD-Codes.com says it depends and the computer can partly compensate). Related codes P0870 and P0872 through P0874 cover the same sensor's other circuit faults.
Severity: can I keep driving?
Stop and fix promptly
Get it checked promptly. RepairPal rates P0871 Urgent, meaning it can lead to serious damage and should be looked at right away. OBD-Codes.com is less absolute: it says severity depends on which circuit failed and that the engine or transmission computer can compensate to some degree, but the transmission may shift differently or go into limp mode (starting off in 2nd or 3rd gear). If the transmission slips, won't engage a gear, or shifts harshly, avoid driving it until it is diagnosed.
Common symptoms
- Check engine light on (OBD-Codes.com)
- Change in shift quality, or the transmission not shifting properly (OBD-Codes.com, RepairPal)
- Vehicle starts off in 2nd or 3rd gear (limp mode) (OBD-Codes.com)
- Increased fuel consumption (RepairPal)
Likely causes
Roughly most to least common, based on the sources below. Your vehicle may differ.
- Failed transmission fluid pressure sensor/switch; OBD-Codes.com rates this the likely cause (OBD-Codes.com, RepairPal)
- Open circuit, short to voltage or short to ground in the sensor signal wiring, or other wiring issues (OBD-Codes.com, RepairPal)
- Corroded or damaged connector terminals, especially outside the transmission case (OBD-Codes.com)
- Internal mechanical transmission problems such as internal leaks, damaged check balls, low main line pressure or a stuck valve (OBD-Codes.com)
- Failed TCM or PCM; OBD-Codes.com rates the PCM unlikely and notes a replacement must be programmed (OBD-Codes.com, RepairPal)
Diagnostic steps you can do
Work on a cool engine, parked on level ground with the parking brake set. Never work under a car supported only by a jack.
- Check for technical service bulletins (TSBs) for your vehicle; the problem may be a known issue with a known fix (OBD-Codes.com).
- If power-related codes or more than one pressure sensor/switch code are stored, diagnose those first, since they may be causing P0871 (OBD-Codes.com).
- Find the pressure sensor/switch connector and inspect the wiring for rubbing, bare wires, burn spots or melted plastic, and the terminals for burning or green corrosion. Clean corroded terminals with electrical contact cleaner and a plastic bristle brush, let them dry and apply electrical grease (OBD-Codes.com).
- Clear the code and drive to see if it returns; OBD-Codes.com says if it doesn't, the connection was most likely the problem, and that the external transmission connections are the most common trouble spot.
Typical fixes
- Clean or repair corroded connectors and damaged wiring in the sensor circuit
- Replace the transmission fluid pressure sensor/switch if testing shows it is out of spec
- Repair internal transmission problems (valve body, check balls, line pressure) if the sensor and wiring check out
- Replace and program the TCM or PCM only after the sensor, wiring and transmission have been ruled out
Repair costs vary widely by vehicle, region, parts brand and shop, so we don't quote prices. Get a written estimate after diagnosis.
🛠 When to call a pro
- With the sensor unplugged and key on, engine off, the harness signal terminal should show the manufacturer's reference voltage (OBD-Codes.com says either 12 or 5 volts depending on the vehicle); a wrong reading points to wiring or the computer (OBD-Codes.com)
- Checking the sensor's resistance against factory specs with an ohmmeter while wiggling the connector needs the service information for your vehicle (OBD-Codes.com)
- The sensor is often on the valve body inside the transmission, so reaching it may mean removing the transmission pan (OBD-Codes.com describes the location)
- The code keeps coming back after a new sensor, which OBD-Codes.com says can mean an internal transmission fault or, less likely, a failed PCM/TCM that must be programmed to the vehicle
Where to buy
Plain search links. Always match parts to your exact year, make, model and engine.
FAQs
Is P0871 serious?
RepairPal rates it Urgent. OBD-Codes.com says severity depends on the circuit and the computer can partly compensate, but shifting may change or the transmission may go into limp mode. Have it checked promptly, and don't keep driving if the transmission slips or won't shift.
What is the difference between P0870 and P0871?
Both concern transmission fluid pressure sensor/switch "C". P0870 is a general circuit fault, while P0871 means the signal is out of the expected range. RepairPal gives both the same title, so read the code number your scanner shows.
Is P0871 always a bad pressure sensor?
No. OBD-Codes.com rates a failed sensor the likely cause, but wiring, corroded connectors and internal transmission problems can also set it, and RepairPal lists a failed TCM.
How much does it cost to fix P0871?
Neither source gives a repair cost. The fix can range from cleaning a connector to replacing the sensor or repairing the transmission, so get a diagnosis and a written estimate first.
Sources
Last reviewed 2026-10-23. Code definitions and repair steps can vary by manufacturer. Confirm with your vehicle's service information.