A transmission pressure switch is reading out of range, so the module cannot confirm the pressures it is commanding.
P0871 — also written PO871, P 0871, 0871 — is the OBD-II code for transmission fluid pressure sensor/switch 'c' range/performance. Same code, same fix: this page covers every spelling of it.
P0871 is a transmission fault code, typically costing £180–£1500 to put right in a UK garage.
What causes P0871?
- Low fluid level
- Blocked filter restricting flow
- Failed pressure switch
- Internal leak in the valve body
How P0871 is fixed
- Check fluid level at the correct operating temperature
- Fluid and filter service
- Replace the pressure switch or valve body
P0871 repair cost in the UK
Most P0871 repairs land between £180–£1500 including parts and labour. The spread is wide because the cheap fix (a sensor, a hose, a leak) and the expensive fix (a major component) throw the same code — which is why a proper diagnosis before parts are bought saves the most money.
Can you drive with P0871?
Drive gently; avoid towing and motorway speeds.
Urgency: high.
What P0871 is telling you
Transmission codes come from the gearbox control unit comparing commanded gear, clutch or solenoid state against the speeds its sensors report. A mismatch triggers a protection strategy, which is what the driver feels as limp mode or a locked gear.
On P0871 specifically — transmission fluid pressure sensor/switch 'c' range/performance — the stored code records the moment that check failed, not the moment the part gave up. That gap is why two cars with the same code can need completely different repairs.
How P0871 is diagnosed properly
Each of the known causes is ruled in or out in cost order, cheapest and most likely first. On P0871 that means working through them like this:
- Low fluid level — checked for level and condition first, as the cheapest possible cause and a common one.
- Blocked filter restricting flow — measured as a pressure or flow difference across the component, so a partial restriction is not mistaken for a clear one.
- Failed pressure switch — confirmed with live data before any part is bought.
- Internal leak in the valve body — commanded on and off with the diagnostic tool while its current draw and movement are watched, which separates a stuck part from a dead circuit.
An hour of diagnostic time on P0871 routinely saves more than it costs, because the alternative is buying the most expensive part on that list and hoping.
The repairs that actually clear P0871
- Check fluid level at the correct operating temperature
- Fluid and filter service
- Replace the pressure switch or valve body
After the repair the code is cleared and the car is driven until the relevant readiness monitor completes, rather than handed back as soon as the light goes out. A code that has only been erased will come straight back on the next drive cycle.
What happens if P0871 is ignored
Leaving this one is the expensive choice. The protection strategy the ECU falls into is there to limit damage, and every mile driven with the fault active is a mile the engine or gearbox spends outside its designed operating window.
For reference, P0871 typically lands at £180–£1500 all-in at an independent garage in the UK — main-dealer quotes for the same job usually sit above that.
Getting P0871 looked at
Bob's Mechanical Repairs is an independent garage in Birnam, Dunkeld, Perthshire, with 32 years of Bob's experience on the tools. If P0871 is showing on your car, bring the scan results with you — we will read the live data ourselves, tell you which of the causes above it actually is, and price the repair before any work starts.