Short to earth or chafed wiring in the pressure sensor or switch circuit; Faulty transmission fluid pressure sensor or switch D; Corroded, damaged or contaminated connector at the sensor, valve body or control module; Low or degraded transmission fluid, or the wrong fluid, causing genuinely low pressure; Internal hydraulic fault such as worn clutch seals, a weak pump or valve body wear; Fault in the transmission control module or its supply or earth; Outdated control module software on certain models.

P0877

Transmission Fluid Pressure Sensor/Switch D Circuit Low.

Generic
Powertrain
Generic code
Medium severity

How this code is built

P: SystemPowertrain
0: Defined bySAE, the same on every car
8: AreaTransmission
77: FaultThe specific fault in that area

What it means

P0877 is a generic powertrain code meaning the transmission control module has detected a low voltage or low signal in the circuit of transmission fluid pressure sensor/switch 'D'. The module saw a signal below the expected range, which can come from a wiring fault, a failed sensor or switch, or a genuine hydraulic pressure problem. Which sensor or switch is 'D', and where it sits in the gearbox, depends on the vehicle and transmission.

Symptoms

Gearbox warning light or malfunction indicator lamp on
Gearbox stuck in limp mode or a fixed gear
Harsh, delayed or flaring gear changes
Slipping or loss of drive in certain gears
Poor fuel economy or reduced performance
Gearbox may not select certain gears or ratios

Possible causes

Short to earth or chafed wiring in the pressure sensor or switch circuitlikely
Faulty transmission fluid pressure sensor or switch Dlikely
Corroded, damaged or contaminated connector at the sensor, valve body or control modulelikely
Low or degraded transmission fluid, or the wrong fluid, causing genuinely low pressurepossible
Internal hydraulic fault such as worn clutch seals, a weak pump or valve body wearpossible
Fault in the transmission control module or its supply or earthrare
Outdated control module software on certain modelsrare

How to diagnose

Read all stored and pending codes and the freeze frame data, noting gear, fluid temperature and speed when the code set
Check the transmission fluid level and condition, following the manufacturer's procedure for that gearbox, as many are sealed or need a set temperature
Visually inspect the wiring and connectors to the pressure sensor or switch for chafing, fluid ingress, corrosion and bent pins
Using the manufacturer's data, view the live fluid pressure sensor or switch reading and compare it with the expected value in each state
Measure the sensor supply voltage, reference and earth, and check the signal wire for a short to earth with the harness disconnected
Check for related codes or other gearbox faults that may point to a hydraulic problem rather than an electrical one
Check for applicable service bulletins or software updates for the model and transmission
If the electrical side is sound, carry out a line pressure test or further internal diagnosis as specified for that gearbox

How to fix

Repair or replace damaged wiring and fix any short to earth in the circuit
Clean or replace corroded or damaged connectors and terminals
Replace the faulty fluid pressure sensor or switch, with the correct fluid and sealing as the manufacturer specifies
Correct the fluid level or replace the fluid with the specified type if it is low, degraded or wrong
Repair the internal hydraulic fault, such as the pump, seals or valve body, if pressure testing confirms it
Update the control module software if an updated calibration is known to address the fault, or repair the module if it is proven faulty

Can I keep driving?

Medium severity

The car may drive in limp mode, but continued use with low hydraulic pressure or slipping can cause expensive gearbox damage. Get it checked soon and avoid heavy loads or long journeys until it is fixed.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.