Faulty shift solenoid B (internal open circuit, short or sticking); Damaged, chafed or corroded wiring between the solenoid and the transmission control unit; Poor connection at the transmission internal harness connector or plug (corrosion, bent pins, fluid ingress); Low, contaminated or degraded transmission fluid affecting solenoid operation; Blocked valve body passages or worn valve body contaminating the solenoid; Low battery voltage or poor earth causing unreliable solenoid control; Faulty transmission control unit driver circuit.

P0755

Shift Solenoid B.

Generic
Powertrain
Generic code
Medium severity

How this code is built

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

What it means

P0755 is the generic code for a fault in the shift solenoid 'B' circuit in an automatic transmission. The transmission control unit commands the solenoid on or off and monitors the circuit. It sets the code when the electrical feedback does not match the command, such as an open circuit, a short or a resistance outside the expected range. Which gear changes solenoid B controls depends on the transmission, so the exact effect varies by model.

Symptoms

Gearbox warning light or malfunction indicator lamp on
Gearbox stuck in one gear (limp mode), often second or third
Harsh, delayed or flared gear changes
Missing gears or no upshift or downshift
Poor acceleration or higher fuel consumption
Possible no reverse or no engagement, depending on the gearbox

Possible causes

Faulty shift solenoid B (internal open circuit, short or sticking)likely
Damaged, chafed or corroded wiring between the solenoid and the transmission control unitlikely
Poor connection at the transmission internal harness connector or plug (corrosion, bent pins, fluid ingress)likely
Low, contaminated or degraded transmission fluid affecting solenoid operationpossible
Blocked valve body passages or worn valve body contaminating the solenoidpossible
Low battery voltage or poor earth causing unreliable solenoid controlpossible
Faulty transmission control unit driver circuitrare

How to diagnose

Read all stored and pending codes and record the freeze frame data, noting road speed, gear selected and fluid temperature if available
Check the transmission fluid level and condition (colour, smell, debris), following the procedure for that model as some units are sealed or need a set temperature
Check battery condition and charging voltage, and inspect the main earths, as low voltage can set solenoid faults
Inspect the external wiring and connector to the gearbox for damage, corrosion, fluid ingress and bent or pushed-back pins
Using the manufacturer's data, measure the solenoid B resistance at the connector and compare it with specification
Check the wiring for continuity, short to earth and short to supply between the solenoid and the control unit
Use live data or an actuator test, where supported, to see whether solenoid B responds when commanded
If the electrical checks pass, inspect the internal harness, solenoid and valve body as the procedure for that transmission requires

How to fix

Replace the faulty shift solenoid B, or the solenoid pack if it is only supplied as an assembly
Repair or replace damaged wiring and clean or replace corroded or damaged connectors
Replace the internal transmission harness or connector if the fault is found there
Correct the fluid level or replace the fluid and filter using the specified type and procedure
Clean or overhaul the valve body if it is contaminated or worn
Repair the battery, charging or earth fault, then clear the code and road test to confirm it does not return

Can I keep driving?

Medium severity

The car can usually be driven gently to a garage, as the gearbox normally goes into limp mode. Avoid heavy loads and hard driving, and get it fixed soon, because continued driving with wrong gear changes can cause further transmission damage.

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