Faulty or worn mode switch (internal contacts dirty, worn or stuck); Damaged wiring to the switch, such as chafed, broken or shorted wires; Corroded, loose or contaminated connector at the switch or control unit; Moisture or spilled drink inside the switch or centre console; Fault in the transmission control unit or a related body control module that reads the switch; Outdated control unit software causing a false fault, where the manufacturer has issued a known update.

P071D

Transmission Mode Switch B Circuit.

Generic
Powertrain
Generic code
Low severity

How this code is built

P: SystemPowertrain
0: Defined bySAE, the same on every car
7: AreaTransmission
1D: FaultThe specific fault in that area

What it means

P071D is the generic code for a fault in the Transmission Mode Switch B circuit. The transmission control unit monitors the signal from the driver-operated mode switch (for example sport, economy, snow or tow/haul, depending on the vehicle) and has seen a voltage or signal that is out of range or does not make sense. The exact type of fault and switch position depend on the make, model and gearbox.

Symptoms

Gearbox warning light or engine management light on
Selected drive mode (sport, economy, snow, tow) does not engage or does not change shift behaviour
Gearbox stuck in a default shift programme
Mode indicator on the dash flickers, does not display or shows the wrong mode
Harsh, late or unexpected gear changes
Intermittent fault that comes and goes with switch movement

Possible causes

Faulty or worn mode switch (internal contacts dirty, worn or stuck)likely
Damaged wiring to the switch, such as chafed, broken or shorted wireslikely
Corroded, loose or contaminated connector at the switch or control unitlikely
Moisture or spilled drink inside the switch or centre consolepossible
Fault in the transmission control unit or a related body control module that reads the switchrare
Outdated control unit software causing a false fault, where the manufacturer has issued a known updaterare

How to diagnose

Read all stored and pending codes and note any related to other switches, the shift selector or network communication
Review freeze frame data to see when the fault set, and check whether it is current or historic
Operate the mode switch while watching live data for switch state, and see whether it responds in every position
Visually inspect the switch, console area and wiring for damage, water ingress or spilled liquid
Disconnect and inspect the switch and control unit connectors for corrosion, bent pins or poor terminal tension
Check the switch circuit supply, signal and earth with a multimeter against the manufacturer's wiring diagram and specification
Wiggle test the harness with live data open to find intermittent faults
Check for technical service bulletins and available software updates for the specific model and gearbox

How to fix

Replace the mode switch if it fails electrical tests or does not respond properly
Repair or replace damaged wiring and re-secure the harness
Clean or replace corroded or damaged connectors and terminals
Dry out and clean affected areas, replacing the switch if moisture has damaged it
Update the control unit software if an outdated calibration is a known cause for the vehicle
Repair or replace the control unit only after the switch, wiring and supply have been proven good

Can I keep driving?

Low severity

The car can usually be driven, as the gearbox normally defaults to a standard shift mode, though shifting may feel different. Book it in soon, and stop if the gearbox goes into limp mode or shifts harshly.

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