Faulty heated catalyst power switch (solid-state relay) that is failing and overheating internally; Shorted or partially shorted heating element in the bank 2 catalytic converter, causing excessive current draw; Damaged or corroded wiring and connectors between the power switch and the heated catalyst; Poor ground connection for the heated catalyst circuit, leading to increased resistance and heat; Engine control module software or internal driver fault incorrectly interpreting switch temperature; Aftermarket or incorrect heated catalyst components that do not match BMW specifications

DTC codes / BMW codes / P1405

P1405 · BMWHeated Catalyst Power Switch Overtemperature Condition Bank 2

P1405 on BMW vehicles indicates that the engine control module has detected an overtemperature condition in the power switch circuit for the bank 2 heated catalytic converter. The heated catalyst system uses an electrical heating element to bring the catalyst up to operating temperature quickly after a cold start, reducing emissions, and the power switch is the solid-state relay that controls current flow to that heater. The module monitors the switch temperature and sets this code when the switch exceeds its safe thermal limit, which can be caused by a failing switch, excessive current draw from the heater element, or a wiring fault.

SystemPowertrain

Code typeBMW specific

SeverityMedium

Fix difficultyIntermediate

AreaAuxiliary emission controls

Symptoms you may notice

Illumination of the check engine light, often with no other noticeable symptoms
A burning or hot electrical smell from the underhood or underbody area near the catalytic converter
Rough running or hesitation during the first few minutes after a cold start
Reduced fuel economy or slightly elevated emissions during warm-up
In rare cases, a no-start condition if the power switch fails shorted and drains the battery

Common causes, most likely first

Faulty heated catalyst power switch (solid-state relay) that is failing and overheating internally
Shorted or partially shorted heating element in the bank 2 catalytic converter, causing excessive current draw
Damaged or corroded wiring and connectors between the power switch and the heated catalyst
Poor ground connection for the heated catalyst circuit, leading to increased resistance and heat
Engine control module software or internal driver fault incorrectly interpreting switch temperature
Aftermarket or incorrect heated catalyst components that do not match BMW specifications

How to diagnose and fix it

Scan all modules for stored codes and freeze-frame data, and verify battery voltage and charging system health before proceeding
Visually inspect the heated catalyst power switch, its connectors, and the wiring harness for signs of overheating, melting, or corrosion
Measure resistance of the bank 2 heated catalyst heating element and compare to BMW specifications to rule out a shorted heater
Check the power switch control signal and ground circuit with a multimeter or oscilloscope while commanding the heater on with a scan tool
Test the power switch by measuring voltage drop across it under load; excessive drop indicates a failing switch
If the switch is faulty, replace it and clear the code, then verify the heater operates and the code does not return
If the heating element is shorted, replace the bank 2 catalytic converter assembly and recheck the circuit

Before you replace the heated catalyst

A corroded ground strap on the engine or chassis can cause the power switch to overheat because the circuit seeks ground through unintended paths, so always check grounds before condemning the switch.
The power switch is often misdiagnosed as the catalytic converter itself; a shorted heater element will quickly destroy a new switch, so test the element resistance first.
BMW heated catalyst systems are sensitive to aftermarket replacement components, and a non-OEM switch or converter can set this code even when the circuit appears functional.
Intermittent P1405 codes that appear only in cold weather often point to a weak battery or poor connection that causes the switch to work harder during heat-up.
The engine control module may set P1405 as a protective measure when it detects a switch temperature above threshold, but the actual root cause can be a wiring harness chafe hidden behind the engine block.

Can I keep driving with P1405?

You can usually drive the vehicle short distances to a repair shop, but avoid prolonged driving or heavy loads because an overheating power switch can lead to a fire risk or complete failure of the heated catalyst system. If you smell burning or see smoke, stop driving immediately and have the vehicle towed.

Tools that help

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Guidance is general and written for BMW vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.