BodyB1D91

Caution

Severity: Caution - get it checked when you can

Heater field effect transistor failure

2 brands affected · Description from Land Rover data.

Key terms: Control module: a small computer that runs one part of the car

1What it means in plain English

A body system has a fault. Depending on the make, this range can include airbags and seat belts, windows, locks and climate control, and also charging, brake, oil or coolant sensors.

2Common causes

Wiring or connector fault
Faulty sensor or switch
Water or corrosion in a connector
Control module fault
Low battery voltage

3Can I drive?

Caution · drive with care

Do not assume this code is safe to drive. If it concerns the brakes, brake vacuum, charging/alternator, engine oil or coolant, have it diagnosed before driving. Airbags or seat belts may not work in a crash, and a brake or charging fault can leave the car unsafe or stranded. For convenience systems (windows, locks, climate), have it checked when convenient.

This page gives general information. It is not professional advice. For a definite diagnosis and a repair quote, ask a qualified mechanic to inspect the car.

4Brand data 2

Brand	Code	Description	System
DFFS	B1D91	Left front sensor signal line is open or shorted to ground Brand	Body
Land Rover	B1D91	Heater field effect transistor failure Brand	Body

Legend: SAE is the generic J2012 description; Brand is text taken from that manufacturer’s data. Manufacturer rows keep the wording and language of the source data, and non-English text is tagged so screen readers pronounce it correctly.

5Extended variant codes 11

These 7-character codes are manufacturer-specific variants of B1D91 and may be reported by some scan tools.

Brand	Code	Description	System
Mercedes-Benz	B1D9103	Das Steuergerät 'Fahrerassistenzsystem' hat Funktionsstörung. There is a frequency or pulse width modulation fault. Brand	Body
Mercedes-Benz	B1D9104	Control unit 'Driver assistance system' has a malfunction. System Internal Failure Brand	Body
Mercedes-Benz	B1D9105	Control unit 'Driver assistance system' has a malfunction. System Programming Failure Brand	Body
Mercedes-Benz	B1D9106	Control unit 'Driver assistance system' has a malfunction. Algorithm Based Failure Brand	Body
Mercedes-Benz	B1D911F	Das Steuergerät 'Fahrerassistenzsystem' hat Funktionsstörung. Circuit Intermittent Brand	Body
Mercedes-Benz	B1D9147	Control unit 'Driver assistance system' has a malfunction. There is a runtime error. Brand	Body
Mercedes-Benz	B1D9153	Control unit 'Driver assistance system' has a malfunction. The component is deactivated. Brand	Body
Mercedes-Benz	B1D9156	Control unit 'Driver assistance system' has a malfunction. An incorrect or incompatible configuration was detected. Brand	Body
Mercedes-Benz	B1D917E	Control unit 'Driver assistance system' has a malfunction. The actuator does not switch off. Brand	Body
Mercedes-Benz	B1D9196	Control unit 'Driver assistance system' has a malfunction. Component Internal Failure Brand	Body
Mercedes-Benz	B1D91E0	Control unit 'Driver assistance system' has a malfunction. Brand	Body

6Related codes

Browse Bxxx codes or B1D9xx codes.