ChassisC121F

Caution

Severity: Caution - get it checked when you can

If CAN signals are not entered from the door module at the passenger's seat that controls the side mirror (indicator) in the passenger's seat, BSD ECU sets DTC and turns off BSD switch LED and inhibits system operation

11 brands affected · Description from Hyundai data.

Key terms: ABS: anti-lock braking, which stops the wheels locking · Stability control: helps stop the car skidding · Wheel speed sensor: measures how fast each wheel turns

1What it means in plain English

A chassis system has a fault, usually ABS, traction control or stability control, but some makes use this range for airbags, electric power steering or park brakes.

2Common causes

Faulty wheel speed sensor
Damaged sensor ring or wiring
Faulty ABS module
Low brake fluid
Wheel bearing damage

3Can I drive?

Caution · drive with care

If the code names an airbag or SRS system, the airbag may not deploy in a crash: have it diagnosed promptly. If it names electric power steering, the assist may fail and the steering can become heavy: stop safely if that happens. If it names the brakes or park brake, have it checked before driving when braking feels abnormal. Otherwise ABS and stability control may be disabled: drive carefully, especially in wet conditions, and have it checked soon.

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 11

Brand	Code	Description	System
Chery	C121F	Power supply chip fault Brand	Chassis
Daewoo	C121F	No description available	Chassis
GM	C121F	No description available	Chassis
Holden	C121F	Electronic Brake Control Module Supervision Software Malfunction Brand	Chassis
Hyundai	C121F	If CAN signals are not entered from the door module at the passenger's seat that controls the side mirror (indicator) in the passenger's seat, BSD ECU sets DTC and turns off BSD switch LED and inhibits system operation Brand	Chassis
Opel	C121F	No description available	Chassis
Peugeot	C121F	No description available	Chassis
Saab	C121F	No description available	Chassis
MG (SAIC)	C121F	System Voltage Erratic OR System Voltage Low OR System Voltage High Brand	Chassis
Suzuki	C121F	No description available	Chassis
Toyota	C121F	No description available	Chassis

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 1

These 7-character codes are manufacturer-specific variants of C121F and may be reported by some scan tools.

Brand	Code	Description	System
Porsche	C121F13	fan supply - open load Brand	Chassis

6Related codes

Browse Cxxx codes or C121xx codes.