NetworkU0121

Serious

Severity: Serious - have it checked soon

Lost Communication With Anti-Lock Brake System (ABS) Control Module

43 brands affected · Generic SAE J2012 description.

Key terms: ABS: anti-lock braking, which stops the wheels locking · Control module: a small computer that runs one part of the car · SAE J2012: the standard generic code list

Safety: This code relates to the braking system or brake assist. Braking may be affected.

1What it means in plain English

One or more control modules have lost communication with the ABS control module.

2Common causes

Wiring or connector fault on the communication bus
Faulty ABS control module
Low battery voltage or poor ground
Water ingress in a connector or module

3Can I drive?

Serious · drive with care

Have it checked immediately: brakes or brake assistance may be affected. Do not drive if the pedal feels soft or hard, the car pulls when braking, or the brake warning light is on.

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 43

Brand	Code	Description	System
Ashok Leyland CV	U0121	Lost Communication With Anti-Lock Brake System (ABS) Control Module SAE	Network
BAIC Motor	U0121	CAN ABS Communication Brand	Network
Mercedes-Benz	U0121	Lost Communication With Anti-Lock Brake System (ABS) Control Module SAE	Network
BYD	U0121	Communication with ABS fault Brand	Network
Chery	U0121	ESP signal lost Brand	Network
Chrysler	U0121	Lost Communication With Anti-Lock Brake Module Brand	Network
Daewoo	U0121	CAN-Bus no Communication with ABS/TC Brand	Network
Daihatsu	U0121	ABS/VSC fault Brand	Network
DFFS	U0121	No speed signal Brand	Network
DFFX	U0121	ECM lost communication with ABS Brand	Network
DFXK	U0121	ECM Lost Communication with ABS Brand	Network
EOBD	U0121	Yhteys estynyt ABS-ohjausmoduuliin 'A' Brand	Network
Fiat	U0121	Lost communication with anti-Lock brake module Brand	Network
Ford	U0121	Lost Communication With Anti-Lock Brake System (ABS) Control Module SAE	Network
Geely	U0121	Speed sensor fault Brand	Network
GM	U0121	Lost Communication With Anti-Lock Brake System (ABS) Control Module Brand	Network
Great Wall	U0121	CAN ABS Communication Brand	Network
Hafei	U0121	Lost Communication With Anti-Lock Brake System (ABS) Control Module Brand	Network
Holden	U0121	Lost Communication with Electronic Brake Control Module Brand	Network
Honda	U0121	Lost Communication With Anti-Lock Brake System (ABS) Control Module SAE	Network
Hyundai	U0121	Lost Communication With Anti-Lock Brake System (ABS) Control Module SAE	Network
Isuzu	U0121	Lost Communication With Anti-Lock Brake System (ABS) Control Module SAE	Network
Land Rover	U0121	Lost Communication With Anti-Lock Brake System (ABS) Control Module SAE	Network
Mahindra	U0121	Lost Communication With Anti-Lock Brake System (ABS) Control Module SAE	Network
Maserati	U0121	Lost Communication With Anti-Lock Brake System (ABS) Control Module Missing Message Brand	Network
Mazda	U0121	Lost Communication With Anti-Lock Brake System (ABS) Control Module SAE	Network
Mitsubishi	U0121	ABS/ASC CAN timeout Brand	Network
Nissan	U0121	Lost Communication With Anti-Lock Brake System (ABS) Control Module SAE	Network
Opel	U0121	Lost Communication With Anti-Lock Brake System (ABS) Control Module Brand	Network
Perodua	U0121	ABS/VSC fault Brand	Network
Peugeot	U0121	Lost Communication With Anti-Lock Brake System (ABS) Control Module SAE	Network
Porsche	U0121	Lost Communication With Anti-Lock Brake System (ABS) Control Module SAE	Network
Proton	U0121	ABS/ASC CAN timeout Brand	Network
Saab	U0121	Lost Communication With Anti-Lock Brake System (ABS) Control Module Brand	Network
Maxus (SAIC)	U0121	Lost Communication With BSD Brand	Network
MG (SAIC)	U0121	ABS CAN node absent Brand	Network
Smart	U0121	Lost Communication With Anti-Lock Brake System (ABS) Control Module SAE	Network
Sprinter	U0121	Lost Communication With Anti-Lock Brake System (ABS) Control Module SAE	Network
Suzuki	U0121	Lost Communication With ABS / ESPControl Module – Missing Message Brand	Network
SWM Motor	U0121	communication with ABS control module lost Brand	Network
Tata	U0121	Lost Communication With Anti-Lock Brake System (ABS) Control Module Brand	Network
Toyota	U0121	Communication with Anti-lock Brake System (ABS) lost Brand	Network
Volkswagen	U0121	No Communication with ABS Brake Control Module Brand	Network

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 7

These 7-character codes are manufacturer-specific variants of U0121 and may be reported by some scan tools.

Brand	Code	Description	System
Mercedes-Benz	U012100	Timeout ABR Brand	Network
SsangYong	U012100	CAN communication: Anti-lock Brake System (ABS)/Electronic Stability Control (ESC) message not received Brand	Network
Mercedes-Benz	U012102	P-Anforderung durch Bremsensteuergerät empfangen Brand	Network
Mercedes-Benz	U012182	No description available	Network
Mercedes-Benz	U012187	Die Kommunikation mit ESP hat Funktionsstörung. Botschaft fehlt. Brand	Network
SsangYong	U012187	CAN communication: Airbag Control Unit (ACU) message not received Brand	Network
Mercedes-Benz	U0121FB	Timeout Error SCCM (SCCM_Sw_Stat_AR2) Brand	Network

6Related codes

Browse Uxxx codes or U012xx codes.