NetworkU1204

Serious

Severity: Serious - have it checked soon

Loss of serial communications for class 2 devices

21 brands affected · Description from GM data.

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

1What it means in plain English

Control modules in the car cannot communicate with each other over the vehicle network.

2Common causes

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

3Can I drive?

Serious · drive with care

The car may run normally or may not run at all. If the module that has lost communication controls steering, brakes, park brake, charging or engine cooling, drive only if those systems feel normal; stop safely if the steering becomes heavy, a brake warning appears, or the engine temperature climbs. If the car will not start or runs badly, have it towed.

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 21

Brand	Code	Description	System
Mercedes-Benz	U1204	No description available	Network
BYD	U1204	SAS message counter error Brand	Network
Chery	U1204	SAS message counter error Brand	Network
Daewoo	U1204	Loss of serial communications for class 2 devices Brand	Network
DFFS	U1204	PCAN configurations are the same Brand	Network
DFFX	U1204	SAS message counter error Brand	Network
EOBD	U1204	SAS-berichttellerfout Brand	Network
Geely	U1204	SAS message counter error Brand	Network
GM	U1204	Loss of serial communications for class 2 devices Brand	Network
Great Wall	U1204	SAS message counter error Brand	Network
Hafei	U1204	SAS message counter error Brand	Network
Honda	U1204	PGM-FI ECU Communication Error (Second Bus) (OTA Management Unit) Possible Fault Location and Cause PGM-FI ECU Fault CAN1H/CANH2 Line Disconnection CAN1L/CANL2 Line Disconnection Internal Fault Brand	Network
Isuzu	U1204	No description available	Network
Mahindra	U1204	No description available	Network
Mitsubishi	U1204	SAS message counter error Brand	Network
Peugeot	U1204	No description available	Network
Proton	U1204	SAS message counter error Brand	Network
Saab	U1204	Loss of serial communications for class 2 devices Brand	Network
MG (SAIC)	U1204	SAS message Counter Error Brand	Network
Smart	U1204	No description available	Network
Sprinter	U1204	No description available	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 4

These 7-character codes are manufacturer-specific variants of U1204 and may be reported by some scan tools.

Brand	Code	Description	System
Mercedes-Benz	U120400	Die Kommunikation mit dem Steuergerät 'Nachtsicht-Assistent' hat Funktionsstörung. Brand	Network
SsangYong	U120400	I2C communication: address error Brand	Network
Mercedes-Benz	U120402	General Signal Failure Brand	Network
Mercedes-Benz	U120487	Communication with control unit 'Night View Assist' has a malfunction. Missing Message. Brand	Network

6Related codes

Browse Uxxx codes or U120xx codes.