NetworkU1221

Serious

Severity: Serious - have it checked soon

Loss of serial communications for class 2 devices

14 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 14

Brand	Code	Description	System
Chery	U1221	Lost communication with Airbag Module Brand	Network
Daewoo	U1221	Loss of serial communications for class 2 devices Brand	Network
DFFS	U1221	Steering wheel torque signal invalid Brand	Network
EOBD	U1221	EPS CAN obrada Brand	Network
GM	U1221	Loss of serial communications for class 2 devices Brand	Network
Holden	U1221	Invalid Data Received From Power Steering Control Module Brand	Network
Honda	U1221	Invalid Data Received From DC-DC Converter Control Module Brand	Network
Maserati	U1221	Lost communication with left headlamp module - component internal fault Brand	Network
Mitsubishi	U1221	EPS CAN processing Brand	Network
Opel	U1221	Loss of serial communications for class 2 devices Brand	Network
Peugeot	U1221	No description available	Network
Proton	U1221	EPS CAN processing Brand	Network
Saab	U1221	Loss of serial communications for class 2 devices Brand	Network
Subaru	U1221	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 1

These 7-character codes are manufacturer-specific variants of U1221 and may be reported by some scan tools.

Brand	Code	Description	System
SsangYong	U122183	CAN communication: Instrument Cluster Module (ICM) checksum error (160) Brand	Network

6Related codes

Browse Uxxx codes or U122xx codes.