U1000

Class 2 Communication Malfunction

Car Fault Codes Chevrolet Network

Can you still drive? With care, short trips only

Who can fix it? Needs a workshop

Typical repair time 1 hour – 5 hours

Typical cost SAR 150 to 3,000

What it means

This is a Chevrolet (GM) manufacturer-specific code, and the same number can mean something different on other makes. Class 2 is GM's serial data network, a single-wire bus that modules use to exchange messages. This code means a module did not receive the expected messages from another module on this bus, and it is usually stored with other communication codes that identify the missing module.

Models covered: Chevrolet (GM) models with the Class 2 serial data network, mainly around 1996–2007.

Symptoms4

Some gauges stop working or several warning lights come on together.
The scan tool cannot communicate with some or all modules.
Starting problems if theft deterrent messages are affected.
Intermittent faults in various electrical functions.

Possible causes5

A weak battery, poor terminals or low voltage.
A failed or wet module pulling down the data line and disabling the whole bus.
An open or short in the data wire, or corrosion at the central network splice point.
A poor power feed or ground to one module.
Aftermarket accessories such as a stereo or tracker connected to the data line.

How to diagnose5

Check the battery, terminals and charging voltage first.
Scan all modules with a GM-capable tool to see which ones do not respond.
Check the data line at the diagnostic connector with a meter or scope and compare its behavior with the manufacturer specification.
Unplug modules or accessories one at a time; if communication returns, the last one unplugged is the culprit.
Inspect the central splice point and connectors for corrosion or water.

How to fix5

Charge or replace the battery and clean the terminals.
Disconnect aftermarket accessories tied into the data line.
Repair the data wire, connectors or damaged splice point.
Repair the module power or ground, then replace and program a faulty module if needed.
Clear codes in all modules and confirm they all communicate again.

Repair cost

0–500

500–2,000

2,000–5,000

5,000+

In Saudi riyals; the highlighted part is the expected range for this fault.

A battery or connector repair keeps the cost low, while replacing and programming a failed module pushes it to the top of the range.

Prices are rough estimates for common cars at independent workshops and vary with the car and the source of the part.
Prices last updated: September 2026

Frequently asked questions

Why do many modules fail at once?

Class 2 is one shared wire. If a faulty module pulls it down or it breaks at the splice point, many modules lose communication together.

Can an added accessory cause this code?

Yes, sometimes. Aftermarket devices tied into the data line can disturb the bus, so unplugging them is one of the first checks.

Is it different from generic CAN codes?

Yes. Class 2 is an older single-wire network, while CAN networks on newer vehicles use two wires, so the test methods differ.

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This guide is for information only and does not replace an inspection by a qualified technician. If the fault involves brakes, steering, engine temperature, electrics or refrigerant, do not attempt the repair yourself.

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