U049B: Invalid Data Received From Tachograph Module

What it means

A control module received invalid data from the tachograph module. The code identifies a data validity fault; the specific affected function depends on the vehicle.

At a glance

• Usually lights the warning light of the system that lost communication

How it works

The tachograph module records and reports vehicle-operation data, and shares status with other modules over the network. U049B sets when another module receives data from the tachograph but judges it invalid; it does not necessarily mean the tachograph has stopped recording.

Common causes

Most likely first.

1. Fault in the transmitting module
2. Network wiring or connector fault
3. Module power or ground fault
4. Software or configuration mismatch

Symptoms

• Tachograph functions may not work correctly
• Related communication codes or system warnings may appear

How to diagnose it

1. Use a scan tool to save freeze-frame details and check whether U049B returns, since a transient network problem may have set it.
2. Check for companion tachograph and network codes and verify whether the tachograph itself displays a fault or interruption.
3. Inspect tachograph connectors and network wiring for loose pins, corrosion, damage, or chafing.
4. Check tachograph power and ground using the manufacturer's diagnostic procedure, because supply faults can affect the messages it sends.
5. If wiring and supplies are sound, use vehicle-specific tests to assess tachograph communication and verify software and configuration.

Common fixes

• Reconnect or clean a loose or corroded tachograph connector.
• Repair damaged network wiring to the tachograph.
• Repair a poor tachograph power or ground connection.
• Correct software or configuration if vehicle-specific service information requires it.
• Replace the tachograph module if testing confirms it is faulty.

Can I keep driving?

Tachograph data or related functions may be unreliable, so follow applicable operating and recordkeeping requirements until it is checked. This code alone does not normally indicate an engine fault, but address any accompanying vehicle warnings.