Trimble ERR021 Error: What It Means and How to Fix It

Applies to: R8, R10, SPS986, R12

What Does ERR021 Mean?

ERR021 on Trimble GPS receivers means the connection to a VRS (Virtual Reference Station) or NTRIP correction network has timed out. Network RTK relies on a cell or internet connection to a correction server — when that connection drops or the server stops responding, ERR021 appears and RTK positioning is lost.

Network RTK is convenient but depends on cellular coverage and server availability. In areas with marginal cell coverage, ERR021 can occur repeatedly during a session. The fix is either to restore the connection or switch to a local base station setup that doesn't depend on cellular.

Common Causes of ERR021

• Cellular signal lost or too weak to maintain the data connection to the correction network
• VRS/NTRIP provider server outage or maintenance
• Account credentials expired or data plan exhausted
• Rover moved outside the VRS network coverage area
• Network congestion causing the connection to time out

How to Fix Trimble ERR021 — Step by Step

1. Check cellular signal strength on the survey controller. Move to higher ground or a more open area if signal is marginal.
2. Try reconnecting to the NTRIP caster from Trimble Access: Survey > Rover Options > Network RTK > Connect.
3. Verify account credentials and data plan are active with the correction service provider.
4. Check if the correction service has a status page or outage notification — some providers post real-time service status.
5. If cellular is consistently unreliable in this area, set up a local UHF base station rather than relying on network RTK.
6. Try switching to a different mount point on the same NTRIP caster — some mount points may be more reliable than others.

When to Send It In for Service

ERR021 is a network/connectivity issue, not hardware. No service required unless the rover's internal cellular modem has failed, which would require service center repair.

Preventing ERR021 in the Future

Test cellular coverage in the project area before mobilizing equipment. Subscribe to a correction service with good coverage in your region. Keep local UHF radio RTK capability available as a backup for network-dependent setups.

Related Error Codes

Trimble Gps Error Err001 | Trimble Gps Error Err005 | Trimble Gps Error Err020