Topcon ERR-04 Error: What It Means and How to Fix It

Applies to: HiPer HR, HiPer V, HiPer II

What Does ERR-04 Mean?

ERR-04 on Topcon HiPer GPS/GNSS receivers means the correction data link between the base station and rover has been interrupted. RTK positioning requires a continuous stream of correction data from a reference station — either a local base or an NTRIP network. When this correction stream stops or degrades beyond usable quality, the receiver loses its RTK fixed solution and displays ERR-04. Without corrections, the rover can only produce autonomous (meter-level) or float-mode positions that are unsuitable for most survey and construction work.

The HiPer HR and HiPer V support multiple correction data paths: internal UHF radio modem, cellular data (via Topcon's SIM or external hotspot), and Bluetooth relay from a data collector. Each path has different failure modes. UHF radio is range-limited and terrain-sensitive; cellular depends on data coverage in the field; Bluetooth has range and pairing limitations. Identifying which link failed is the first step in fixing ERR-04.

A key characteristic of ERR-04 is that it can be intermittent — corrections drop for 10-30 seconds, positions go to float, then corrections return and the receiver re-initializes. This intermittent pattern is often caused by radio frequency interference, terrain blocking a radio link at certain rover positions, or cellular network congestion. Consistent ERR-04 is usually a configuration or hardware issue; intermittent ERR-04 is usually environmental.

Common Causes of ERR-04

• UHF radio range exceeded — the rover has moved outside the effective range of the base station's radio transmitter (typically 1-5km depending on terrain and antenna height)
• Terrain blocking the UHF radio link — line-of-sight interruption from a hill, building, or dense vegetation between base and rover
• Cellular data link failure — no network coverage at the rover location, SIM card issue, or NTRIP caster is offline
• Base station powered off, battery died, or was accidentally moved during the survey
• NTRIP mount point service interruption — the correction network is experiencing downtime or the mount point closest to the project has gone offline
• UHF frequency conflict — another radio on the same frequency in the area is causing interference with the correction data stream

How to Fix Topcon ERR-04 — Step by Step

1. Check the correction age in MAGNET Field. A correction age of 999 or '--' means no corrections are arriving. A correction age steadily climbing above 10 seconds means corrections are arriving but intermittently.
2. For UHF radio link: verify the base station is still active, the radio antenna is connected, and the base hasn't been disturbed. Move the rover to a higher elevation or closer to the base to test if range is the issue.
3. For cellular/NTRIP: check data connectivity on the field controller. Open a browser to confirm internet access. If no internet, move to an area with cellular coverage or switch to a local base.
4. Verify the NTRIP caster address, port, mount point, and credentials in MAGNET Field. Incorrect settings or expired credentials are a common cause after setup changes.
5. Check the base station battery if using a local base. A base station that powers off mid-survey causes ERR-04 on all rovers without warning.
6. Switch correction paths if available — if UHF is failing, try cellular NTRIP. If NTRIP is down, try UHF from the local base.
7. If corrections were working and stopped suddenly, check if the base station moved. Even a small movement or disturbance of the base during a survey will corrupt all collected data — the entire survey is suspect and the base needs to be re-centered and corrections verified.
8. Re-initialize the RTK fix after restoring the correction link. In MAGNET Field: tap the solution status indicator and select 'Re-Initialize RTK'.

When to Send It In for Service

ERR-04 is almost always a link, network, or configuration issue rather than a hardware problem. If the radio modem on the HiPer itself has failed (transmit/receive indicator on the web interface shows no activity despite confirmed base transmission), the modem may need service. Internal UHF modem replacement is a service center repair.

Preventing ERR-04 in the Future

Plan base station placement to maximize radio coverage of the work area. Keep base station batteries topped off with backup power available. For critical work, have a secondary correction source configured (e.g., NTRIP as backup to local UHF). Monitor correction age in MAGNET Field continuously — don't wait for ERR-04 to notice a degrading link.

Related Topcon GNSS Error Codes

Topcon Gnss Error Err03 | Topcon Gnss Error Err01 | Topcon Gnss Error Err05