I've been struggling with a GSU 73 problem for over a year now and Garmin has gone silent on me. I'm hoping people here can either (1) help me figure out how to get real help from Garmin or (2) help me track down this problem on my own. Here is email I sent to Garmin support back in January but I haven't heard anything back from them yet.
We are still having issues with our GSU 73 that started Feb 2025 after 12 years and 1300 flight hours with no issues. We have gone through the RMA process three times now. We need to figure out how to properly diagnose the problem and get this resolved. I need guidance on how to proceed.
Here is the history, starting from right now and going backwards in time. Long story short:
The problem continued on my most recent two flights. In the first flight, the altitude, airspeed, VS, and OAT were all X'd out until about 20 minutes into the flight. For the next 10 minutes, it was intermittently working, slowly working more and more often. By about 30 minutes it stopped having an issue and worked fine for the rest of the 2hr flight.
On the next flight I was departing from a Class C so by the time I got into the air the plane had already been running for about 15 minutes. By about 5min into the flight it started working partially. About ten minutes later it stopped failing.
Note that in both cases it was fully broken for about 20 minutes, then about 10 minutes of intermittently working. But in one case we spent most of that 20 minutes on the ground. Note that we have also seen the same pattern in the hangar without the engine running or the plane moving.
Here is a video of the most recent issue:
https://www.dropbox.com/scl/fi/elyd...6.39.mp4?rlkey=kx6cohmxdife8n32s78fdxwx6&dl=0
Also note:
The GSU73 intermittently fails on the ground and in flight. At first, it almost constantly fails, spending more time in a failed state than in a working state. But over time it gradually fails less often failed and spends more time working. After about 20 minutes, it works almost 100% of the time, but will still fail occasionally.
Important: this happens in the air but also in the hangar on the ground with the engine shut off.
When I say fail, this is what I mean:
After the GSU 73 had been working for a while (since June 2025) we started seeing the air data failures during flight (airspeed, altitude, VS, TAS, OAT). We replaced the unit through the RMA program. Since that replacement (from October until today) we have had the exact same issues with the air data but additionally after the replacement we started intermittently losing all data from the unit as previously described.
June 2025
Ever since we replaced the unit April 2025 we had occasional complete losses of all data from the GSU 73. Most of the time it would come back online but on at least one occasion it remained offline for the duration of the flight. We were able to reproduce the issue on the ground with the top connector clamshell open. When the config card was slightly pushed it would cause the GSU 73 to fail. When the pressure was released the GSU 73 would work again. We were able to completely and reliably cause the GSU 73 to work and not work just by gently touching the config module.
So we replaced the config module and the wiring harness with a new one. All problems went away for the next few months.
March 2025
Here is the email I sent back in March that led to us replacing the GSU 73 in April.
Since replacing the GSU 73 through this RMA, we have made several flights with the aircraft. We had no issues on two short test flights, but the new GSU 73 has rebooted during two of the three longer flights since it was replaced. When the reboot happened, we temporarily lost all ADAHRS and engine indication data, and then the display showed an "ADAHRS Align" screen (again, during flight).
I was flying during the last reboot which occurred yesterday, Mar 23, at about 2PM EDT. Here is a timeline for that flight:
For about the first 30min of the flight, there were no issues at all
For about the next 60min of the flight, oil pressure readings were inconsistent, varying between a normal pressure and a low pressure. I have several videos showing this behavior.
Then the GSU 73 rebooted. For the final 30min of the flight there were no issues at all
Although it is possible it is an issue with the oil pressure sensor, that doesn't explain the GSU 73 reboots. It also wouldn't explain why the reboot instantly caused the oil pressure to start reading correctly again. I think there may be something wrong with the new GSU 73 causing the reboots and possibly it also affected the oil pressure. Note that we never had any reboots with the original GSU 73.
I also wanted to mention that during the ~60 minutes of mostly inaccurate oil pressure readings, where it swung from low to normal, the lows trended downwards.
February 2025
Here is the email that the builder sent in February that led to our original RMA replacement.
I have a older G3X non-touch with GSU 73
Have been flying 12 years and 1300 hours with no real issues.
3 flights ago for 1/2 of one flight got erroneous oil pressure indications. (Steady in the 70s, then 0, red X, then in 20’s for a bit, then back into the 70’s for rest of flight (15 min of erroneous indications, then 10 min of normal).
next several flights (~10 hr of flight time) all normal indications.
Today during ground run all was normal, but soon after takeoff in IMC All EGT and CHT temps were bouncing all over the place (synchronized at first, all 6 cyld together). Going to red-line , then normal, then to 0, then back to normal. Most aberrations were for 1-3 seconds at a time. (Oil pressure and all other instruments at this time were steady and correct). I opted to continue flight as with engine sound, power was sure it was an instrument issue and not something actually happening. At this time I assumed I had a ground fault of some sort.
Later in the flight, it got weirder, with fuel indications (1 tank at a time) going to 0, then back up, oil pressure going all over the place, single or 2 cylinders showing erratic temperatures, and also sometimes all 6 cylinders temp readings bouncing together.
Also some jumps in RPM which were not happening.
We are still having issues with our GSU 73 that started Feb 2025 after 12 years and 1300 flight hours with no issues. We have gone through the RMA process three times now. We need to figure out how to properly diagnose the problem and get this resolved. I need guidance on how to proceed.
Here is the history, starting from right now and going backwards in time. Long story short:
- We think the problem from back in Mar 2025 was actually the config card the whole time and our original GSU 73 was just fine. We replaced the config module in Jun 2025.
- The RMA units we received in April and again in October seem to be having issues not related to the config module.
- We are out of any theories as to what is causing our current issues and we need guidance on next steps.
The problem continued on my most recent two flights. In the first flight, the altitude, airspeed, VS, and OAT were all X'd out until about 20 minutes into the flight. For the next 10 minutes, it was intermittently working, slowly working more and more often. By about 30 minutes it stopped having an issue and worked fine for the rest of the 2hr flight.
On the next flight I was departing from a Class C so by the time I got into the air the plane had already been running for about 15 minutes. By about 5min into the flight it started working partially. About ten minutes later it stopped failing.
Note that in both cases it was fully broken for about 20 minutes, then about 10 minutes of intermittently working. But in one case we spent most of that 20 minutes on the ground. Note that we have also seen the same pattern in the hangar without the engine running or the plane moving.
Here is a video of the most recent issue:
https://www.dropbox.com/scl/fi/elyd...6.39.mp4?rlkey=kx6cohmxdife8n32s78fdxwx6&dl=0
Also note:
- No issues with engine indication, so that part of the GSU 73 remained working the entire time
- No ADAHRS align came up during flight
- This tells me this is not a power problem. If it was, we'd see everything go offline when it rebooted.
The GSU73 intermittently fails on the ground and in flight. At first, it almost constantly fails, spending more time in a failed state than in a working state. But over time it gradually fails less often failed and spends more time working. After about 20 minutes, it works almost 100% of the time, but will still fail occasionally.
Important: this happens in the air but also in the hangar on the ground with the engine shut off.
When I say fail, this is what I mean:
- Sometimes, we lose all air data, specifically: altitude, airspeed, vertical speed, TAS, and OAT. Here is a video of this type of failure: https://www.dropbox.com/scl/fi/8cut...0.23.mp4?rlkey=6mf8v7ux0h0rr0t3l4kqze820&dl=0
- Other times, we lose all data from the GSU 73, including engine data. Here is a video of this type of failure: https://www.dropbox.com/scl/fi/gz73...0.26.mp4?rlkey=1kerrh332mas7hitzf76m8ynb&dl=0
- In config mode, we still get failures. Sometimes we see OAT toggle between valid and invalid but no other issues.
- Other times, in config mode, we see Hardware Status toggle between Fault and OK. Here is a video of this happening: https://www.dropbox.com/scl/fi/6frv...4.35.mp4?rlkey=uf7nd2ikp6isli35nzk3m7ssl&dl=0
- We have replaced the OAT sensor since it was being called out specifically as failed at times. That did not change anything.
- We have inspected the connectors and everything looks to be in great shape
- We have inspected the config card and it doesn't seem to be causing the problem (see below -- we previously had a problem with the config card and replaced it)
- We can't identify how this can be an electrical issue. The unit has multiple power and ground pins and is connected through a VPX. Per the config mode screen it doesn't seem that the device actually powers off, just toggles between failure/working states.
- As I mentioned, we have gone through the RMA process three times
After the GSU 73 had been working for a while (since June 2025) we started seeing the air data failures during flight (airspeed, altitude, VS, TAS, OAT). We replaced the unit through the RMA program. Since that replacement (from October until today) we have had the exact same issues with the air data but additionally after the replacement we started intermittently losing all data from the unit as previously described.
June 2025
Ever since we replaced the unit April 2025 we had occasional complete losses of all data from the GSU 73. Most of the time it would come back online but on at least one occasion it remained offline for the duration of the flight. We were able to reproduce the issue on the ground with the top connector clamshell open. When the config card was slightly pushed it would cause the GSU 73 to fail. When the pressure was released the GSU 73 would work again. We were able to completely and reliably cause the GSU 73 to work and not work just by gently touching the config module.
So we replaced the config module and the wiring harness with a new one. All problems went away for the next few months.
March 2025
Here is the email I sent back in March that led to us replacing the GSU 73 in April.
Since replacing the GSU 73 through this RMA, we have made several flights with the aircraft. We had no issues on two short test flights, but the new GSU 73 has rebooted during two of the three longer flights since it was replaced. When the reboot happened, we temporarily lost all ADAHRS and engine indication data, and then the display showed an "ADAHRS Align" screen (again, during flight).
I was flying during the last reboot which occurred yesterday, Mar 23, at about 2PM EDT. Here is a timeline for that flight:
For about the first 30min of the flight, there were no issues at all
For about the next 60min of the flight, oil pressure readings were inconsistent, varying between a normal pressure and a low pressure. I have several videos showing this behavior.
Then the GSU 73 rebooted. For the final 30min of the flight there were no issues at all
Although it is possible it is an issue with the oil pressure sensor, that doesn't explain the GSU 73 reboots. It also wouldn't explain why the reboot instantly caused the oil pressure to start reading correctly again. I think there may be something wrong with the new GSU 73 causing the reboots and possibly it also affected the oil pressure. Note that we never had any reboots with the original GSU 73.
I also wanted to mention that during the ~60 minutes of mostly inaccurate oil pressure readings, where it swung from low to normal, the lows trended downwards.
February 2025
Here is the email that the builder sent in February that led to our original RMA replacement.
I have a older G3X non-touch with GSU 73
Have been flying 12 years and 1300 hours with no real issues.
3 flights ago for 1/2 of one flight got erroneous oil pressure indications. (Steady in the 70s, then 0, red X, then in 20’s for a bit, then back into the 70’s for rest of flight (15 min of erroneous indications, then 10 min of normal).
next several flights (~10 hr of flight time) all normal indications.
Today during ground run all was normal, but soon after takeoff in IMC All EGT and CHT temps were bouncing all over the place (synchronized at first, all 6 cyld together). Going to red-line , then normal, then to 0, then back to normal. Most aberrations were for 1-3 seconds at a time. (Oil pressure and all other instruments at this time were steady and correct). I opted to continue flight as with engine sound, power was sure it was an instrument issue and not something actually happening. At this time I assumed I had a ground fault of some sort.
Later in the flight, it got weirder, with fuel indications (1 tank at a time) going to 0, then back up, oil pressure going all over the place, single or 2 cylinders showing erratic temperatures, and also sometimes all 6 cylinders temp readings bouncing together.
Also some jumps in RPM which were not happening.
