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No oil pressure after Oil Purge on a 912 IS

mhailey

mhailey

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I’m not sure if this is a Rotax or a G3 X question. In the purge procedure we’ve gone through that and we get to the point where you spin the prop to look for oil pressure but we have none. Obviously master is on G3X’ is powered. But why is the oil pressure still X? Is there something I’m missing? My buddy is kind of starting to look at me funny after he’s spun the prop a hundred times. IMG_6911.jpeg
 
Do you have Lane B turned on? It powers the oil pressure and temperature sensors.
 
By the way I’m waiting on new placards after an avionics upgrade and powder coating of the panels.
 
It was working fine during the pre-run up prior to starting the Condition Inspection. I suppose we could have bumped something. Is the sensor easily accessible ?
 
mhailey said:
Are we talking about the using this switch View attachment 97684
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Not that switch, that is backup power for the EFIS. That switch brings a separate battery on-line.

At the bottom of the center console area is a different backup battery switch. This switch does not actually connect to a backup battery, it uses the main battery to power the ECU. Otherwise the ECU is only powered up when the generators is online (engine running) or start-power is enabled by turning the start key.
 
mhailey said:
It was working fine during the pre-run up prior to starting the Condition Inspection. I suppose we poo
N8DAV8R said:
Not that switch, that is backup power for the EFIS. That switch brings a separate battery on-line.

At the bottom of the center console area is a different backup battery switch. This switch does not actually connect to a backup battery, it uses the main battery to power the ECU. Otherwise the ECU is only powered up when the generators is online (engine running) or start-power is enabled by turning the start key.
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could have bumped something. Is the sensor easily accessible ?
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Loop as ok I I
 
mhailey said:
It was working fine during the pre-run up prior to starting the Condition Inspection. I suppose we could have bumped something. Is the sensor easily accessible ?
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Looks like the oil pressure sensor is below the starter. ref. MMH 76-50-00 p. 14

OPS.png
 
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OMG!!! The oil pressure works only when the air sensor in the air box is connected! I have the lower cowling off, obviously doing my condition inspection. So I have the air sensor disconnected and laying with the cowling to the side. I was getting a lane a fault light but I just assumed it was because of the air sensor. The picture is without the back up battery switch being turned on. Just normal configuration of master on lane a and lane B on. image.jpg
 
snowsam said:
Wow.

Did you know that you can view basic lane fault info from the status screen in the g3x?
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I actually do know and have used that ability. I had been asking Grok if it had any ideas, and when I told it the story it gave this explanation:

Why the Disconnected O2 Sensor Affects Oil Pressure Display​


The O2 sensor isn't directly tied to oil pressure mechanically, but in the integrated G3X setup for the RV-12 iS, sensor faults can propagate through the system's data buses or fault logic:


  1. Shared Data Bus (CAN Bus) Interdependency:
    • The Rotax 912 iS ECU communicates engine data (including O2 sensor inputs) to the G3X via the CAN bus (Controller Area Network). The GEA 24 (Engine/Airframe Unit) processes this alongside analog sensors like oil pressure (e.g., Kavlico P4055, wired to GEA 24 pins 8/9/10).
    • A disconnected O2 sensor triggers an ECU fault code (e.g., P0130 for O2 circuit malfunction, per Rotax diagnostics). This can flag the entire EIS (Engine Indication System) as unreliable, causing the G3X to suppress or "X out" related readings like oil pressure to avoid displaying potentially inaccurate data during a fault state.
  2. G3X Fault Handling:
    • The G3X Touch (software version-dependent) uses error suppression logic: If it detects a critical engine sensor fault (O2 is considered key for EFI tuning), it may disable non-essential but related displays like pressures until resolved. This is a safety feature to prevent false alarms or misleading info.
    • In RV-12 iS installations, the O2 sensor's wideband output (0.5–4.5V signal) is routed through the engine harness to the ECU, then to the G3X. Disconnection mimics a wiring fault, cascading to EIS outputs.
  3. RV-12 iS Specifics:
    • The air intake box (part of Van's filtered air system) houses the O2 sensor bung (typically a threaded M18x1.5 port) on the exhaust side for sampling. Van's POH (Pilot's Operating Handbook, Section 7) and Rotax Installation Manual (IM-912, Section 21) confirm this location to ensure accurate post-combustion readings without intake interference.
    • Forum reports (e.g., Van's Air Force) note similar G3X quirks where EFI-related faults (like O2 or fuel pressure) cause cascading "red X" on pressures, often due to CAN bus glitches or unconfigured sensors.

This explains why the purge procedure worked mechanically (no actual oil system issue), but the display failed—it's a G3X/ECU interaction, not a Rotax oil pump problem.
 
This didn't jive with what I remembered about leaving the AATPS sensor disconnected.

I just started an oil change and I disconnected the sensor.. here's what I got (Lane A error light illuminated, not pictured) I think you have a loose wire/connector on your oil pressure sensor.
 

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mhailey said:
OMG!!! The oil pressure works only when the air sensor in the air box is connected! I have the lower cowling off, obviously doing my condition inspection. So I have the air sensor disconnected and laying with the cowling to the side. I was getting a lane a fault light but I just assumed it was because of the air sensor. The picture is without the back up battery switch being turned on. Just normal configuration of master on lane a and lane B on. View attachment 97687
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It seems fairly common that RV 12 owners do not refer to the maintenance manual that is supplied with the airplane when they do maintenance.
The way the firewall forward system is designed, the induction air temperature sensor doesn’t need to be disconnected to remove the lower cowling (or the SCAT hose between the air filter and the throttle body).
The intended method is to use a very long, number two Phillips screwdriver and loosen the four screws in the top plate of the induction airbox.
Then unpin the lower cowl and lower it downward. This will leave the air filter and top plate assembly hanging by the scat hose and won’t require you to disconnect the inlet air temperature sensor.
Repeatedly connecting and disconnecting that sensor is less than ideal for its longevity, and you won’t ever have this issue of no oil pressure displayed.
 
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rvbuilder2002 said:
It seems fairly common that RV 12 owners do not refer to the maintenance manual that is supplied with the airplane when they do maintenance.
The way the firewall forward system is designed, the induction air temperature sensor doesn’t need to be disconnected to remove the lower cowling (or the SCAT hose between the air filter and the throttle body).
The intended method is to use a very long, number two Phillips screwdriver and loosen the five screws in the top plate of the induction airbox.
Then unpin the lower cowl and lower it downward. This will leave the air filter and top plate assembly hanging by the scat hose and won’t require you to disconnect the inlet air temperature sensor.
Repeatedly connecting and disconnecting that sensor is less than ideal for its longevity, and you won’t ever have this issue of no oil pressure displayed.
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I agree. If I had left the sensor connected this would have never happened. It is certainly a pain to disconnect that connector. As it worked out I had one of the screws frozen, so I didn't really want to work on that screw with the cowl on. This is the first Condition Inspection, and out of all panels I ended up with 5 screws requiring much cussing, and tools to get loose. I'm not the builder, but I wish someone had used a little ant-seize or at least some oil!
 
Fair point about the connector, but those screws are kind of a pain to remove and replace due to the poorly spec'ed air filter and air box. The screws are under tension because of the filter being smashed in. It's much easier to just undo the connector and scat tube.
 
N8DAV8R said:
Fair point about the connector, but those screws are kind of a pain to remove and replace due to the poorly spec'ed air filter and air box. The screws are under tension because of the filter being smashed in.
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:unsure: Mine fits just fine - is your plate all the way up to the body of the filter?
 
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jrtens said:
:unsure: Mine fits just fine - is your plate all the way up to the body of the filter?
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The filter is too long, it's a common problem. As I understand things there was a change to the filter at some point in the past. Older ones fit, later ones don't.
 
N8DAV8R said:
The filter is too long, it's a common problem. As I understand things there was a change to the filter at some point in the past. Older ones fit, later ones don't.
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Common ??? I don't recall reading about it. Can you reference another post please.
 
jrtens said:
Common ??? I don't recall reading about it. Can you reference another post please.
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I had the same problem during my build. The K&N filter supplied with my powerplant kit was slightly too long, making it very difficult to get the four screws into the airbox.
 
jsalley said:
I had the same problem during my build. The K&N filter supplied with my powerplant kit was slightly too long, making it very difficult to get the four screws into the airbox.
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When did you receive your powerplant kit? The K&N RU-0800 filter I received last September was normal. I am wondering if the one you received was not an RU-0800.
 
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jrtens said:
When did you receive your powerplant kit? The K&N RU-0800 filter I received last September was normal. I am wondering if the one you received was not an RU-0800.
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Received this past January. The filter is the RU-0800. I’m guessing the filter itself is the issue; I don’t think Van’s would have changed the airbox dimensions in the finish kit.
 
jrtens said:
Common ??? I don't recall reading about it. Can you reference another post please.
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I've talked with a number of other builders with the same situation, and Van's is aware of this as well. They say to just smash the filter into place.

I don't wear my circus monkey suit on the weekends so I'm not going to find posts for you. I'm perfectly fine with you not believing me.
 
mhailey said:
I actually do know and have used that ability. I had been asking Grok if it had any ideas, and when I told it the story it gave this explanation:

Why the Disconnected O2 Sensor Affects Oil Pressure Display​


The O2 sensor isn't directly tied to oil pressure mechanically, but in the integrated G3X setup for the RV-12 iS, sensor faults can propagate through the system's data buses or fault logic:
Click to expand...

Grok is full of crap! The Rotax 912iS in the RV-12 doesn't have an O2 sensor.

It does have an AAPTS (Ambient Air Temperature and Pressure Sensor) is an electronic sensor for the engine's fuel-injected models, like the 912iS, that measures the outside air's temperature and pressure to provide this critical data to the Engine Control Unit (ECU) for accurate fuel mixture control.
 
Tony Kirk said:
Grok is full of crap! The Rotax 912iS in the RV-12 doesn't have an O2 sensor.

It does have an AAPTS (Ambient Air Temperature and Pressure Sensor) is an electronic sensor for the engine's fuel-injected models, like the 912iS, that measures the outside air's temperature and pressure to provide this critical data to the Engine Control Unit (ECU) for accurate fuel mixture control.
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Right.. but back to my post (#17).. disconnecting that sensor doesn't kill the Oil Pressure readings.
 
rcarsey said:
Right.. but back to my post (#17).. disconnecting that sensor doesn't kill the Oil Pressure readings.
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I agree that typically it just lights one of the Lane warning LEDs, but in a couple of instances I have seen other displayed issues but I can't remember any specific details so I wasn't going to say for sure that it wouldn't cause it.
 
rcarsey said:
Right.. but back to my post (#17).. disconnecting that sensor doesn't kill the Oil Pressure readings.
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Sorry Rob, I've got top cowling back on, so I can't easily get to the connector, or I would test what happened again. I'll try to duplicate the issue when next I have the cowl off. By the way I'm also going to order one of those slightly shorter Air Filters. Mine was a bear getting back in. I took my scope and took a few pictures.IMG_6920.JPGIMG_6921.JPG
 
Rob I am changing oil today, so I thought I might try this Oil Pressure thing again. I have the top cowling off, and have access to the connector. With Master On, Both Lane switches on, I have an Oil Pressure Gauge reading zero. I then walked around, and disconnected the sensor, When I came back to the screen I have an X on the Oil Pressure. I then go back up front and reconnect the sensor. I come back and the Oil Pressure is still X. I recycled the Lane switches, and the X goes away, and Oil Pressure has a reading of Zero again. I'll post a pic of the X versus Oil pressure reading, so those that aren't familiar with the Garmin G3X Touch can see the difference. I didn't build, so I don't know if this is a wiring issue, but it definitely does do it!
rcarsey said:
IMG_7167.JPGIMG_7166.JPG
Right.. but back to my post (#17).. disconnecting that sensor doesn't kill the Oil Pressure readings.
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mhailey said:
Rob I am changing oil today, so I thought I might try this Oil Pressure thing again. I have the top cowling off, and have access to the connector. With Master On, Both Lane switches on, I have an Oil Pressure Gauge reading zero. I then walked around, and disconnected the sensor, When I came back to the screen I have an X on the Oil Pressure. I then go back up front and reconnect the sensor. I come back and the Oil Pressure is still X. I recycled the Lane switches, and the X goes away, and Oil Pressure has a reading of Zero again. I'll post a pic of the X versus Oil pressure reading, so those that aren't familiar with the Garmin G3X Touch can see the difference. I didn't build, so I don't know if this is a wiring issue, but it definitely does do it!
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I was just thinking of you a couple days ago. I had my cowl off and did this same test. I can confirm. If I turn the Lanes ON while the AATPS sensor is disconnected.. I get the red X. If I turn the Lanes ON while its connected, all is happy. You usually can't undo the X by simply plugging in the sensor. You need to recycle the Lanes (probably just the lane that controls the oil pressure).
 
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