Fuel level inconsistencies can be frustrating, especially after what appears to be a proper installation. If your CiES fuel senders are showing erratic or unreliable readings, here are the top five causes — and how to resolve them quickly and safely.
1. Grounding Issues
Most common cause of erratic readings.
Every CiES sender uses a black ground wire. If this wire isn’t properly grounded to a clean airframe location, the signal may float or fluctuate.
How to check:
- Use a long test lead to measure resistance from the black wire to a known good ground, such as the battery’s negative terminal.
- The resistance should be < 1 ohm. If higher, clean the contact point or relocate the ground wire.
2. Inconsistent Power Supply
Using 5VDC or 12VDC outputs from your instrument panel might seem convenient — but it’s not compliant with STC SA02511SE. CiES fuel senders must be powered via a dedicated circuit breaker on the aircraft bus.
Why this matters:
- Provides stable, regulated power
- Avoids signal noise from shared instrument circuits
- Meets FAA installation requirements
3. Loose or Missing Bladder Clips
In bladder-style fuel tanks, loose clips allow the rubber bladder to sag and rest on the sender float. As the aircraft vibrates in flight, the bladder moves against the float, creating spurious readings.
Solution:
- Ensure no contact between the float arc and the bladder
- Inspect bladder integrity
- Replace any broken or missing clips
4. Clogged Vent Lines
A partially blocked tank vent can trap air in the bladder as fuel drains, causing it to lift and touch the float. This usually happens at lower fuel levels, and may present as:
- Sudden spikes or jumps
- Increasing fuel level during flight
- Erratic behavior below half tanks
Fix: Clean or replace the vent line. It’s a simple check with big results.
5. Poor Connector Engagement
If you’re using plugs or multi-pin connectors, it’s possible a pin was pushed back during installation. Even soldered joints can fail due to cold solder or vibration fatigue.
What to do:
- Recheck any solder joints if applicable
- Unplug and inspect all connectors
- Verify that all pins are properly seated
Still Seeing Odd Behavior?
Contact our tech support team at (541) 977-1043.
We’ll walk you through advanced diagnostics and help get your system back on track.
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About CiES Inc.
Established in 2012, CiES is now the largest supplier of aviation fuel quantity probes and senders. They are the recognized leader in the design, development, certification, and manufacture of electronic sensor solutions for original equipment manufacturers, as well as direct-to-market consumer products. Through the creative application of cutting-edge technologies, CiES creates complex end-to-end solutions. This is a company that is changing the game in aviation technology and revolutionizing the way we navigate the skies. Aiming at future growth and innovation, CiES is pushing the boundaries of what is possible.
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