Fault Message:

TU6R - FUEL PROBE/WRG

Fault Code:

284465BPK

Associated CAS:

FUEL QTY DEGRADED
(Advisory)

TU6R FMQGS PLAIN PROBE/WRG FAULT shows on the CAIMS PMAT when the fuel quantity:

• Probe capacitance is out of range
• Probe circuit is open
• Probe circuit is shorted
• Probe is contaminated
• The Fuel Management and Quantity Gauging Computer (FMQGC) automatic calibration test failed (Circuit Fault)

• Fuel Quantity Probe (TU6R)
• Fuel Management and Quantity Gauging Computer (FMQGC) (A47)
• Associated Wiring

Advisory Wire/Service Bulletin:

• AW700-45-0065 - CAIMS Nuisance Fault Messages

Forum Articles/Infoservice/Newsletter: None

NOTE:

• FUEL QTY DEGRADED (Cyan) shows only when multiple sensors failures occur (compensators or more than 50% of the fuel probes in a tank failed)
• This fault has been seen in flight in certain cases, as the aircraft passes thru certain altitudes or the aircraft is in certain attitudes. Pay particular attention to coax connectors from FMQGC to fuel tank external disconnects. Before investing time de-fueling/stumping/venting inspect these runs first
• **Do not use a Megger Meter if fuel tank venting, or inside the fuel tanks

1. Fuel quantity indication symptom:
   Quick fuel quantity indication increase or decrease in a tank are symptoms of intermittent multiple probe failures typically due to water contamination or loss of excitation to multiple probes in a tank.
2. Fuel contamination and probe cleaning procedures:
   Sump the tanks if contamination is suspected, If water is evident in the fuel sample, the tank and probes must cleaned and ventilated. Probe can be cleaned using an alcohol bath to ensure that no water, foreign matter or oil is on the tubes. The exterior of the tubes may be wiped, if necessary, with a lint free paper or cloth towel. The interior of the tubes may be cleaned with a soft bristle brush. Probe tubes removed from the alcohol bath may be drip dried or blown off with dry compressed air. The operator must wear protective gloves during cleaning and lint free gloves whenever the tubes are handled after cleaning.
3. Multiple probe failure:
   When CAIMS is reporting two or more probes failures, which are powered by the same excitation power, suspect the common excitation wiring to be at fault. Most probable cause of a probe excitation failure is a loose, damaged or improperly assembled co-axial connector.Before opening the fuel tanks, the most effective method to troubleshoot an intermittent excitation failure is to monitor the probes capacitance value in CAIMS, or monitor the excitation voltage using a digital voltmeter while a second person checks for intermittent connection in the circuit outside the tanks. A sudden change in the capacitance or voltage value is an indication of a faulty connection or wiring. When measuring probe excitation power using a digital voltmeter, the excitation voltage should be approximately 5.3 VAC between the connector center pin and casing. Without a good shield return, the excitation voltage will typically be approximately 3.2 VAC or lower. Field experience and reliability data show that the FMQGC excitation output is the least probable cause of probe excitation failures. Most FMQGC removed for this failure mode are No Fault Found (NFF) during shop repair.
4. Single probe failure:
   If CAIMS reports a single probe failure repeatedly, suspect a loose terminal on the probe, the signal return wiring to the FMQGC, a probe water contamination or rarely, a failure of a single FMQGC input.
5. Intermittent FMQGC and re-racking procedure:
   Intermittent FMQGC issues are commonly caused by poor installation of the computer in the mounting tray. The FMQGC must be re-installed if movement of the unit or harness changes the failure symptoms. The FMQGC pins and mounting tray receptacle have minimal engagement tolerance. Furthermore, the special coaxial pins/sockets used for the fuel probe excitation circuit require additional force to fully engage them. Proper installation and racking of the FMQGC is vital to the operation of the fuel system. Also, check coaxial connectors pin/socket for proper friction and pushed back contacts.
   Install the FMQGC in its mounting tray as follows:

   1. Slide the FMQGC straight into the mounting tray until connectors engage.
   2. Engage the mounting tray turn buckles onto the front of the FMQGC.
   3. Screw in the turn buckles until the tension increase.
   4. Placing both hands on the front of the computer, push the FMQGC into the mounting tray.
   5. Repeat Step c and d several times until the turn buckles are tight and the FMQGC connectors are fully engaged.

6. Probe TU10R excitation power is provided by the FMQGC CH A, excitation C (#2). The ground return for the excitation is done through the coaxial cable braid wire, through the FMQGC when installed. Probe excitation C is used for a series of probes in the RH wing tank. The probes excitation is connected in parallel (daisy chain).
7. Coaxial connector repair instructions:

   • Coaxial connector repair
   • Crimp Procedure
   • Solder_Crimp Procedure

8. Electrical connections to the probe tank units are made via screw connections. The screws are captive to the tank unit and are sized in accordance with the following, in order to preclude mis-wiring.
   The terminal screws must be torque as follow:

   FUNCTION	SCREW SIZE	TORQUE
   Hi-Z	#8-32	22-27 IN-LB
   Lo-Z	#6-32	12-15 IN-LB
   Comp Lo-Z	#10-32	26-33 IN-LB

1. Using CAIMS, check for FMQGC Fault message.

   1. If FMQGS COMPUTER CH A AUTOCAL #2/WRG FAULT is displayed, go to step 17.
   2. If TU6R FMQGS PROBE COMP/WRG FAULT is displayed, go to step 13.
   3. If two or more probes faults are displayed, continue with next step.

2. Sump the tank, check for Water Contamination in the fuel, sample about 5 gallons or more (per tank) (If water is found in fuel sample, drain and access tank to clean).

   1. If system checks are good, do close out.
   2. If fault remains, continue with next step.

3. Using CAIMS, check for probes stable capacitance values. Move the FMQGC box and harness.

   1. If capacitance values are good, suspect an intermittent fault and go to step 5.
   2. If capacitance values are out of range or unstable (small variation is acceptable), continue with next step.

4. Re-rack the FMQGC, ensuring it is completely engaged with connector A47BP1.

   1. If system checks are good, do close out.
   2. If fault remains, continue with next step.

5. Using CAIMS, LRU Test Page, check for probes stable capacitance values. Ensure no intermittent connection of the excitation line wiring and connectors (A47BP1, CJ412, CP412 and RTP2).

   1. If capacitance values are out of range or unstable (small variation is acceptable), go to step 7.
   2. If capacitance values are good, suspect an intermittent fault and continue with next step.

6. Using the alternate method, check for excitation line connectors (A47BP1, CJ412, CP412 and RTP2), using a digital AC Voltmeter. Measure the excitation voltage between the center pin and the connector body at connector RTP2.

   1. If voltage is 5.3 VAC (approx.) and stable, suspect it is an intermittent fault. Repair as required and do close out.
   2. If voltage is 3.2 VAC (approx.), it is a wiring fault. Repair as required and do close out.

7. Perform continuity check for shield termination between connector RTP2 and A47BP1.

   1. If there is no continuity, repair defective wiring as required and do close out.
   2. If there is continuity, continue with next step.

8. Check FMQGC connectors A47BP1 and A47BJ1 for security and proper assembly (repair as required).

   • Ensure center pin 5 is not recessed, the pin is crimped properly and secured to shield pin 5S
   • Ensure shield pin 5S is crimped properly and locked to connector A47BP1
   • Ensure center contact socket/pin has good friction and they are not bent

   1. If system checks are good, do close out.
   2. If fault remains, continue with next step.

9. Check connector CJ412, CP412 and RTP2 for security and proper assembly (repair as required).
   NOTE: It will be easier to use a Megger meter at this point as access to CJ412 connector will require floor board removal. Ensure all connectors are disconnected, the fuel tank external connector is disconnected (do not allow high voltage inside the fuel tank), and ensure the FMQGC is removed from the rack. If a problem is found, closer access will be required for the repair.

   • Observe all safety precautions called out in SPM 20-00-01-02 and SPM 20-12-01-05
   • Do not use Megger if flammable fumes are present
   • Shield cable nut (jam nut) is secured
   • Center pin is corrosion free and soldered properly to the cable
   • Proper cable shield termination to connector

   1. If system checks are good, do close out.
   2. If fault remains, continue with next step.

10. With the FMQGC removed, check for open circuit between the center conductor and the shield at connector RTP2. The resistance value should be very high (>100 Mega Ohms range) and stable (repair as required).

    • If system checks are good, do close out.
    • If fault remains (suspect an intermittent fault inside the tank), continue with next step.

11. Defuel the aircraft and drain the tanks. Check for water droplets or biological growth on access cover, probe and in surrounding area. Access connector RTJ2 and probe TU6R (If water contamination is found, clean tank and ventilate to dry it out, remove probe and clean in alcohol bath before re-installation).

    1. If system checks are good, do close out.
    2. If fault remains, continue with next step.
       NOTE: If there is access to a known serviceable FMQGC, now is the time to swap FMQGCs for troubleshooting.

12. Check security of terminals for excitation line wiring and connector between RTJ2 and TU6R (repair as required):

    • Ensure shield termination is crimped properly and secured to probe clamping
    • Ensure conductor lugs are properly torque on probe terminals
    • Ensure terminals are corrosion free
    • Measure Excitation Voltage at Probe, 5.3 VAC (approx)

    1. If system checks are good, do close out.
    2. If fault remains, go to step 16.

13. Using CAIMS, LRU Test Page, check probe TU6R capacitance value:

    1. If capacitance value is good, go to step 15.
    2. If capacitance value is out of range or unstable (small variation is acceptable), continue with next step.
       NOTE: As a quick reference, compare TU6L and TU6R for capacitance values if left and right tanks have the same quantity of fuel.

14. Check probe TU6R for contamination (clean probe if contaminated).

    1. If system checks are good, do close out.
    2. If fault remains, continue with next step.

15. Perform wiring checks between TU6R probe and FMQGC.
    NOTE: No wire splicing or insulation repair allowed inside the fuel tanks.

    1. If wiring checks are not good, repair defective wiring as required and do close out.
    2. If wiring checks are good, continue with next step.

16. Replace probe unit TU6R.

    1. If system checks are good, do close out.
    2. If fault remains, continue with next step.

17. Reset FMQGC power in a last chance to clear the fault.

    1. If system checks are good, do close out.
    2. If fault remains, continue with next step.

18. Replace the FMQGC.
19. Do close out.