Date: 201808
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Light: Daylight
Aircraft: B737-700
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Climb
Airspace: Class A ZZZ
ATC / advisory: Center ZZZ
Aircraft component: Engine Indications
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: First Officer; Pilot Flying
Reporter qualification: Flight Crew Instrument; Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP)
Second reporter function: Pilot Not Flying; Captain
Anomaly: Aircraft Equipment Problem Less Severe; Inflight Event / Encounter Fuel Issue
Detector: Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Provided Assistance; Flight Crew Requested ATC Assistance / Clarification; Flight Crew FLC Overrode Automation; Flight Crew Landed As Precaution; Flight Crew Landed in Emergency Condition; Flight Crew Returned To Departure Airport
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: On departure from ZZZ; passing through FL 230; we saw the following indications almost simultaneously: Master Caution lights with FUEL and ENG illuminated and left and right fuel Filter Bypass lights illuminated on the upper panel. There were also indications of a computer data problem as the aircraft went into CWS Pitch and out of VNAV with DISPLAY SOURCE 2 (amber; in the bottom left of the PFD). The flight director became unreliable to nonexistent and we began to hand fly off of the raw data; cross checking primary and standby instruments with minimal thrust lever movements. After we leveled off; we ran the QRH for Filter Bypass; [notified ATC]; and returned for a precautionary landing at ZZZ which was uneventful; below MGLW (Maximum Gross Landing Weight); with no hot brake concerns. There were no known deviations from QRH; ATC; or Company procedures despite the aircraft malfunction(s).The QRH is very straightforward regarding the dual Filter Bypass light condition; so we [notified ATC] and returned in a safe and expeditious manner. It wasn't until after we were on the ground and able to reflect on everything; that we began to figure that it was likely not a fuel contamination problem; but a DEU (Display Electronics Units) failure of some sort and we began researching possible connections between that and the Filter Bypass lights. There is nothing that we could find in [our electronic guides] or our manuals linking these conditions... which led to a little head-scratching during the event; although it would not have affected our clear decision to land as soon as possible. Looking back; I would have at least tried the other autopilot to see if maybe that would have alleviated some of the task load; but it was just so much simpler at the time to just hand fly and not spend time worrying about the automation. It would be nice to get some follow-up from Maintenance about what they found.


Second narrative: Climbing out of ZZZ to FL 190 we were cleared to maintain FL 230. As we were about to level off; we had a duel fuel filter bypass. We read the QRH; [notified ATC]; and returned to ZZZ. We do not believe we deviated or oversped; and we did follow QRH; ATC and Company procedures to the best of our knowledge. We did initially lose VNAV but still no deviation.


Synopsis: B737 flight crew reported Master Caution illuminating with Fuel and ENG warning lights led to a return to the departure airport.