B737 captain reported a rejected takeoff caused by engine 1 not making required power.

Attributes
ACN	1701609
Time
Date	201911
Local Time Of Day	1201-1800
Place
Locale Reference	LAS.Airport
State Reference	NV
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Make Model Name	B737 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	Takeoff
Flight Plan	IFR
Component
Aircraft Component	Turbine Engine
Person 1
Function	Captain Pilot Flying
Qualification	Flight Crew Air Transport Pilot (ATP) Flight Crew Instrument Flight Crew Multiengine
Experience	Flight Crew Last 90 Days 169 Flight Crew Total 15400 Flight Crew Type 6440
Events
Anomaly	Aircraft Equipment Problem Critical Deviation - Procedural Published Material / Policy Deviation - Procedural Maintenance

Narrative:

After advancing the thrust levers and verifying symmetric thrust; I engaged the auto throttles and monitored the advancement of thrust to the specified value. Engine 2 thrust increased to the value specified for the takeoff; 102 pct. With thrust levers matched; engine 1 thrust did not increase above 95 pct. I rejected the takeoff at about 50 kts. We cleared the runway; performed the [rejected takeoff] checklist; and returned to the gate. I sent an elb entry describing the discrepancy.based on review of this aircraft's maintenance history; the same or similar thrust discrepancy was squawked on the two previous flights. Before our departure; ZZZ maintenance explained the history; stating that they had successfully run the engine up to about 90 pct N1 but could not test greater thrust on the ramp. They showed me engine data from the preceding takeoff indicating that the low N1 value was accompanied by low fuel flow; egt; and N2 values. They replaced the N1 sensor and released the aircraft for our flight. With this information; it was not a surprise during our takeoff to see engine 1 not developing the thrust specified on the takeoff performance up link.

Original NASA ASRS Text

Title: B737 Captain reported a rejected takeoff caused by engine 1 not making required power.

Narrative: After advancing the thrust levers and verifying symmetric thrust; I engaged the auto throttles and monitored the advancement of thrust to the specified value. Engine 2 thrust increased to the value specified for the takeoff; 102 pct. With thrust levers matched; engine 1 thrust did not increase above 95 pct. I rejected the takeoff at about 50 kts. We cleared the runway; performed the [Rejected Takeoff] checklist; and returned to the gate. I sent an ELB entry describing the discrepancy.Based on review of this aircraft's maintenance history; the same or similar thrust discrepancy was squawked on the two previous flights. Before our departure; ZZZ Maintenance explained the history; stating that they had successfully run the engine up to about 90 pct N1 but could not test greater thrust on the ramp. They showed me engine data from the preceding takeoff indicating that the low N1 value was accompanied by low fuel flow; EGT; and N2 values. They replaced the N1 sensor and released the aircraft for our flight. With this information; it was not a surprise during our takeoff to see Engine 1 not developing the thrust specified on the takeoff performance up link.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.