Truck Repair: N14 decel, coolant level, crank sensor

Question
N14 435 in 1998 navistar quad dump236000 miles. Engine light comes on and rpms are limited to 1400-1500, sometimes for a second, sometimes up to 10 minutes.This can happen on and off all day long, and it can go 2 weeks without happening.Engine light doesnt always come on or correspond with deceleration. Service shop had it 3 times in last year and a half, first replaced an injector, next time replaced wiring harness,tps was changed, crank sensor was changed. next they say they will have to replace ecm!$$$ Trouble code 235 flashes. Thanks, MIKE

Answer
Fault 235 is low coolant level.Either the sensor is bad or the wiring(OEM) harness from low coolant level sensor to ecm harness is bad.I would also check the tail yoke on transmission to see if nut is tight.That would cause a 1400-1500 RPM derate for a parameter is set in ECM(max speed w/o vss).You could ask them(or tell them)to by-pass the sensor & try it before you ever think about that $2500 ECM.