96 w900 431 code

Did you have the accerator pedel calibrated when you replaced the ECM?

The two codes relate to this problem on the N14.

 

The idle validation switch is used by the electronic control module (ECM) to indicate when the accelerator pedal or lever is released (on-idle) or depressed (off-idle). The switch is adjusted at the factory to switch from on-idle to off-idle at the correct accelerator pedal or lever position.

Voltage detected simultaneously on both the idle validation off-idle and idle signal pins 6 and 9 of the OEM harness connector or no voltage detected at either pin.
Check for 5v at Pin 10 with key on and at the pedal. Check 6 and 9 w/o depressing the pedal and with depressing the pedal at both the ECM and the pedal.

With keyswitch on, with key switch in on position engine off, gradually push accel pedal to floor and release..do this 3 times..this procedure will recalibrate the ecm and accel pedal..if this is not your problem, inspect wires plugged into pedal, make sure they are tight, free of corrosion...same to bulkhead pass through connector..

This code is usually caused by a loose wire connection-an accel pedal that is not calibrated, or an idle validation switch that is not wired correctly,

Pin 10 on ecm oem harness connector will be your 5 volt supply to sensor, pin 6 is your idle signal back to ecm, pin 9 will be your off idle signal.

Jakes quit working. May have blown a fuse.
FAULT CODE 431 (ISS) - Diesel Engine Troubleshooting (dieselmotors.info)