Cummins ISB CM550 (1990-94) Fault Code: 381 PID: SID 237 SPN: 626 FMI: 11 Intake Air Heater Relay Circuit

Circuit Description
The intake air heater improves starting and white smoke control in cold ambient conditions.
The ECM controls relays that switch power to the air heater. There are two heating coils in the heater that are individually controlled by the ECM.

Component Location
The intake air heater is located at the air inlet connection into the intake manifold. The location of the heater relays will vary with the OEM.

Shop Talk
1) These faults could also indicate the intake air heater circuits are shorted to battery (+).
This would command the grids to be on full time. This will drain the batteries, burn out
grids, and/or destroy intake gaskets.
2) The intake air heater circuits will only activate when intake manifold temperature is below