DTC C1751-51: Compressor Relay Coil Malfunction [08/2015 - 08/2019]: Description

When the "up" side of the height control switch is pressed, a signal is sent from terminal RC of the suspension control ECU to the AIR SUS relay to turn the relay on.

As a result, the current flows to the AIR SUS relay coil, closing the relay contact, and then battery positive voltage is applied to the height control compressor, which causes compressed air to raise the vehicle height.

DTC Code	DTC Detection Condition	Trouble Area
C1751/51	Either condition is met: With the AIR SUS relay inactivated, an open signal of the AIR SUS relay is detected for 1 second or more. With the AIR SUS relay activated, a short signal of the AIR SUS relay is detected 8 times successively.	Harness or connector AIR SUS relay (Suspension control relay) Suspension control ECU

HINT:

Once the suspension control ECU stores DTC C1751/51 in memory, vehicle height control is suspended until a normal signal is input to the suspension control ECU from the AIR SUS relay. However, control is resumed if the engine switch is turned off and then on (IG) again.