Gillig bus converted- Looking for retarder info

Detroit series 50 engine, Allison transmission. This unit has been modified into a motor home. Retarder does not work, wired to schematics that I could find with a module and joystick type controller as well as on/off switch. Have not been able to get it to activate during road tests. Have two codes Engine speed sensor, (22-14) and oil level (14-12). Not sure if these will have an effect on it activating or not. Also the cooling fan is supposed to be PWM variable speed but runs wide open. I...

Gillig bus converted- Looking for retarder info

Gillig bus converted- Looking for retarder info