TM 9-2320-361-34 17-5. ENGINE COOLANT HEATER COMPONENT BRACKET MAINTENANCE (Contd) 1. Check diode (23) for continuity. Reverse leads on diode (23) and check for continuity. If circuit is open in both test conditions or closed in both test conditions, replace diode (23). 2. Check resistor (18) for continuity. If continuity does not exist, replace resistor (18). 17-11