Check FHR Circuit
electrical
Description
A problem was detected in the fuel heater relay coil circuit, shorted while operating or open when not operating, and the unit gives alarm only.
Activation Conditions
A problem has been detected in the fuel heater relay coil circuit. If this alarm occurs while the fuel heater circuit is operating, the circuit is detected shorted. If this alarm occurs while the fuel heater circuit is not operating, the circuit is detected open.
Unit Behavior
Alarm only.
Reset Conditions
Auto reset when the circuit is normal, or Alarm may be manually reset using the display mounted keys or by turning the unit off, then back on again.
Corrective Actions
1. Check Relay a. Inspect relay socket and connection pins inside PCM. No damage to relay. No damaged or corroded connections. b. Check resistance of coil (terminals 85 and 86). Refer to Section 1.11 for specifications. 2. Check Power and Wiring a. Check for power at fuse F10 terminal A inside PCM. Minimum 11 VDC. If not, check PER circuit and fuse F5. (NOTE: FLS, SATPWR and LB will also be without power.) b. Check fuses F5 and F10. Verify correct fuse, see Figure 1.7. c. Check for power at FHR + terminal. Replace PCM. d. If the ambient temperature is below 77°F (25°C) the fuel heater relay (FHR) will be grounded by the main microprocessor at 3MM-17. Power up control system in PC mode. (Refer to Section 1.3.2). Check ground from 3MM-17 through PCM-17 to the FHR - connection. If ambient is above 77°F (25°C), place the SROS in the OFF position and check continuity of the wiring from 3MM-17 through PCM-17 to the FHR - connection. Good ground. If not, check connectors and wiring between terminals. Verify no damage, moisture or corrosion. e. Check resistance of heater element. Refer to Section 1.11 for specifications.