TUBE AS 2591971 - Caterpillar

Table 1
Diagnostic Trouble Codes
Code Description Conditions Present Response
676-0 Glow Plug Heater Relay Driving Circuit Overheat Overheat of glow plug driving circuit.
Battery voltage is normal.
Glow relay is being energized.
Glow relay coil resistance or load is too high that the specified value of ECU for 3 seconds or more.
Hard starting and white smoke at low temperature. None
676-5 Open Circuit of GLow Plug Relay Driving Circuit Battery voltage is normal.
Glow relay is energized.
Open circuit of harness or relay coil for 3 seconds or more.
Hard starting and white smoke in cold temperatures. None
523544-3 +B Short of Glow Plug Relay Driving Circuit +B short of glow relay driving circuit
Battery voltage is normal
Glow relay is being energized.
+B short circuit of harness for 3 seconds or more.
Hard starting and white smoke at low temperature. Warning Level 2
523544-4 Ground Short of Glow Plug Relay Driving Circuit Ground short of glow relay driving circuit
Battery voltage is normal
Glow relay is being energized.
Ground short circuit of harness for 3 seconds or more.
Hard starting and white smoke at low temperature. None When the conditions are met for the glow plugs to active, the Engine ECM provides the power to the relay from E1-35 and 12 volts from V2-50.The Engine EC activates the glow plug relay by providing 12 volts from E1-35 and the ground from V2-50 as shown in the previous graphic. These codes are showing either a glow plug relay issue or a harness issue between the Engine ECM and the glow plug relay.Note: To help in troubleshooting, a dummy resistor of 15 to 25 ohms can be installed across the coolant temperature switch connector to make the engine ECM believe that coolant temperature is below 50 °F. This will activate the glow plug relay with Key Switch ON.
Illustration 1 g06113075
(1) Terminal +B
(2) Terminal glow plug
(3) Terminal glow relay (+)
(4) Terminal ground
(a) Fuse
(b) Glow relay
(c) ECU connector
(d) ECU connector 2
(A) To glow plug
Table 2
Troubleshooting Test Steps Values Results
1. Check for Bent ECM Pins and Damaged Connector Sockets
ECM Pins and Connector
Result: The ECM pins are bent or EC connector is damaged.
Replace the ECM or engine harness.
Result: There is no issue found.
Proceed to Test Step 2.
2. Inspect Electrical Connectors and Wiring
A. Check the harness from the engine ECM to the glow plug relay. Check the harness for corrosion, abrasion, pinch points, or any damage.
B. There will be at least one connector that these will route through as the wires go from the engine harness to the machine harness. Check the connector's pins and sockets are not damaged, are aligned, and fully seated.
- Check for continuity at the plug back to the Engine ECM.
- Check for continuity at the plug to the glow plug relay.
Refer to the machine schematic.
Loose connections, poor routings, damaged wires
Result: There is a fault in a connector or wiring.
Replace the engine harness.
Result: There is no fault found in the harness.
Proceed to Test Step 3.
3. Check the Glow Plug Relay
A. Check the resistance of the glow plug relay (refer to the machine service manual for the specification).
B. When the glow