C9.3 Marine Auxiliary and Generator Set Engine Caterpillar

Table 1 lists the diagnostic trouble codes that apply to the engines that are covered in this manual. Use the Caterpillar Electronic Technician (ET) in order to determine the codes that are active or logged. Then refer to the appropriate troubleshooting procedure for more information.

Further explanations of diagnostic codes are explained after Table 1.

Portions of this material are reprinted with permission from SAE J1939DA_201607^© 2016 SAE International. SAE International is not responsible for any use or translation of this material, in whole or in part. Contact SAE International to obtain a complete copy of SAE J1939DA_201607, the official definitive source of this standard.

Note: A requirement for all troubleshooting is that the troubleshooting is based on active and/or passive diagnostic trouble codes. Do not troubleshoot based on flash codes alone.

Table 1

Cross-Reference from Diagnostic Trouble Codes to Functional Test or Procedure
J1939 Code and Description	Troubleshooting Procedure	Flash Codes
28-3 Accelerator Pedal Position #3 : Voltage Above Normal	Troubleshooting, "Speed Control - Test"	N/A
28-4 Accelerator Pedal Position #3 : Voltage Below Normal	Troubleshooting, "Speed Control - Test"	N/A
29-3 Accelerator Pedal Position 2 : Voltage Above Normal	Troubleshooting, "Speed Control - Test"	N/A
29-4 Accelerator Pedal Position 2 : Voltage Below Normal	Troubleshooting, "Speed Control - Test"	N/A
29-8 Accelerator Pedal Position 2 : Abnormal Frequency, Pulse Width, or Period	Troubleshooting, "Speed Control - Test"	N/A
91-3 Accelerator Pedal Position 1 : Voltage Above Normal	Troubleshooting, "Speed Control - Test"	N/A
91-4 Accelerator Pedal Position 1 : Voltage Below Normal	Troubleshooting, "Speed Control - Test"	N/A
91-8 Accelerator Pedal Position 1 : Abnormal Frequency, Pulse Width, or Period	Troubleshooting, "Speed Control - Test"	N/A
94-16 Engine Fuel Delivery Pressure : High - moderate severity (2)	Troubleshooting, "Fuel Pressure Is High"	N/A
96-3 Fuel Level : Voltage Above Normal	Troubleshooting, "Fuel Level - Test"	N/A
96-4 Fuel Level : Voltage Below Normal	Troubleshooting, "Fuel Level - Test"	N/A
96-17 Fuel Level : Low - least severe (1)	Add fuel to the fuel tank. Refer to the literature that is provided by the OEM of the vessel for the correct procedure.	N/A
98-1 Engine Oil Level : Low - most severe (3)	Troubleshooting, "Oil Level Is Low"	N/A
98-17 Engine Oil Level : Low - least severe (1)	Troubleshooting, "Oil Level Is Low"	N/A
98-18 Engine Oil Level : Low - moderate severity (2)	Troubleshooting, "Oil Level Is Low"	N/A
100-1 Engine Oil Pressure : Low - most severe (3)	Troubleshooting, "Oil Pressure Is Low"	N/A
100-3 Engine Oil Pressure : Voltage Above Normal	Troubleshooting, "Sensor Signal (Analog, Active) - Test"	N/A
100-4 Engine Oil Pressure : Voltage Below Normal	Troubleshooting, "Sensor Signal (Analog, Active) - Test"	N/A
100-17 Engine Oil Pressure : Low - least severe (1)	Troubleshooting, "Oil Pressure Is Low"	N/A
100-18 Engine Oil Pressure : Low - moderate severity (2)	Troubleshooting, "Oil Pressure Is Low"	N/A
101-3 Engine Crankcase Pressure : Voltage Above Normal	Troubleshooting, "Sensor Signal (Analog, Active) - Test"	N/A
101-4 Engine Crankcase Pressure : Voltage Below Normal	Troubleshooting, "Sensor Signal (Analog, Active) - Test"	N/A
101-13 Engine Crankcase Pressure : Calibration Required	Troubleshooting, "Sensor Calibration Required - Test"	N/A
102-18 Engine Intake Manifold #1 Pressure : Low - moderate severity (2)	Troubleshooting, "Intake Manifold Air Pressure Is Low"	N/A
105-0 Engine Intake Manifold #1 Temperature : High - most severe (3)	Troubleshooting, "Intake Manifold Air Temperature Is High"	N/A
105-3 Engine Intake Manifold #1 Temperature : Voltage Above Normal	Troubleshooting, "Sensor Signal (Analog, Active) - Test"	N/A
105-4 Engine Intake Manifold #1 Temperature : Voltage Below Normal	Troubleshooting, "Sensor Signal (Analog, Active) - Test"	N/A
105-15 Engine Intake Manifold #1 Temperature : High - least severe (1)	Troubleshooting, "Intake Manifold Air Temperature Is High"	N/A
105-16 Engine Intake Manifold #1 Temperature : High - moderate severity (2)	Troubleshooting, "Intake Manifold Air Temperature Is High"	N/A
109-1 Engine Coolant Pressure : Data Low - Most Severe (3)	Troubleshooting, "Coolant Pressure Is Low"	N/A
109-3 Engine Coolant Pressure : Voltage Above Normal	Troubleshooting, "Sensor Signal (Analog, Active) - Test"	N/A
109-4 Engine Coolant Pressure : Voltage Below Normal	Troubleshooting, "Sensor Signal (Analog, Active) - Test"	N/A
109-17 Engine Coolant Pressure : Low - least severe (1)	Troubleshooting, "Coolant Pressure Is Low"	N/A
109-18 Engine Coolant Pressure : Low - moderate severity (2)	Troubleshooting, "Coolant Pressure Is Low"	N/A
110-0 Engine Coolant Temperature : High - most severe (3)	Troubleshooting, "Coolant Temperature is High"	N/A
110-3 Engine Coolant Temperature : Voltage Above Normal	Troubleshooting, "Sensor Signal (Analog, Passive) - Test"	133
110-4 Engine Coolant Temperature : Voltage Below Normal	Troubleshooting, "Sensor Signal (Analog, Passive) - Test"	133
110-15 Engine Coolant Temperature : High - least severe (1)	Troubleshooting, "Coolant Temperature is High"	N/A
110-16 Engine Coolant Temperature : High - moderate severity (2)	Troubleshooting, "Coolant Temperature is High"	N/A
110-17 Engine Coolant Temperature : Low - least severe (1)	Troubleshooting, "Coolant Temperature is Low"	N/A
111-1 Engine Coolant Level : Low - most severe (3)	Troubleshooting, "Coolant Level Is Low"	N/A
111-17 Engine Coolant Level : Low - least severe (1)	Troubleshooting, "Coolant Level Is Low"	N/A
111-18 Engine Coolant Level : Low - moderate severity (2)	Troubleshooting, "Coolant Level Is Low"	N/A
157-3 Engine Injector Metering Rail #1 Pressure : Voltage Above Normal	Troubleshooting, "Sensor Signal (Analog, Active) - Test"	133
157-4 Engine Injector Metering Rail #1 Pressure : Voltage Below Normal	Troubleshooting, "Sensor Signal (Analog, Active) - Test"	133
157-17 Engine Injector Metering Rail #1 Pressure : Low - least severe (1)	Troubleshooting, "Fuel Rail Pressure Is Low"	N/A
168-3 Battery Potential / Power Input 1 : Voltage Above Normal	Troubleshooting, "Electrical Power Supply - Test"	422
168-4 Battery Potential / Power Input 1 : Voltage Below Normal	Troubleshooting, "Electrical Power Supply - Test"	422
172-3 Engine Air Inlet Temperature : Voltage Above Normal	Troubleshooting, "Sensor Signal (Analog, Passive) - Test"	133
172-4 Engine Air Inlet Temperature : Voltage Below Normal	Troubleshooting, "Sensor Signal (Analog, Passive) - Test"	133
173-0 Engine Exhaust Gas Temperature : High - most severe (3)	Troubleshooting, "Exhaust Temperature is High"	N/A
173-3 Engine Exhaust Gas Temperature : Voltage Above Normal	Troubleshooting, "Sensor Signal (Analog, Passive) - Test"	N/A
173-4 Engine Exhaust Gas Temperature : Voltage Below Normal	Troubleshooting, "Sensor Signal (Analog, Passive) - Test"	N/A
173-8 Engine Exhaust Gas Temperature : Abnormal Frequency, Pulse Width, or Period	Troubleshooting, "Sensor Signal (Analog, Passive) - Test"	N/A
173-15 Engine Exhaust Gas Temperature : High - least severe (1)	Troubleshooting, "Exhaust Temperature is High"	N/A
173-16 Engine Exhaust Gas Temperature : High - moderate severity (2)	Troubleshooting, "Exhaust Temperature is High"	N/A
174-0 Engine Fuel Temperature 1 : High - most severe (3)	Troubleshooting, "Fuel Temperature is High"	N/A
174-3 Engine Fuel Temperature 1 : Voltage Above Normal	Troubleshooting, "Sensor Signal (Analog, Passive) - Test"	165
174-4 Engine Fuel Temperature 1 : Voltage Below Normal	Troubleshooting, "Sensor Signal (Analog, Passive) - Test"	165
174-15 Engine Fuel Temperature 1 : High - least severe (1)	Troubleshooting, "Fuel Temperature is High"	N/A
174-16 Engine Fuel Temperature 1 : High - moderate severity (2)	Troubleshooting, "Fuel Temperature is High"	N/A
175-0 Engine Oil Temperature 1 : High - most severe (3)	Troubleshooting, "Engine Oil Temperature is High"	N/A
175-3 Engine Oil Temperature 1 : Voltage Above Normal	Troubleshooting, "Sensor Signal (Analog, Passive) - Test"	N/A
175-4 Engine Oil Temperature 1 : Voltage Below Normal	Troubleshooting, "Sensor Signal (Analog, Passive) - Test"	N/A
175-15 Engine Oil Temperature 1 : High - least severe (1)	Troubleshooting, "Engine Oil Temperature is High"	N/A
175-16 Engine Oil Temperature 1 : High - moderate severity (2)	Troubleshooting, "Engine Oil Temperature is High"	N/A
190-0 Engine Speed : High - most severe (3)	Troubleshooting, "Engine Overspeeds"	N/A
190-8 Engine Speed : Abnormal Frequency, Pulse Width, or Period	Troubleshooting, "Speed/Timing - Test"	141
190-15 Engine Speed : High - least severe (1)	Troubleshooting, "Engine Overspeeds"	N/A
411-3 Engine Exhaust Gas Recirculation Differential Pressure : Voltage Above Normal	Troubleshooting, "Sensor Signal (Analog, Active) - Test"	N/A
441-0 Auxiliary Temperature #1 : High - most severe (3)	Troubleshooting, "Symptom Troubleshooting" The troubleshooting procedure will depend on the symptoms.	N/A
441-3 Auxiliary Temperature #1 : Voltage Above Normal	Troubleshooting, "Symptom Troubleshooting" The troubleshooting procedure will depend on the symptoms.	N/A
441-4 Auxiliary Temperature #1 : Voltage Below Normal	Troubleshooting, "Symptom Troubleshooting" The troubleshooting procedure will depend on the symptoms.	N/A
441-15 Auxiliary Temperature #1 : High - least severe (1)	Troubleshooting, "Symptom Troubleshooting" The troubleshooting procedure will depend on the symptoms.	N/A
441-16 Auxiliary Temperature #1 : High - moderate severity (2)	Troubleshooting, "Symptom Troubleshooting" The troubleshooting procedure will depend on the symptoms.	N/A
630-2 Calibration Memory : Erratic, Intermittent, or Incorrect	Troubleshooting, "Configuration Parameters"	527
631-2 Calibration Module : Erratic, Intermittent, or Incorrect	Troubleshooting, "ECM Software - Install"	N/A
637-11 Engine Timing Sensor : Other Failure Mode	Troubleshooting, "Timing - Calibrate"	143
637-13 Engine Timing Sensor : Calibration Required	Troubleshooting, "Timing - Calibrate"	143
639-9 J1939 Network #1 : Abnormal Update Rate	Troubleshooting, "Data Link - Test"	N/A
639-14 J1939 Network #1 : Special Instruction	Troubleshooting, "Data Link - Test"	N/A
651-2 Engine Injector Cylinder #01 : Erratic, Intermittent, or Incorrect	Troubleshooting, "Injector Solenoid - Test"	111/139
651-5 Engine Injector Cylinder #01 : Current Below Normal	Troubleshooting, "Injector Solenoid - Test"	111/139
651-6 Engine Injector Cylinder #01 : Current Above Normal	Troubleshooting, "Injector Solenoid - Test"	111/139
651-7 Engine Injector Cylinder #01 : Not Responding Properly	Troubleshooting, "Injector Solenoid - Test"	111/139
652-2 Engine Injector Cylinder #02 : Erratic, Intermittent, or Incorrect	Troubleshooting, "Injector Solenoid - Test"	112/139
652-5 Engine Injector Cylinder #02 : Current Below Normal	Troubleshooting, "Injector Solenoid - Test"	112/139
652-6 Engine Injector Cylinder #02 : Current Above Normal	Troubleshooting, "Injector Solenoid - Test"	112/139
652-7 Engine Injector Cylinder #02 : Not Responding Properly	Troubleshooting, "Injector Solenoid - Test"	112/139
653-2 Engine Injector Cylinder #03 : Erratic, Intermittent, or Incorrect	Troubleshooting, "Injector Solenoid - Test"	113/139
653-5 Engine Injector Cylinder #03 : Current Below Normal	Troubleshooting, "Injector Solenoid - Test"	113/139
653-6 Engine Injector Cylinder #03 : Current Above Normal	Troubleshooting, "Injector Solenoid - Test"	113/139
653-7 Engine Injector Cylinder #03 : Not Responding Properly	Troubleshooting, "Injector Solenoid - Test"	113/139
654-2 Engine Injector Cylinder #04 : Erratic, Intermittent, or Incorrect	Troubleshooting, "Injector Solenoid - Test"	114/139
654-5 Engine Injector Cylinder #04 : Current Below Normal	Troubleshooting, "Injector Solenoid - Test"	114/139
654-6 Engine Injector Cylinder #04 : Current Above Normal	Troubleshooting, "Injector Solenoid - Test"	114/139
654-7 Engine Injector Cylinder #04 : Not Responding Properly	Troubleshooting, "Injector Solenoid - Test"	114/139
655-2 Engine Injector Cylinder #05 : Erratic, Intermittent, or Incorrect	Troubleshooting, "Injector Solenoid - Test"	115/139
655-5 Engine Injector Cylinder #05 : Current Below Normal	Troubleshooting, "Injector Solenoid - Test"	115/139
655-6 Engine Injector Cylinder #05 : Current Above Normal	Troubleshooting, "Injector Solenoid - Test"	115/139
655-7 Engine Injector Cylinder #05 : Not Responding Properly	Troubleshooting, "Injector Solenoid - Test"	115/139
656-2 Engine Injector Cylinder #06 : Erratic, Intermittent, or Incorrect	Troubleshooting, "Injector Solenoid - Test"	116/139
656-5 Engine Injector Cylinder #06 : Current Below Normal	Troubleshooting, "Injector Solenoid - Test"	116/139
656-6 Engine Injector Cylinder #06 : Current Above Normal	Troubleshooting, "Injector Solenoid - Test"	116/139
656-7 Engine Injector Cylinder #06 : Not Responding Properly	Troubleshooting, "Injector Solenoid - Test"	116/139
677-5 Engine Starter Motor Relay : Current Below Normal	Troubleshooting, "Relay - Test"	N/A
677-6 Engine Starter Motor Relay : Current Above Normal	Troubleshooting, "Relay - Test"	N/A
678-3 ECU 8 Volts DC Supply : Voltage Above Normal	Troubleshooting, "Sensor Supply - Test"	N/A
678-4 ECU 8 Volts DC Supply : Voltage Below Normal	Troubleshooting, "Sensor Supply - Test"	N/A
723-8 Engine Speed Sensor #2 : Abnormal Frequency, Pulse Width, or Period	Troubleshooting, "Speed/Timing - Test"	N/A
931–5 Engine Fuel Supply Pump Actuator: Current Below Normal	Troubleshooting, "Fuel Priming Pump- Test"	N/A
931–6 Engine Fuel Supply Pump Actuator: Current Above Normal	Troubleshooting, "Fuel Priming Pump- Test"	N/A
971-31 Engine Derate Switch	The monitoring system override switch has been activated. Engine derates are prevented when this event is active.	N/A
974-5 Remote Accelerator Pedal Position : Current Below Normal	Troubleshooting, "Speed Control - Test"	N/A
974-6 Remote Accelerator Pedal Position : Current Above Normal	Troubleshooting, "Speed Control- Test"	N/A
1208-3 Engine Pre-filter Oil Pressure : Voltage Above Normal	Troubleshooting, "Sensor Signal (Analog, Active) - Test"	N/A
1208-4 Engine Pre-filter Oil Pressure : Voltage Below Normal	Troubleshooting, "Sensor Signal (Analog, Active) - Test"	N/A
1237-31 Engine Shutdown Override Switch	The Engine Shutdown Override Switch is used to keep the engine running when the ECM is commanding that the engine be shutdown for reasons other than inducement-related events. If this code is present, there may be damage to the engine. This code indicates that the operator chose to keep the engine running in conditions that typically can damage the engine.	N/A
1239-0 Engine Fuel Leakage 1 : High - most severe (3)	Troubleshooting, "Fuel Rail Pressure Leakage Is High"	N/A
1239-31 Engine Fuel Leakage 1	Troubleshooting, "Fuel Rail Pressure Leakage Is High"	N/A
1347-5 Engine Fuel Pump Pressurizing Assembly #1 : Current Below Normal	Troubleshooting, "Fuel Injection Pump - Test"	N/A
1347-6 Engine Fuel Pump Pressurizing Assembly #1 : Current Above Normal	Troubleshooting, "Fuel Injection Pump - Test"	N/A
1348-5 Engine Fuel Pump Pressurizing Assembly #2 : Current Below Normal	Troubleshooting, "Fuel Injection Pump - Test"	N/A
1348-6 Engine Fuel Pump Pressurizing Assembly #2 : Current Above Normal	Troubleshooting, "Fuel Injection Pump - Test"	N/A
1381-3 Engine Fuel Supply Pump Inlet Pressure : Voltage Above Normal	Troubleshooting, "Sensor Signal (Analog, Active) - Test"	N/A
1381-4 Engine Fuel Supply Pump Inlet Pressure : Voltage Below Normal	Troubleshooting, "Sensor Signal (Analog, Active) - Test"	N/A
1387-0 Auxiliary Pressure #1 : High - most severe (3)	Troubleshooting, "Symptom Troubleshooting" The troubleshooting procedure will depend on the symptoms.	N/A
1387-3 Auxiliary Pressure #1 : Voltage Above Normal	Troubleshooting, "Symptom Troubleshooting" The troubleshooting procedure will depend on the symptoms.	N/A
1387-4 Auxiliary Pressure #1 : Voltage Below Normal	Troubleshooting, "Symptom Troubleshooting" The troubleshooting procedure will depend on the symptoms.	N/A
1387-15 Auxiliary Pressure #1 : High - least severe (1)	Troubleshooting, "Symptom Troubleshooting" The troubleshooting procedure will depend on the symptoms.	N/A
1387-16 Auxiliary Pressure #1 : High - moderate severity (2)	Troubleshooting, "Symptom Troubleshooting" The troubleshooting procedure will depend on the symptoms.	N/A
1656-2 Engine Automatic Start Enable Switch : Erratic, Intermittent, or Incorrect	Troubleshooting, "Engine Control Switch - Test"	N/A
1664-31 Engine Automatic Start Failed	Troubleshooting, "Engine Overcrank Occurrence"	N/A
2435-3 Seawater Pump Outlet Pressure : Voltage Above Normal	Troubleshooting, "Sensor Signal (Analog, Active) - Test"	N/A
2435-4 Seawater Pump Outlet Pressure : Voltage Below Normal	Troubleshooting, "Sensor Signal (Analog, Active) - Test"	N/A
2435-17 Seawater Pump Outlet Pressure : Low - least severe (1)	Troubleshooting, "Sea Water Pump Pressure Problem"	N/A
2630-1 Engine Charge Air Cooler Outlet Temperature : Voltage Above Normal	Troubleshooting, "Sensor Signal (Analog, Passive) - Test"	N/A
2648-5 Maintenance Lamp : Current Below Normal	N/A	N/A
2648-6 Maintenance Lamp : Current Above Normal	N/A	N/A
3509-3 Sensor Supply Voltage 1 : Voltage Above Normal	Troubleshooting, "Sensor Supply - Test"	516
3509-4 Sensor Supply Voltage 1 : Voltage Below Normal	Troubleshooting, "Sensor Supply - Test"	516
3510-3 Sensor Supply Voltage 2 : Voltage Above Normal	Troubleshooting, "Sensor Supply - Test"	516
3510-4 Sensor Supply Voltage 2 : Voltage Below Normal	Troubleshooting, "Sensor Supply - Test"	516
3563-3 Engine Intake Manifold #1 Absolute Pressure : Voltage Above Normal	Troubleshooting, "Sensor Signal (Analog, Active) - Test"	197
3563-4 Engine Intake Manifold #1 Absolute Pressure : Voltage Below Normal	Troubleshooting, "Sensor Signal (Analog, Active) - Test"	197
3563-13 Engine Intake Manifold #1 Absolute Pressure : Calibration Required	Troubleshooting, "Sensor Calibration Required - Test"	197
3563-21 Engine Intake Manifold #1 Absolute Pressure : Data Drifted Low	Troubleshooting, "Sensor Supply - Test"	N/A
5578-3 Engine Fuel Delivery Absolute Pressure : Voltage Above Normal	Troubleshooting, "Sensor Signal (Analog, Active) - Test"	N/A
5578-4 Engine Fuel Delivery Absolute Pressure : Voltage Below Normal	Troubleshooting, "Sensor Signal (Analog, Active) - Test"	N/A
5578-21 Engine Fuel Delivery Absolute Pressure : Data Drifted Low	Troubleshooting, "Sensor Supply - Test"	N/A
5580-3 Engine Filtered Fuel Delivery Absolute Pressure : Voltage Above Normal	Troubleshooting, "Sensor Signal (Analog, Active) - Test"	N/A
5580-4 Engine Filtered Fuel Delivery Absolute Pressure : Voltage Below Normal	Troubleshooting, "Sensor Signal (Analog, Active) - Test"	N/A
5580-17 Engine Filtered Fuel Delivery Absolute Pressure : Low - least severe (1)	Troubleshooting, "Fuel Pressure Is Low"	N/A
5580-21 Engine Filtered Fuel Delivery Absolute Pressure : Data Drifted Low	Troubleshooting, "Sensor Supply - Test"	N/A
5584-15 Engine Fuel Filter Degradation : High - least severe (1)	Troubleshooting, "Fuel Filter Is Restricted"	N/A
5584-16 Engine Fuel Filter Degradation : High - moderate severity (2)	Troubleshooting, "Fuel Filter Is Restricted"	N/A
5585-17 Engine Injector Metering Rail #1 Cranking Pressure : Low - least severe (1)	Troubleshooting, "Fuel Rail Pressure Is Low While Cranking"	N/A
7471-15 Engine Oil Filter Differential Pressure : High - least severe (1)	Troubleshooting, "Oil Filter Differential Pressure Problem"	N/A

Diagnostic Codes

Diagnostic codes alert the operator that a problem in the electronic system has been detected. Diagnostic codes are also used by the service technician to identify the nature of the problem. Cat^® Electronic Technician (ET) is a software program that runs on a personal computer. The software can be used by the service technician to view the diagnostic code information for an ECM. The diagnostic code will be displayed as a two-element code. The following terms describe the elements of the code:

Suspect Parameter Number (SPN) - The SPN is a code which is assigned to each component to identify data.

Failure Mode Identifier (FMI) - The FMI indicates the type of failure.

Refer to Table 1 for a complete list of the diagnostic codes and the appropriate troubleshooting procedure.

Note: Do not confuse diagnostic codes with event codes. Event codes alert the operator that an abnormal operating condition such as low oil pressure or high coolant temperature has been detected. If an event code is active, refer to Troubleshooting, "Event Codes".

Illustration 1 is an example of the operating range of a sensor.

Illustration 1	g01365757
Example of the typical operating range of a sensor (1) This area represents the normal operating range of the engine parameter. (2) In these areas, the engine is operating in an unsafe operating range of the monitored parameter. An event code will be generated for the monitored parameter. The sensor circuit does not have an electronic problem. Refer to Troubleshooting, "Event Codes" for additional information on event codes. (3) In these areas, the signal from the sensor is outside of the operating range of the sensor. The sensor circuit has an electronic problem. A diagnostic code will be generated for the sensor circuit.

Active Diagnostic Codes

An active diagnostic code represents a problem with the electronic control system. Correct the problem as soon as possible.

When the ECM generates an active diagnostic code. The "Active Alarm" indicator ("Control Alarm Status" on Cat ET) is activated to alert the operator. If the condition that generated the code is momentary, the message disappears from the list of active diagnostic codes. The diagnostic code becomes logged.

Logged Diagnostic Codes

When the ECM generates a diagnostic code, the ECM logs the code in permanent memory. The ECM has an internal diagnostic clock. Each ECM will record the following information when a code is generated:

• The hour of the first occurrence of the code

• The hour of the last occurrence of the code

• The number of occurrences of the code

This information is a valuable indicator for troubleshooting intermittent problems.

A code is cleared from memory when one of the following conditions occur:

• The service technician manually clears the code.

• The code does not recur for 100 hours.

• A new code is logged and there are already ten codes in memory. In this case, the oldest code is cleared.

Some diagnostic codes may be easily triggered. Some diagnostic codes may log occurrences that did not result in complaints. The most likely cause of an intermittent problem is a faulty connection or damaged wiring. The next likely cause is a component failure. The least likely cause is the failure of an electronic module. Diagnostic codes that are logged repeatedly may indicate a problem that needs special investigation.

Note: Always clear logged diagnostic codes after investigating and correcting the problem which generated the code.