C7 Urban Transit Bus Engines Caterpillar

The exhaust back pressure is monitored by the diagnostic module that monitors back pressure. The module is programmed with software that can not be changed except by the manufacturer. The inlet side of the DPF contains a test port. The test port is used for continuous monitoring of the exhaust back pressure. The test port also sends information about the amount of back pressure in the DPF to the warning lamps that are located on top of the diagnostic module and/or to warning lights on the dash panel. The diagnostic module is located in the engine compartment.

Illustration 1	g01216881
(1) System Status (2) Over Pressure Indicator (3) "Over Temperature Indicator" (4) System Problem Indicator (35) Alarm Reset Indicator

The four operational lights on the diagnostic module must be monitored daily.

Note: Any alarm events must be investigated immediately. Failure to resolve the problem may result in severe damage to the monitor or the engine.

1. The "System Status" light is green when the light is illuminated. The "System Status" light will blink once for every 2 seconds during normal operation. The blinking "System Status" light indicates that power is being supplied to the module. If the "System Status" light is not blinking, the diagnostic module has no power.

2. If the exhaust back pressure has exceeded 24 kPa (95 inches of H₂O) for 5% of a one hour interval, then a yellow light on the dash panel will illuminate. Note this reading in the maintenance log and continue normal operation without excess idling. No light on the diagnostic module will illuminate.

3. If the exhaust back pressure has exceeded 27 kPa (109 inches of H₂O) for 5% of a one hour interval, then the "Over Pressure" lamp (2) will illuminate. A red warning light in the cab will also illuminate. The illumination of these lights indicates that the DPF needs to be cleaned as soon as possible. The engine will stop if the back pressure exceeds 27 kPa (109 inches of H₂O).

4. If the "Over-Temperature" light is illuminated, the exhaust temperature is too high.

5. If the "System Problem" light is illuminated, then one or more sensors have failed.

6. After the DPF has been cleaned, the "Alarm Reset" button (5) on the diagnostic module must be pressed in order to reset the warning lights on the module.

Table 1

Troubleshooting Guide for the Diagnostic Monitor
Illuminated Light	Explanation
The green "System Status" is not flashing.	The diagnostic module has no power. If no noticeable loss of engine power has occurred, the vehicle may be safely driven to a Caterpillar dealer.
"System Status" light is blinking and the red "System Problem" light is illuminated.	One or more of the sensors has malfunctioned. Alert maintenance. The vehicle can be safely driven to a Caterpillar dealer.
"System Status" light is blinking. The red "Over Temperature" light is illuminated and the red "System Problem" light is illuminated.	The exhaust temperature probe has failed. Alert maintenance. The vehicle can be safely driven back to a Caterpillar dealer.
"System Status" light is flashing and the "Over Temperature" light is illuminated.	The exhaust temperature is too high. Alert maintenance. The vehicle can be safely driven to a Caterpillar dealer.
"System Status" light is blinking and the red "Over Pressure" light is illuminated.	The exhaust back pressure has exceeded operational limits. If the "Over Pressure" light on the diagnostic module is illuminated, the filter must be cleaned as soon as possible. When the red "Over Pressure" dash light illuminates, the filter must be cleaned as soon as possible. Failure to clean the filter will probably result in the derating of the engine.

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NOTICE
Operation of the engine with a plugged Diesel Particulate Filter (DPF) can lead to overheating of the exhaust system and possible vehicle damage.

The following items will cause the DPF to require cleaning more often:

• Idle times of more than 20 minutes

• Use of fuel with more than 15 ppm sulfur

• Low exhaust temperature

Do not idle for more than 20 continuous minutes.

In order to clean the DPF, refer to this Operation and Maintenance Manual, "Exhaust Particulate Filter - Clean".

For more information on testing for back pressure, refer to Systems Operation/Testing and Adjusting, RENR7572, "Air Inlet and Exhaust Systems - Inspect". This publication is included in your service manual.