A False 1684-12 Code May Trip on Certain Tier 4 C175 Off-Highway Truck Engines {125H} Caterpillar

Mining Truck

794 AC (S/N: HRT1-UP)

Off-Highway Truck/Tractor

793F (S/N: D3T1-UP)

797F (S/N: LTZ1-UP)

Introduction

The problem that is identified below does not have a known permanent solution. Until a permanent solution is known, use the solution that is identified below.

Problem

This Technical Information Bulletin (TIB) should only be followed for the Tier 4 off-highway trucks. Tier II and LRC off-highway trucks should continue to change the high-pressure fuel pump when a 1684-12 code is displayed. If the machine experiences a 1684-12 code after a PM, fuel filling event, or other fuel system-related maintenance, the 1684-12 code may not equate to the high-pressure fuel pump being failed. The Tier 4 off-highway trucks can display this code due to air being trapped in the fuel pump.

Solution

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Do not operate or work on this product unless you have read and understood the instruction and warnings in the relevant Operation and Maintenance Manuals and relevant service literature. Failure to follow the instructions or heed the warnings could result in injury or death. Proper care is your responsibility.

To ensure that trapped air is the true cause, a Fuel System Functional Test (FSFT) should be successfully performed twice to ensure that the pump is not damaged. To correctly run the test, shutdown the engine before running the FSFT. Restart the engine, and allow the priming cycle to complete before starting the engine and running the first FSFT. To ensure that the air is removed from the system, a second FSVT should be performed If FSFT passes both times, the fuel pump is not damaged and can continue to run. If the FSFT fails both times, the pump should be replaced. If the first FSFT fails, but the second test passes. Perform a third test. If the third test passes, the pump is not failed.