Electronic Control System Signature, ISX and QSX15 Engines – Fuel Consumption Excessive

Interview the operator to verify the complaint

Refer to the Fuel Consumption-General Information and Customer Complaint Form at the end of Section TS. Follow the instructions on the form before continuing with this tree.

Operator technique is not correct

Explain correct engine operation to the operator. Refer to Operation and Maintenance Manual, Bulletin 3666251.

VE/VMS® analysis uses incorrect data

Review the VE/VMS® data and compare to the vehicle and engine specifications. Do not use more than 20 percent for the Aero value. Refer to the VE/VMS® user’s manual.

Equipment and environmental factors are affecting fuel consumption

Consider ambient temperatures, wind, tire size, axle alignment, routes, and use of aerodynamic aids when evaluating fuel consumption.

Drivetrain is not correctly matched to the engine

Check for correct gearing and drivetrain components. Refer to the OEM vehicle specifications.

Electronic fault codes active or high counts of inactive fault codes

Read the fault codes with an electronic service tool. Refer to Section TF for fault code troubleshooting.

Programmable parameters or selected features are not correct

Check the programmable parameters and the selected features with an electronic service tool. Set the parameters and features again if necessary. Refer to Procedure 019-078.

Turbocharger is not correct

Check the turbocharger part number and compare it to the Control Parts List (CPL), Bulletin 3379133 or 4021327. Replace the turbocharger if necessary. Refer to Procedure 010-033 in the Troubleshooting and Repair Manual, Signature, ISX and QSX15 Engines, Bulletin 3666239.

Fuel leak

Check the fuel lines, fuel connections, and fuel filters for leaks. Check the fuel lines to the supply tanks. Refer to the OEM service manual.

Hubometer or odometer is miscalibrated

Check the hubometer and odometer calibrations. Calibrate or replace the hubometer or odometer, if necessary. Calculate fuel consumption with new mileage figures.

Fuel grade is not correct for the application or the fuel quality is poor

Operate the engine from a tank of high-quality fuel. Refer to Fuel Recommendations and Specifications in the Operation and Maintenance Manual, Bulletin 3666251.

Lubricating oil level is above specification

Check the oil level. Verify the dipstick calibration and oil pan capacity. Fill the system to the specified level. Refer to Procedure 007-009 or 007-025 in the Troubleshooting and Repair Manual, Signature, ISX and QSX15 Engines, Bulletin 3666239.

Electronic control module (ECM) calibration is malfunctioning

Verify the electronic control module (ECM) calibration is correct. Check the calibration revision history for applicable fixes to the calibration stored in the ECM. Refer to the calibration history spreadsheet Click here to see ecm_calibration_rev_history.xls

on QuickServe® Online Internet Website or the INCAL™ calibration CD. Compare the calibration stored in the ECM with the engine rating and the Control Parts List (CPL), Bulletin 4021326 or 4021327. If necessary, recalibrate the ECM. Refer to the appropriate electronic service tool manual and Procedure 019-032.

Vehicle speed sensor (VSS) is not correct

Use an electronic service tool to monitor the vehicle speed while the vehicle is not moving. Refer to the appropriate electronic service tool manual. If necessary, install the correct VSS. Refer to Procedure 019-090 and 019-091.

Vehicle speed sensor (VSS) or circuit is malfunctioning

Check the vehicle speed sensor and circuit. Refer to Procedure 019-090 and 019-091.

Vehicle speed sensor (VSS) tampering has occurred

Check the vehicle speed sensor and circuit for tampering. Check for Fault Code 242. Repair the circuit as necessary. Refer to Procedure 019-090 and 019-091.

Air intake system restriction is above specification

Check the air intake system for restriction. Clean or replace the air filter and inlet piping as necessary. Refer to Procedure 010-031 in the Troubleshooting and Repair Manual, Signature, ISX and QSX15 Engines, Bulletin 3666239.

Exhaust system restriction is not within specification

Check the exhaust system for restrictions. Refer to Procedure 011-009 in the Troubleshooting and Repair Manual, Signature, ISX and QSX15 Engines, Bulletin 3666239.

Injector is malfunctioning

Perform the cylinder performance test. Replace injectors as necessary. Refer to Procedure 006-026 or 014-008 in the Troubleshooting and Repair Manual, Signature, ISX and QSX15 Engines, Bulletin 3666239.

Turbocharger wastegate is malfunctioning (if equipped)

Check the wastegate for correct operation. Refer to Procedure 010-050 in the Troubleshooting and Repair Manual, Signature, ISX and QSX15 Engines, Bulletin 3666239.

Overhead adjustments are not correct

Measure and adjust the overhead settings. Refer to Procedure 003-004 in the Troubleshooting and Repair Manual, Signature, ISX and QSX15 Engines, Bulletin 3666239.

Internal engine damage

Analyze the oil and inspect the filters to locate an area of probable damage. Refer to Procedure 007-002 in the Troubleshooting and Repair Manual, Signature, ISX and QSX15 Engines, Bulletin 3666239.