What is Caterpillar CAT320 Fault Code 1956-13?

Fault Code 1956-13 indicates an "Injector Cylinder 6 - Out of Calibration" error on the Caterpillar 320 excavator. This diagnostic trouble code (DTC) is triggered when the Electronic Control Module (ECM) detects that the fuel injector for cylinder 6 is operating outside its programmed calibration parameters during active fuel delivery.

This code specifically relates to the common rail fuel injection system used in CAT 320 models equipped with C6.4 or C7.1 ACERT engines. The ECM continuously monitors injector performance by comparing actual fuel delivery against expected values stored in the injector's trim code or calibration data. When cylinder 6's injector deviates beyond acceptable tolerances, the system logs this FMI-13 (Failure Mode Identifier 13) fault. This is critical because improper fuel delivery causes power imbalance, increased emissions, incomplete combustion, and potential long-term engine damage—especially problematic in used excavators where injector wear accelerates from accumulated operating hours.

Common Symptoms

• Check Engine Light or malfunction indicator lamp illuminated on the instrument cluster
• Noticeable rough idle or engine vibration, particularly at low RPM
• Loss of power or reduced hydraulic performance during digging or lifting operations
• Black or gray exhaust smoke indicating incomplete combustion from cylinder 6
• Increased fuel consumption as the ECM attempts to compensate for the faulty injector

Potential Causes

The most common technical causes for Code 1956-13 on used CAT320 excavators include:

• Worn or contaminated fuel injector on cylinder 6 due to high operating hours or poor fuel quality
• Incorrect injector calibration codes entered into the ECM after previous injector replacement
• Faulty injector solenoid causing erratic fuel metering and delivery timing
• Damaged injector wiring harness or corroded connectors—common on used machines where harness routing near the valve cover experiences heat cycling and vibration
• Low fuel pressure from a failing high-pressure fuel pump or restricted fuel filters
• ECM software issues requiring reprogramming or updates specific to injector trim codes

How to Troubleshoot and Fix Code 1956-13

Step 1: Verify Fault Code and Injector Calibration Data Connect Caterpillar Electronic Technician (CAT ET) diagnostic software to the machine's diagnostic port. Confirm Code 1956-13 is active, then navigate to the injector calibration section to verify that cylinder 6's trim code matches the physical injector installed. On used excavators, mismatched codes from previous repairs are common and cause false calibration faults.

Step 2: Inspect Wiring Harness and Connectors Physically inspect the injector harness for cylinder 6, focusing on areas where the harness contacts the valve cover or engine block—known rub points on CAT320 models. Check the injector connector for corrosion, bent pins, or moisture intrusion. Use a digital multimeter to measure resistance across the injector solenoid (typically 0.3-0.7 ohms) and check for continuity to ground, which indicates harness damage.

Step 3: Test Fuel System Pressure and Injector Performance Using CAT ET, perform an injector cutout test to isolate cylinder 6 and observe engine behavior changes. Measure common rail fuel pressure with the engine running (should maintain 1,600-1,800 bar under load). If pressure is low, inspect the high-pressure fuel pump and replace fuel filters. For used machines with over 8,000 hours, injector mechanical wear is likely—consider sending the injector for flow bench testing or replacement.

Step 4: Reprogram or Replace Components If calibration codes are correct and wiring is intact, the injector likely requires replacement. After installing a new injector, immediately program the new trim code into the ECM using CAT ET. Clear fault codes and perform a regeneration cycle to ensure proper operation.

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Disclaimer: This guide provides general troubleshooting information. Always consult the official Caterpillar service manual for your specific machine serial number and consider professional diagnostic services for complex fuel system repairs.