Caterpillar 305C CR Fault Code 122:168-1: Complete Diagnostic Guide

What is Caterpillar 305C CR Fault Code 122:168-1?

Fault Code 122:168-1 indicates a data erratic/intermittent signal from the Engine Speed/Timing Sensor (FMI 1 - data valid but erratic or intermittent). This code specifically relates to the crankshaft position sensor or engine speed sensor sending inconsistent signals to the Electronic Control Module (ECM).

This fault is critical for the Caterpillar 305C CR because the ECM relies on precise engine speed data to control fuel injection timing, engine performance, and emissions systems. When the signal becomes erratic, the engine cannot operate at optimal efficiency, potentially leading to performance degradation or complete shutdown to prevent engine damage.

Common Symptoms

When fault code 122:168-1 is active, operators typically experience:

• Intermittent engine stalling or rough idling, especially during warm-up or under load
• Check Engine Light illuminated on the instrument panel with possible derate mode activation
• Difficulty starting the engine, requiring multiple cranking attempts
• Loss of power or hesitation during hydraulic operations and digging cycles
• Engine RPM fluctuations visible on the tachometer without throttle input changes

Potential Causes

The most common technical causes for this fault code in used Caterpillar 305C CR excavators include:

• Worn or damaged crankshaft position sensor due to heat exposure and vibration over time
• Corroded or loose electrical connectors at the sensor harness connection point
• Damaged wiring harness from rubbing against engine components or frame rails (common wear point near the flywheel housing)
• Contaminated sensor face from oil leaks, metal debris, or excessive dirt buildup
• Incorrect air gap between the sensor and flywheel teeth due to mounting bracket wear
• Failing ECM (less common, but possible in high-hour machines)

How to Troubleshoot and Fix Code 122:168-1

Step 1: Visual Inspection Begin by locating the engine speed sensor near the flywheel housing on the engine block. Inspect the wiring harness for visible damage, chafing, or oil contamination. Check the connector for corrosion, bent pins, or moisture intrusion—common issues in used excavators exposed to harsh environments.

Step 2: Electrical Testing Using a digital multimeter, measure the sensor's resistance (typically 200-1000 ohms for magnetic sensors). Check the signal voltage while cranking the engine; you should see an AC voltage signal fluctuating between 0.5-5 volts. Inspect the harness continuity from sensor to ECM, checking for resistance above 5 ohms indicating wire damage.

Step 3: Physical Sensor Inspection Remove the sensor and examine the sensing tip for metal shavings, cracks, or oil buildup. Verify the air gap specification (typically 0.020-0.050 inches) between the sensor and flywheel teeth using feeler gauges. For used machines, check the flywheel teeth for damage or excessive wear that could cause erratic signals.

Step 4: Component Replacement If testing confirms sensor failure, replace with a genuine Caterpillar sensor and apply dielectric grease to connector terminals. Clear the fault code using Caterpillar ET diagnostic software and perform a test run under load.

Disclaimer: This guide provides general diagnostic information. Always consult the official Caterpillar service manual for your specific serial number and consider professional diagnosis for complex electrical issues or if you lack proper diagnostic tools.