What is Case CX210C Fault Code P1112?

Fault Code P1112 on the Case CX210C excavator indicates an Intake Air Temperature (IAT) Sensor Circuit High Voltage condition. This diagnostic trouble code (DTC) is triggered when the Engine Control Module (ECM) detects an abnormally high voltage signal (typically above 4.8-4.9 volts) from the intake air temperature sensor circuit, suggesting either an open circuit, damaged sensor, or wiring fault.

The IAT sensor plays a critical role in the Case CX210C's Isuzu engine management system by monitoring incoming air temperature. The ECM uses this data to calculate proper fuel injection timing and air-fuel ratios. When P1112 is active, the ECM operates in a failsafe mode using default temperature values, which can reduce engine efficiency, increase emissions, and potentially cause performance issues in varying ambient conditions.

Common Symptoms

• Check Engine Light or malfunction indicator lamp illuminated on the instrument cluster
• Reduced engine power or noticeable loss of throttle response, especially during cold starts
• Hard starting conditions in cold weather due to incorrect fuel delivery calculations
• Rough idle or increased fuel consumption as the ECM compensates with default air temperature values
• Black smoke from exhaust during acceleration due to overly rich fuel mixture

Potential Causes

The most common causes of P1112 on used Case CX210C excavators include:

• Open circuit in sensor wiring caused by harness chafing near the intake manifold or engine vibration points
• Failed IAT sensor with internal open circuit (common in machines with 5,000+ operating hours)
• Corroded or loose connector pins at the sensor or ECM connection points, especially on machines exposed to moisture
• Damaged wiring harness from rodent activity or previous improper repairs
• Faulty ECM (rare, but possible in high-hour machines with voltage spike history)

How to Troubleshoot and Fix Code P1112

Step 1: Visual Inspection Locate the IAT sensor on the intake manifold or air inlet housing. Inspect the sensor connector and wiring harness for visible damage, corrosion, bent pins, or oil contamination. On used excavators, check for harness rub points along the valve cover and near engine mounts where vibration causes wear.

Step 2: Sensor Resistance Testing Disconnect the IAT sensor connector. Using a digital multimeter, measure resistance across the sensor terminals. At 68°F (20°C), resistance should typically read 2,000-3,000 ohms (consult Case service manual for exact specifications). An open circuit (infinite resistance) confirms sensor failure.

Step 3: Circuit Voltage Testing With ignition ON and sensor disconnected, check supply voltage at the harness connector. You should see approximately 5 volts on the signal wire. If voltage reads near battery voltage (12V+), suspect a short to power in the harness. If no voltage exists, trace wiring back to the ECM connector checking for breaks.

Step 4: Repair or Replace Replace the IAT sensor if resistance is out of specification. For used machines, always apply dielectric grease to connector pins before reassembly to prevent future corrosion. If wiring is damaged, repair using OEM-spec wire and proper heat shrink connections—avoid electrical tape in engine compartments.

Disclaimer: This guide provides general troubleshooting information. Always consult the Case CX210C service manual and consider professional diagnostic assistance for complex electrical issues or ECM-related problems.