What is Case CX210C Fault Code P0122?

Fault Code P0122 on the Case CX210C excavator indicates "Throttle Position Sensor/Accelerator Pedal Position Sensor A Circuit Low Input." This diagnostic trouble code (DTC) is triggered when the Engine Control Module (ECM) detects an abnormally low voltage signal from the Throttle Position Sensor (TPS) or Accelerator Pedal Position Sensor (APPS), typically below 0.17 volts for more than one second.

The TPS/APPS is critical for proper engine operation on the CX210C, as it communicates the operator's power demand to the ECM. This sensor provides a variable voltage signal (typically 0.5-4.5 volts) that corresponds to pedal position. When this signal drops below the manufacturer's threshold, the ECM cannot accurately determine engine load requirements, directly impacting fuel delivery, throttle response, and hydraulic system performance. For used excavators operating in demanding conditions, this code can severely limit productivity and potentially cause unsafe operating conditions.

Common Symptoms

• Check Engine Light or malfunction indicator lamp illuminated on the instrument cluster
• Reduced engine power or noticeable loss of throttle response, even at full pedal depression
• Engine operating in limp mode or derate, limiting maximum RPM to 1200-1500 range
• Erratic idle or engine stalling when attempting to increase throttle input
• Sluggish hydraulic response due to insufficient engine power output during operations

Potential Causes

The most common technical causes for P0122 on used Case CX210C excavators include:

• Faulty Throttle Position Sensor or Accelerator Pedal Position Sensor (internal wiper track wear or circuit failure)
• Damaged wiring harness between the sensor and ECM, particularly at known rub points near the engine firewall and undercarriage routing
• Corroded or loose electrical connectors at the sensor plug or ECM connection points (common in machines exposed to moisture)
• Short circuit to ground in the signal wire, often caused by insulation breakdown from age and vibration
• Low supply voltage from the ECM to the sensor due to faulty voltage regulator or poor ground connections
• Failed ECM (less common but possible in high-hour used machines with previous electrical issues)

How to Troubleshoot and Fix Code P0122

Step 1: Visual Inspection Begin by thoroughly inspecting the accelerator pedal assembly and associated wiring harness. On used excavators, check for physical damage, frayed wires, or evidence of harness rubbing against metal components near the pedal mounting area and along the frame rail toward the ECM. Inspect all connector pins for corrosion, bent terminals, or moisture intrusion—particularly the 6-pin connector at the pedal sensor.

Step 2: Voltage and Resistance Testing Using a digital multimeter, perform a backprobe test at the TPS/APPS connector with the key in the ON position (engine off). Verify the 5-volt reference supply from the ECM (typically Pin 1). Check the signal wire voltage (Pin 2) at idle pedal position—it should read approximately 0.5-0.9 volts. Slowly depress the pedal while monitoring; voltage should smoothly increase to 4.0-4.5 volts at full depression. Any reading below 0.3 volts or erratic jumps confirm sensor failure. Also measure sensor ground circuit resistance (Pin 3 to battery negative)—it should be less than 5 ohms.

Step 3: Harness Continuity and Isolation Disconnect both the sensor and ECM connectors. Test continuity between sensor connector pins and corresponding ECM pins to identify open circuits. Check for shorts to ground by measuring resistance between each signal wire and chassis ground (should be infinite resistance/OL). For used machines, pay special attention to wire routing through the cab floor and engine compartment bulkhead where vibration-induced wear commonly occurs.

Step 4: Component Replacement and Verification If testing confirms sensor failure, replace the Throttle/Accelerator Pedal Position Sensor with a genuine Case OEM part or quality equivalent. After replacement, clear the fault code using Case diagnostic software (ServiceMaster or equivalent scan tool) and perform a pedal relearn procedure if required by the ECM. Test operate the machine under load to verify proper throttle response and confirm the code does not return.

Disclaimer: This guide provides general diagnostic information for Case CX210C excavators. Always consult the manufacturer's official service manual and consider professional diagnostic assistance for complex electrical issues. Improper repairs can result in further damage or unsafe machine operation.