What is Caterpillar 336D2 Fault Code 39:1657-3?

Fault Code 39:1657-3 indicates a voltage problem with the Hydraulic Pump Solenoid #2 circuit, specifically a high voltage condition detected by the Engine Control Module (ECM). This code means the ECM has detected an abnormally high voltage signal on the control circuit for the secondary hydraulic pump's proportional solenoid valve.

In the Caterpillar 336D2 excavator, the hydraulic pump solenoid regulates hydraulic flow and pressure based on operator demand and engine load. When the ECM detects voltage above the specified threshold (typically above 4.8-5.0 volts when normal operating range is 0.5-4.5 volts), it triggers this fault to protect the system. This is critical because improper hydraulic pump control can lead to reduced machine performance, excessive fuel consumption, and potential damage to hydraulic components. The 336D2's Electronic Hydraulic Control System relies on precise voltage signals to optimize productivity and fuel efficiency.

Common Symptoms

• Reduced hydraulic power or sluggish boom/arm/bucket movements during combined functions
• Yellow warning light illuminated on the instrument cluster with fault code displayed
• Engine derating or limited RPM in some cases to protect the hydraulic system
• Erratic hydraulic response where pump output doesn't match operator input
• Increased fuel consumption due to improper pump displacement control

Potential Causes

The most common causes for fault code 39:1657-3 on used Caterpillar 336D2 excavators include:

• Damaged or chafed wiring harness near the main pump area where cables rub against the frame or rotating components (common wear point after 5,000+ hours)
• Corroded or loose electrical connectors at the pump solenoid due to hydraulic oil contamination or moisture intrusion
• Failed hydraulic pump solenoid valve with internal short circuit causing voltage spike
• ECM internal fault or corrupted software calibration (less common but possible on older machines)
• Shorted wiring between the solenoid and ECM, often from pinched cables during previous service work
• Aftermarket component incompatibility if the solenoid was previously replaced with non-OEM parts

How to Troubleshoot and Fix Code 39:1657-3

Step 1: Visual Inspection Begin by inspecting the wiring harness running from the ECM to Hydraulic Pump Solenoid #2 (located on the main hydraulic pump assembly). On used excavators, check specifically for harness wear where cables pass near rotating pump drives or sharp frame edges. Look for oil-soaked connectors, frayed insulation, or pinched wires from previous repairs.

Step 2: Connector and Resistance Testing Disconnect the solenoid connector and inspect for corrosion, bent pins, or hydraulic fluid contamination. Using a digital multimeter, measure the resistance across the solenoid terminals—specification is typically 3-7 ohms for Cat pump solenoids. Also check for shorts to ground by measuring resistance between each solenoid terminal and chassis ground (should read open circuit/infinite resistance).

Step 3: Voltage Signal Testing With the connector still disconnected and ignition ON (engine OFF), measure voltage at the ECM-side harness connector. You should see approximately 5 volts reference voltage. If voltage reads above 5.5 volts with the solenoid disconnected, the problem is in the wiring or ECM. If voltage normalizes when disconnected, the solenoid is likely failed internally.

Step 4: Harness Continuity Check Check continuity and resistance through the entire harness between ECM and solenoid. Pay special attention to harness routing—on used machines, previous technicians may have rerouted cables improperly. Resistance should be less than 5 ohms total for the circuit.

Step 5: Component Replacement and Verification If the solenoid tests faulty, replace with genuine Caterpillar parts (part number specific to 336D2 model year). Clear the fault code using Caterpillar Electronic Technician (Cat ET) diagnostic software and perform a functional test under load. For wiring issues, repair or replace the affected harness section using proper sealed connectors and protective sleeving.

Disclaimer: This guide provides general diagnostic information. Always consult the official Caterpillar service manual for your specific machine serial number and consider professional diagnosis, especially for complex electrical issues or machines under warranty.