What is Caterpillar Fault Code SPN1570?

SPN 1570 indicates a malfunction in the Diesel Exhaust Fluid (DEF) Pump Motor Circuit on Caterpillar equipment equipped with Selective Catalytic Reduction (SCR) aftertreatment systems. This Suspect Parameter Number (SPN) specifically monitors the electrical performance of the DEF pump motor, which is responsible for delivering precise amounts of diesel exhaust fluid into the exhaust stream to reduce NOx emissions.

This fault code is critical because the DEF injection system is essential for meeting EPA Tier 4 Final emissions standards. When SPN 1570 is active, the Engine Control Module (ECM) detects abnormal current draw, voltage irregularities, or complete circuit failure in the DEF pump motor. Left unresolved, this code can trigger engine derate modes, significantly reducing your excavator's power output and productivity on the jobsite.

Common Symptoms

• Amber or red DEF system warning light illuminated on the instrument cluster
• Engine power derate (typically 25-40% power reduction) after a countdown timer expires
• Frequent DEF system-related fault codes appearing simultaneously (such as SPN 1761 or SPN 3031)
• DEF pump motor not audible during key-on self-test (normally produces a brief whirring sound)
• Increased diesel consumption due to incomplete aftertreatment regeneration cycles

Potential Causes

The most common technical causes for SPN 1570 on used Caterpillar excavators include:

• DEF pump motor failure due to crystallized DEF contamination or internal motor winding breakdown
• Corroded or damaged wiring harness connections at the DEF pump module (especially on machines operating in corrosive environments)
• Chafed or pinched wires along the frame rail where the DEF harness routes near moving components
• ECM internal driver circuit failure (less common but possible on high-hour machines)
• Poor ground connections at the DEF system ground points or corroded chassis ground straps
• Contaminated DEF fluid causing pump seizure or excessive current draw

How to Troubleshoot and Fix Code SPN1570

Step 1: Initial Inspection Using Caterpillar Electronic Technician (Cat ET) diagnostic software, verify the fault code is active and check for additional related codes. Inspect the DEF pump assembly for physical damage, crystallized DEF residue around connections, or obvious harness damage. On used excavators, pay special attention to harness routing near the DEF tank mounting area where vibration and rubbing commonly occur.

Step 2: Electrical Testing Disconnect the DEF pump motor connector and inspect pins for corrosion, bent terminals, or moisture intrusion. Using a digital multimeter, check for proper supply voltage (typically 12V) at the pump connector with the key on. Measure the motor winding resistance (typically 2-6 ohms depending on pump model) to verify the motor hasn't failed internally. Check continuity of all wires back to the ECM and verify ground circuit integrity (should read less than 0.5 ohms resistance to chassis ground).

Step 3: Component Testing and Repair If voltage and ground circuits test correctly, perform a current draw test while commanding the DEF pump active through Cat ET software. Normal operating current is typically 3-8 amps; readings significantly higher indicate pump seizure or contamination. For used machines, drain and inspect DEF fluid quality—cloudy or contaminated fluid indicates the entire system requires flushing. Replace the DEF pump module if internal motor failure is confirmed, and always replace wiring harness connectors showing any corrosion. After repairs, clear codes and perform a complete SCR system self-test through diagnostic software to verify proper operation.

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Disclaimer: This guide provides general diagnostic information for SPN 1570. Always consult the official Caterpillar service manual for your specific machine model and serial number. If you're uncomfortable performing electrical diagnostics or working with emissions systems, contact a certified Caterpillar technician to prevent further damage to expensive aftertreatment components.