What is Yanmar General Fault Code P1433-3?

Fault Code P1433-3 indicates a Secondary Air Injection System Pump Control Circuit malfunction with an intermittent or erratic signal detected by the Engine Control Module (ECM). This code specifically relates to the secondary air pump's electrical circuit, which is responsible for injecting fresh air into the exhaust system during cold starts to reduce emissions and facilitate diesel particulate filter (DPF) regeneration.

In Yanmar excavators, the secondary air injection system plays a critical role in meeting emissions standards and maintaining optimal exhaust aftertreatment performance. When the ECM detects irregular voltage patterns, open circuits, or intermittent connections in the pump control circuit, it triggers P1433-3. This fault can compromise the machine's ability to perform active regeneration cycles, potentially leading to reduced engine performance and increased emissions output.

Common Symptoms

• Check Engine Light (CEL) or malfunction indicator lamp illuminated on the instrument panel
• DPF regeneration failures or more frequent regeneration cycles than normal
• Intermittent power derate or engine performance reduction during cold starts
• Rough idling or hesitation immediately after starting the engine
• Abnormal sounds from the secondary air pump area, including clicking or buzzing noises when the system attempts activation

Potential Causes

The most common technical reasons for P1433-3 in used Yanmar excavators include:

• Corroded or damaged wiring harness connections at the secondary air pump relay or pump connector (common wear points near engine mounting brackets)
• Failed secondary air injection pump motor due to carbon buildup or bearing seizure
• Faulty pump control relay or relay socket with burnt contacts
• ECM internal driver circuit degradation (less common but possible in high-hour machines)
• Chafed wiring along the frame rail where harnesses contact sharp edges during machine vibration
• Poor ground connections at the pump mounting bracket or chassis ground points
• Intermittent voltage supply issues from the main power distribution center

How to Troubleshoot and Fix Code P1433-3

Step 1: Visual Inspection Begin by thoroughly inspecting the secondary air pump wiring harness from the ECM to the pump assembly. On used excavators, pay special attention to areas where the harness routes near moving components or sharp metal edges. Look for wire insulation damage, connector corrosion (white or green deposits), and loose terminals. Check the pump mounting bolts for tightness, as loose mounts can cause ground circuit issues.

Step 2: Electrical Testing Using a digital multimeter, check for proper voltage supply at the pump connector with the ignition on (should read battery voltage, typically 12-24V depending on system). Test the ground circuit resistance (should be less than 1 ohm to chassis ground). Disconnect the pump connector and measure the pump motor resistance across its terminals (typically 2-5 ohms for most Yanmar applications). Significantly higher readings indicate motor winding failure.

Step 3: Relay and Circuit Verification Locate the secondary air pump relay in the main fuse/relay box. Swap it with an identical relay to rule out relay failure. Using Yanmar diagnostic software or a compatible OBD-II scanner, perform an active test to command the pump on/off while monitoring voltage at the pump connector. Intermittent voltage drops during this test confirm wiring issues rather than component failure.

Step 4: Component Replacement and Verification If wiring and connections are intact, replace the secondary air pump assembly. For used machines, always replace the pump connector pigtail simultaneously, as repeated connection cycles degrade terminal tension. After repairs, clear codes, perform a cold start cycle, and monitor for code recurrence over several operating hours.

---

Disclaimer: This guide provides general diagnostic information for Yanmar excavators. Always consult the manufacturer's service manual for your specific model and serial number. If you lack proper diagnostic tools or experience with high-voltage systems, seek assistance from a certified Yanmar technician or qualified heavy equipment mechanic.