P1625

What Does Code P1625 Mean?

DTC P1625 signifies a “B+ Supply To VCRM Fan Circuit Malfunction.” The Powertrain Control Module (PCM), often referred to as the Engine Control Module (ECM), monitors the electrical integrity of numerous circuits within the vehicle’s powertrain and auxiliary systems. In this specific instance, the PCM has detected an anomalous voltage condition on the primary Battery Positive (B+) supply circuit to the Variable Cooling Fan Control Module (VCRM). The VCRM is an essential component responsible for precisely regulating the speed of the electric cooling fan(s) based on various inputs such as engine coolant temperature, air conditioning system pressure, and vehicle speed, as commanded by the PCM. The PCM sets P1625 when it perceives that the dedicated B+ input voltage to the VCRM is either absent, intermittently low, or outside of its predetermined operational range for a specified duration, indicating a loss or degradation of the module’s primary power source. This directly impairs the VCRM’s ability to receive power and, consequently, its capacity to activate and control the engine cooling fans, leading to potential engine overheating and compromised HVAC performance.

Common Symptoms

• Engine Overheating: Especially prevalent during idle, low-speed driving, or in heavy traffic, as insufficient airflow over the radiator leads to an inability to dissipate heat.
• Air Conditioning System Malfunction: The A/C system may blow warm air or cool inefficiently, particularly at low vehicle speeds, due to the condenser fan not operating to shed heat.
• Cooling Fan Inactivity: The electric cooling fan(s) may not engage at all when commanded by the PCM.
• Illuminated Malfunction Indicator Lamp (MIL): The Check Engine Light will be illuminated on the dashboard.
• Reduced Engine Performance: Some vehicle systems may enter a “limp-home” mode to prevent engine damage from overheating, resulting in decreased power and restricted RPMs.

What Causes the Code P1625?

• Blown Fuse: A blown fuse within the B+ supply circuit to the VCRM is a very common cause, interrupting the constant battery voltage.
• Open Circuit or High Resistance in Wiring: Damaged, chafed, or corroded wiring between the battery/power distribution center and the VCRM can create an open circuit or introduce excessive resistance, leading to insufficient voltage reaching the module.
• Corroded or Loose Electrical Connectors: Faulty terminals or poor connections at the VCRM harness connector or other inline connectors can impede B+ supply.
• Faulty Variable Cooling Fan Control Module (VCRM): An internal electrical fault within the VCRM itself could prevent it from drawing or correctly registering its B+ supply, even if the external wiring is intact.
• Faulty Power Distribution Center (PDC) or Fuse Box: Internal issues within the PDC, such as corroded terminals or a failing relay socket (if applicable), can disrupt the VCRM’s B+ supply.
• Corroded Battery Terminals or Cables: Severe corrosion or loose connections at the battery can affect overall system voltage stability and lead to inadequate supply to critical modules.

How to Diagnose and Troubleshoot

Diagnosis of P1625 requires meticulous electrical system testing using a digital multimeter (DMM) and a vehicle-specific wiring diagram.

1. Retrieve and Verify DTCs: Connect an OBD-II scanner to confirm P1625 is present. Note any other accompanying codes that might indicate related electrical issues. Clear the code and observe if it immediately returns or if the symptoms are reproducible.
2. Visual Inspection: Begin by visually inspecting the cooling fan assembly, the VCRM, and all associated wiring harnesses and connectors for obvious signs of damage, chafing, corrosion, or loose connections. Pay close attention to the main power supply wire leading to the VCRM.
3. Battery and Charging System Check: Ensure the battery is fully charged (typically 12.6V or higher) and that the charging system (alternator) is functioning correctly. Inspect battery terminals for cleanliness and tightness.
4. Fuse Inspection: Locate the fuse(s) for the VCRM or cooling fan module in the under-hood fuse box or power distribution center using the vehicle’s service manual. Use a DMM to test for continuity across the fuse. A visual check alone is often insufficient. Replace any blown fuses. If a newly installed fuse blows immediately, a direct short circuit exists somewhere in the VCRM circuit.
5. VCRM B+ Supply Voltage Test:
   • Disconnect the VCRM electrical connector.
   • With the ignition OFF, use a DMM to measure the voltage between the designated B+ terminal on the VCRM wiring harness connector (refer to the wiring diagram for the precise pin) and a known good chassis ground.
   • You should observe continuous battery voltage (approximately 12.6V or more).
   • If voltage is absent or significantly low (e.g., less than 10V), proceed to trace the B+ wire back towards its power source (battery, fuse box, or relay).
6. Voltage Drop Test on B+ Supply Wire:
   • This test identifies high resistance in the B+ supply circuit. Connect one lead of your DMM to the positive battery terminal and the other lead to the B+ terminal of the VCRM harness connector (with the connector still disconnected from the VCRM).
   • Start the engine (if possible and safe, ensuring no danger from disconnected components).
   • A voltage drop exceeding 0.2 volts indicates excessive resistance in the B+ supply wire, necessitating repair or replacement of that section of wiring.
7. VCRM Ground Circuit Test: While P1625 specifically points to B+ supply, a poor ground can mimic or contribute to voltage issues. With the VCRM disconnected, measure the resistance between the VCRM ground terminal on the harness connector and a known good chassis ground point. Resistance should be very low (typically less than 0.5 ohms).
8. VCRM Internal Fault Assessment: If all B+ supply and ground circuits test perfectly, but the VCRM is not activating the fans, the VCRM itself is highly suspect. Some scan tools offer bidirectional control to command the VCRM or fans, which can aid in confirming module functionality.

Recommended Repairs and Solutions

Addressing P1625 typically involves specific electrical repairs or component replacement, focusing on restoring a reliable B+ supply to the VCRM.

• Fuse Replacement and Short Circuit Repair: If a blown fuse is identified, replace it with a fuse of the correct amperage. If the new fuse blows, meticulously trace the B+ supply circuit using the wiring diagram to locate and repair the short circuit. This often involves inspecting wiring for chafing against metal components or internal shorts within the VCRM.
• Wiring and Connector Repair/Replacement: Repair any identified open circuits, high-resistance points, or short circuits in the VCRM’s B+ supply wiring. This may necessitate splicing in new sections of wire using appropriate automotive-grade butt connectors and heat-shrink tubing, or replacing corroded/damaged connector terminals. Ensure all repairs are robust and weatherproof.
• Clean and Secure Battery/Ground Connections: Clean any corrosion from the battery terminals and ensure they are tightly fastened. Similarly, inspect and clean the VCRM’s chassis ground connection point, ensuring it is free of paint, rust, and is securely torqued.
• Variable Cooling Fan Control Module (VCRM) Replacement: If the B+ supply, ground, and PCM command signals to the VCRM are all confirmed to be operating correctly, but the VCRM is still failing to function or has an internal short, replacing the VCRM is the appropriate solution. Ensure the replacement module is the correct part number for the specific vehicle application. Note that on some vehicles, the VCRM is integrated directly into the cooling fan assembly, requiring replacement of the entire unit.
• PCM Replacement (Rare): PCM failure resulting in a false P1625 code is exceedingly rare. This should only be considered as a last resort after all other possible causes have been meticulously diagnosed and ruled out. PCM replacement often requires specialized programming and calibration.

Mechanic’s Tip: Always disconnect the negative battery terminal before performing any electrical repairs or component replacements to prevent accidental shorts. After completing repairs, clear the DTCs and perform a thorough test drive, monitoring engine temperature and cooling fan operation with a scan tool to confirm the issue is resolved and the code does not return.