Few things are more frustrating than a check engine light that spells trouble for your car’s ability to start or run smoothly. If your scan tool pulls up the P0685 code, you’re looking at an issue with your vehicle’s core electrical system: specifically, an "ECM/PCM Power Relay Control Circuit Malfunction." This code points to a breakdown in the circuit that supplies power to your engine control module (ECM) or powertrain control module (PCM)—the "brain" of your car. Ignoring it can lead to stalling, no-starts, or even unexpected shutdowns. But with the iCarsoft CR Ultra, you can diagnose and resolve P0685 without relying on a professional mechanic. Here’s how to take control.

Understanding P0685: What’s Going Wrong?

The ECM/PCM power relay is a small but critical component: it acts as a switch, sending power to the ECM/PCM when you turn the key or press the start button. When this relay or its circuit fails, the ECM/PCM can’t function properly, triggering P0685.

Common causes include:

• A worn or stuck ECM/PCM power relay (the most frequent culprit)
• Damaged wiring or loose connectors in the relay circuit
• A blown fuse protecting the ECM/PCM power supply
• Corroded relay sockets (common in older vehicles or those exposed to moisture)
• Issues with the ignition switch, which sends the signal to activate the relay

Why iCarsoft CR Ultra is Your Secret Weapon for P0685

The CR Ultra isn’t just another code reader. It’s a diagnostic workhorse designed to tackle electrical system issues like P0685 head-on. Here’s why it’s indispensable:

Step-by-Step: Fixing P0685 with iCarsoft CR Ultra

1. Confirm the Code and Gather Details

   Plug the CR Ultra into your car’s OBD-II port (usually under the dashboard) and power it on. Select your vehicle’s make, model, and year (or use AutoVIN for automatic detection). Navigate to "OBD-II" > "Read Codes" to confirm P0685 is present. Note any accompanying codes (like P0687, which relates to relay sensing) as they may offer additional clues.

2. Test the Relay Circuit Voltage

   Go to "Live Data" > "Electrical Systems" and select "ECM/PCM Relay Voltage." Turn the ignition to "On" (don’t start the engine). A healthy circuit should show voltage close to your battery’s level (around 12V). A significant drop (below 9V) indicates a problem: check for frayed wires, loose connectors, or corrosion in the relay socket.

3. Activate the Relay with Bi-Directional Controls

   Access the "Actuation Tests" menu and choose "ECM/PCM Power Relay." Use the CR Ultra to activate the relay. You should hear a distinct "click" (the relay engaging) and see voltage stabilize in live data. No click or voltage change? The relay is likely faulty and needs to be replaced.

4. Inspect Fuses and Wiring

   Use the CR Ultra’s "Component Location" feature to find the ECM/PCM relay and its associated fuse. Check the fuse for breaks (replace if blown) and inspect wiring for damage. Clean corroded connectors with electrical contact cleaner.

5. Clear the Code and Verify the Fix

   After replacing the relay, repairing wiring, or fixing connections, use the CR Ultra to "Clear Codes." Start the engine and take a 10–15 minute test drive. Re-scan with the tool to ensure P0685 doesn’t return.

Tips to Prevent P0685 from Coming Back

• Every 6 months, inspect the ECM/PCM relay socket for corrosion—especially if you live in a humid or salty environment.
• Check the relay fuse during routine oil changes; a blown fuse often precedes more serious issues.
• Use the CR Ultra’s "System Health Check" monthly to scan for early electrical faults before they trigger codes.

Don’t let a faulty relay keep you off the road. Grab your CR Ultra and get your car’s "brain" back online.