01 From Tires to Driveshafts: An Expert Explains Why Your Car … • 02 Steering Wheel Feels Loose? Uneven Tire Wear? Don't Ignore … • 03 Decoding Dashboard Lights: 50 Common Indicators, Causes, an… • 04 P0062, P0063, and P0064: HO2S Heater Control Circuit (Bank … • 05 Why You Need to Press the Brake Pedal When Shifting from P … • 06 What Do Pilots Say When Crashing? The Truth Behind the Words • 07 How Often Should You Drive Your Car to Keep It in Good Shap… • 08 What Happens When a Pilot Misses the Landing on US Aircraft… • 09 Fix This First If Your Car Won’t Start (Before Calling a Me… • 10 Tyre Burst At High Speed: What To Do And How To Stay Safe •

DTC codes / P05xx · Vehicle speed, idle control and auxiliary inputs / P05FB

P05FBStop-Start Status Signal Circuit High

P05FB means the engine control module (ECM) has detected a high voltage condition on the stop-start status signal circuit, which is the wire that tells the module whether the vehicle's automatic stop-start system is active, inhibited, or faulted. The ECM expects a specific voltage range on this signal line, and a reading above the normal threshold indicates an open circuit, a short to voltage, or a failed component on that signal path.

SystemPowertrain
Code typeGeneric (all makes)
SeverityLow
Fix difficultyIntermediate
AreaVehicle speed, idle control and auxiliary inputs

Symptoms you may notice

  • The stop-start system does not engage, so the engine never shuts off at traffic lights or in stop-and-go traffic.
  • A warning light or message on the dashboard indicates the stop-start system is unavailable or disabled.
  • The engine may restart immediately after an auto-stop event, or the system may refuse to shut down the engine at all.
  • Often no symptoms besides the warning light, because the vehicle otherwise drives normally.
  • In some vehicles, the stop-start button or indicator flashes or stays illuminated to show the system is inhibited.
  • Fuel economy may drop slightly because the engine idles instead of shutting off during stops.

Common causes, most likely first

  1. A damaged or disconnected stop-start status signal wire, often from chafing, corrosion, or a loose connector at the battery current sensor or stop-start module.
  2. A failed stop-start status switch or button that sends an incorrect high-voltage signal to the ECM.
  3. Corrosion or water intrusion in the connector or harness near the battery, starter, or body control module (BCM).
  4. A faulty battery current sensor or battery monitoring sensor that shares the stop-start status circuit and pulls the signal high.
  5. An open circuit in the signal return path, causing the ECM to see a high voltage on the signal line.
  6. A short to voltage on the signal wire from another circuit in the same harness, often after body repairs or accessory installation.
  7. A failed stop-start control module or ECM, though this is the least likely cause and should only be suspected after all wiring and component checks pass.

How to diagnose and fix it

  1. Scan all modules for stored codes and freeze-frame data, then clear codes and test-drive to confirm P05FB returns before proceeding.
  2. Visually inspect the stop-start status signal circuit wiring and connectors for chafing, corrosion, loose pins, or water intrusion, especially near the battery and underhood fuse box.
  3. Disconnect the stop-start status switch or sensor and check the signal voltage at the connector with a digital multimeter (DMM) to see if the high voltage is present with the component removed.
  4. Perform a voltage drop test on the signal circuit and its ground return to rule out excessive resistance in the harness or connectors.
  5. Check for technical service bulletins (TSBs) or software updates for the stop-start system, as some manufacturers have revised calibration or wiring repairs for this code.
  6. If the signal circuit tests good, substitute a known-good stop-start status switch or sensor and recheck the code.
  7. As a last step, diagnose the stop-start control module or ECM for internal faults only after all external wiring and components have been verified.

What the stop-start status signal really does

  • The stop-start status signal is often a low-current square wave or a voltage divider signal, so a standard test light can damage the circuit; always use a high-impedance digital multimeter.
  • A weak or aging battery can cause the stop-start system to set this code because the battery monitoring sensor reports an incorrect status, even when the signal wire itself is intact.
  • Many technicians replace the stop-start switch or module without checking the battery current sensor, which shares the same signal circuit on some platforms and can pull the voltage high.
  • This code can be set by a completely unrelated aftermarket accessory wired into the same harness, such as a dash camera or remote starter, creating a short to voltage on the signal line.
  • P05FB does not always mean the stop-start system is broken; a intermittent connector fault can set the code once and never return, so a thorough wiggle test of the harness is essential.

Can I keep driving with P05FB?

The vehicle remains safe to drive because the stop-start system is a fuel-saving feature and does not affect engine power, braking, or steering. You can continue driving, but avoid relying on the stop-start function and have the circuit inspected when convenient to prevent a no-start condition if the fault worsens.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

Running on fumes Free guides aren't free to make. Top up the tank. Any amount, one time. Fuel the Garage