What it means
Voltage on the secondary starter relay control line is below the expected window. Wiring faults of this kind typically come from chafing, water ingress at connector seals, or pin push-back — a wiggle test on the harness while the code is active often confirms the location.
At a glance
- Usually lights the check-engine light
How it works
Starter relay B controls a secondary starter circuit, such as a dedicated stop-start starter, and the module monitors voltage on its relay control line. This low-circuit code sets when the line voltage falls below the expected range, often from a short to ground or a shorted relay coil.
Common causes
Most likely first.
- Control wire shorted to ground
- Internal short in relay coil
- Connector pins corroded - high contact resistance
Symptoms
- Engine may crank slowly or fail to start
- Stop-start function may be unavailable
- A starter or powertrain warning light may appear
How to diagnose it
- Use a scan tool to capture freeze-frame data and check for companion starter or stop-start codes that may point to a shared supply or control fault.
- Check battery condition and connections, then verify whether the engine cranks slowly, fails to start, or has a stop-start warning.
- Inspect relay B, its socket, and the control harness for rubbed insulation, water, corrosion, or terminals that are loose or pushed back.
- With the wiring diagram, test the control line for a short to ground and check relay coil resistance using the manufacturer's procedure.
- If the circuit and relay pass, check the module command and output at the specified test points.
Common fixes
- Repair the control wire shorted to ground.
- Clean or repair corroded or loose terminals at relay B and its connector.
- Replace relay B if its coil is internally shorted or it fails the specified test.
- Repair the module control circuit if its output remains low with sound wiring and relay.
Can I keep driving?
The engine may not start reliably, and stop-start may be disabled. Avoid repeated cranking if the starter turns slowly, since that can overheat the starter and cables.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.