What it means
The ECM detects an open or blown fuse on the ignition coil primary supply circuit B. Affected coils receive no operating voltage.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
- The engine or gearbox may go into limp mode
How it works
The ignition coil primary supply feeds the low-voltage side of the coils so the ECM can switch them to create spark. For circuit B, the ECM detects that the shared supply fuse is open or has blown, leaving the coils on that feed without operating voltage.
Common causes
Most likely first.
- Primary supply fuse blown by short circuit
- Shorted ignition coil drawing excess current
Symptoms
- Check-engine light
- Rough running or misfire
- Poor acceleration
- Hard starting
How to diagnose it
- Read freeze-frame data and misfire counts to identify when the fault occurred and whether affected cylinders share ignition supply B.
- With the ignition off, locate and inspect the fuse identified for ignition coil primary supply B in the vehicle's service information.
- If the fuse is open, inspect circuit B wiring and coil connectors for chafing, damaged insulation, moisture, or a short to ground before replacing it.
- Check the coils supplied by circuit B for a short or abnormal current draw using the manufacturer's procedure.
- After repairing a found fault, fit the specified fuse and verify that circuit B has supply voltage and the code does not return.
Common fixes
- Repair damaged or chafed wiring that is shorting ignition supply B.
- Replace a shorted ignition coil on the circuit B feed.
- Clean and secure a damaged coil power connector.
- Replace the circuit B fuse with the specified type after correcting the cause of the open fuse.
Can I keep driving?
A misfire can damage the catalytic converter, and a severe misfire or hard starting can make the vehicle unsafe in traffic. Avoid hard acceleration and long trips; stop if the engine runs very roughly or the check-engine light flashes.
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.