What it means
The control module detects a high electrical condition in the exhaust heat exchanger exhaust bypass valve B control circuit.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
Bypass valve B directs exhaust through or around the exhaust heat exchanger. The control module monitors valve B's control circuit and sets P23A4 when its electrical signal is higher than expected, such as when the control line contacts a power supply.
Common causes
Most likely first.
- Control line shorted to supply
- Connector pins corroded - high contact resistance
- Supply wire pinched against B+ source
Symptoms
- Check-engine light on
- Exhaust heat exchanger may not bypass as commanded
- Possible change in exhaust heat management
How to diagnose it
- Record freeze-frame data and review live data for bypass valve B's command and feedback to identify when the high-circuit fault appears.
- With the exhaust cool, inspect valve B's harness for pinching or damaged insulation that could let the control wire touch a B+ source.
- Inspect the valve B connector for corrosion, loose pins, or poor contact that could disrupt the circuit.
- Use the vehicle wiring diagram to test the control line for a short to supply and check its continuity.
- If the harness and connector pass, test valve B's actuator and the module output using the manufacturer's procedure.
Common fixes
- Repair a pinched or chafed valve B control wire.
- Clean or repair corroded or loose connector terminals.
- Repair the control line short to supply.
- Replace bypass valve B or its actuator if testing confirms an internal fault.
Can I keep driving?
If the vehicle drives normally, limit driving until the circuit is checked because valve B may not manage exhaust heat as commanded. Stop if performance changes or additional warnings appear.
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.