What it means
The control module detects a low 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 controls whether exhaust flows through the exhaust heat exchanger or around it. The control module monitors valve B's electrical control circuit and sets P23A3 when the circuit signal is lower than expected, which can happen if the control line is shorted to ground.
Common causes
Most likely first.
- Control line shorted to ground
- Connector pins corroded - high contact resistance
- Harness chafing through insulation
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 check live data for bypass valve B's command and feedback to see when the low-circuit fault occurs.
- With the exhaust cool, inspect valve B's connector and harness for corrosion, damaged insulation, or chafing against nearby parts.
- Check the connector pins for corrosion, looseness, or poor contact that could increase resistance in valve B's control circuit.
- Use the vehicle wiring diagram to test valve B's control line for a short to ground and check continuity through the circuit.
- If the wiring and connections pass, test the valve actuator and module output according to the manufacturer's procedure.
Common fixes
- Repair chafed wiring in valve B's control circuit.
- Clean or repair corroded or loose connector terminals.
- Repair a control line short to ground.
- Replace bypass valve B or its actuator if testing confirms an internal fault.
Can I keep driving?
If the engine runs normally, a short trip may be possible, but avoid heavy loads until the fault is diagnosed because exhaust heat management may not work as commanded. Stop if the vehicle develops new warning lights, unusual heat, or a change in performance.
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.