Unlike the circuit codes, P23A5 judges the result: the module commanded valve B, the second exhaust bypass at the heat exchanger, but it does not see the response it expects, for example in position feedback or in how the exhaust-side coolant temperatures change. No manufacturer publishes P23A5. Ford's handling of valve A shows how such a check can mislead: for P237F on F-150, Explorer, Escape and Maverick full hybrids up to 2024, SSM 52543 first has the connectors of exhaust coolant temperature sensors 3 and 4 inspected for water or corrosion, and TSB 24-2173 cures false P237F on 2024 Mavericks with a PCM update. CARB requires a functional check of output components. Driving is usually unaffected; P23A6 and P23A7 name a flap stuck in one position.
Medium severity. Can I keep driving?You can usually keep driving in the short term. If you smell exhaust fumes in the cabin, stop driving and ventilate the car.
Symptoms
- Check engine light on
- Cabin heat slow to arrive in winter
- No effect on drivability
Most likely causes
- Flap of valve B sluggish from soot or corrosion
- Exhaust coolant temperature sensor connector wet or corroded, distorting the plausibility check
- Worn actuator gearing or linkage
- Overly strict calibration, fixed by a software update
What to check, in order
Start with the simplest. You can tick off each step.
Good to know
- Repair difficulty: medium
- It affects emissions.
What each character of P23A5 means
- P: Powertrain: engine and transmission
- 2: Generic code: same on every make
- 3: Ignition and misfires
- A5: Specific fault in that system
Frequently asked questions
Can I keep driving with code P23A5?
You can usually keep driving in the short term. If you smell exhaust fumes in the cabin, stop driving and ventilate the car.
What causes code P23A5?
The most common causes are: flap of valve B sluggish from soot or corrosion; exhaust coolant temperature sensor connector wet or corroded, distorting the plausibility check; worn actuator gearing or linkage.
Related codes
- P23A2Exhaust Heat Exchanger Exhaust Bypass Valve B Control Circuit/Open
- P23A6Exhaust Heat Exchanger Exhaust Bypass Valve B Stuck Open
- P23A7Exhaust Heat Exchanger Exhaust Bypass Valve B Stuck Closed
- P23A8Exhaust Heat Exchanger Exhaust Bypass Valve B Position Sensor Stop Performance
- P237FExhaust Heat Exchanger Exhaust Bypass Valve A Control Performance
Sources
Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.