Powertrain, generic (extended)

P23A4 Exhaust Heat Exchanger Exhaust Bypass Valve B Control Circuit High

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modeNo

P23A4 is stored when the control circuit of exhaust heat exchanger bypass valve B reads higher than expected – a short to a battery feed, a chafed wire touching another supply, or an actuator whose electronics pull the line up. Because the flap no longer obeys, the warm-up strategy has to run without it. There is no public manufacturer documentation for P23A4. Ford names the valve A counterpart P237E only once, in SSM 53003 for 2021–2023 F-150 hybrids with the 3.5L PowerBoost, together with the position sensor codes P2C22 and P2C23, and replaces the heat exchanger actuator. CARB requires circuit checks on emission-related output components. P23A3 is the low-side fault and P23A2 the open circuit; a high reading seldom clears by itself.

Likely causes

Control wire shorted to a 12 V feed in the harness
Failed electronics inside the valve B actuator
Output stage in the controlling module faulty

Symptoms

  • Check engine light on
  • Bypass flap does not respond to an actuator test
  • Driving behaviour unchanged

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€50–900
Time0.5–3 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

exhaust bypass valve bexhaust heat recovery actuator

Related codes

P23A2P23A3P23A5P237E

References: law.cornell.edu, static.nhtsa.gov.