Powertrain, generic (extended)

P2A38 O2 Sensor Positive Current Control Circuit/Open Bank 1 Sensor 3

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modeNo

P2A38 reports that the lead carrying positive current control for bank 1's third oxygen sensor has no continuity. That sensor sits behind a second converter or a later aftertreatment stage, and the code only makes sense where this position carries a wide-band probe: through this lead (pin APE/IP on a Bosch LSU 4.9) the controller drives between about −2 and +2.25 mA into the pump cell. No manufacturer documents P2A38 publicly. For the upstream twin P2237, Ford's 2012 summary spots a broken IP wire because lambda barely moves during deliberate reference-current pulses; its own third sensors are switching types with heater codes only. P2A39/P2A3A are the low/high faults, P2A3B the open return. The lamp lights, while driving feels unchanged.

Likely causes

Broken pump-current wire or pushed-back pin in the sensor plug
Sensor plug loose or not latched after exhaust work
Internal break in the pump cell of the probe

Symptoms

  • Check engine light
  • Sensor 3 value frozen near lambda 1 in live data
  • Downstream emission monitors not completed

Repair estimate

DifficultyMediumDIY possible
Parts and labour€0–450
Time0.5–2.5 h

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

Parts involved

oxygen sensor b1s3wiring harnessecm

Related codes

P2A39P2A3AP2A3BP22ABP2237P0142

References: newtonnet.co.uk, bosch-motorsport.com, law.cornell.edu.