Powertrain, generic (extended)

P2A39 O2 Sensor Positive Current Control Circuit Low Bank 1 Sensor 3

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

P2A39 is set when the pump-current lead feeding the rearmost wide-band probe on bank 1 (sensor 3) is pulled below its permitted window, typically because the wire rubs through to chassis ground near the hot rear exhaust section. At ignition-on Saab's 2010 9-5 shows roughly 2.8 V on the pump-current pins of its front probe, so a reading near zero points to a ground short. No manufacturer publishes P2A39 itself; Ford stores a short to ground on the IP wire of its front probes under P0131, and CARB only requires that such out-of-range signals be caught. P2A38 covers the open line, P2A3A the high side, P22AC the sensor 2 case. Apart from the warning lamp, the aftertreatment monitors using this probe stay incomplete.

Likely causes

Pump-current wire chafed through to body or exhaust bracket
Internal short in the probe after thermal shock or water ingress
Faulty sensor interface in the engine control module

Symptoms

  • Check engine light after repeated detection
  • Sensor 3 reading implausible or missing in live data

Repair estimate

DifficultyMediumDIY possible
Parts and labour€50–450
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

P2A38P2A3AP2A3CP22ACP0143

References: saabwisonline.com, newtonnet.co.uk, law.cornell.edu.