Powertrain, generic (extended)

P2B4B B Camshaft Position Actuator Position Sensor B Circuit Bank 2

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

P2B4B is set when the circuit feeding the second position sensor (B) of the exhaust actuator on bank 2 is open or otherwise unusable. Bank 2 exists only on engines with two cylinder rows, such as the Mercedes M176/M177 V8, whose CAMTRONIC bulletin lists exhaust feedback faults on bank 2 for sensor A (P34C1, P34C2) but not for sensor B. No manufacturer has published a description of P2B4B, so the diagnosis follows the general pattern: check plug, wires and sensor supply, then the sensor in the actuator. Mercedes also found heat damage on the harness above the bulkhead on these engines. CARB expects electronic parts of valve-lift systems to be monitored for circuit faults. Bank 1 exhaust counterpart: P2B47.

Likely causes

Plug or wires at the actuator open
Heat damage to the harness above the bulkhead
Sensor in the exhaust actuator failed

Symptoms

  • Check engine light on
  • Cylinder deactivation or exhaust lift change unavailable
  • Somewhat higher consumption

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€80–700
Time0.5–3.5 h

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

Parts involved

b camshaft position actuator pos sensor b b2wiring harnessecm

Related codes

P2B43P2B47P2B4CP2B4DP2B4EP34C0

References: law.cornell.edu, ntn-snr.com, static.nhtsa.gov.