Engine

P01BB — Engine Oil Temperature Sensor B Circuit Low

Severity: medium Drive with care, to a shop

What P01BB means

The engine control module feeds a reference voltage to oil temperature sensor B and reads the returned signal to work out oil temperature. P01BB sets when that signal falls below the expected range. This usually points to a signal wire shorted to ground or a failed sensor, leaving the ECU without reliable oil temperature data.

Symptoms

  • Check Engine Light on
  • Oil temperature reading is zero, unrealistically low or missing
  • Possible reduced power or limp mode
  • Temperature-dependent functions (such as variable valve timing or oil cooling control, if equipped) behaving oddly

Possible causes

  1. Failed oil temperature sensor B
  2. Signal wire shorted to ground (chafed insulation, damaged harness)
  3. Oil or moisture in the connector, corroded terminals
  4. Open circuit or high resistance in wiring or connectors
  5. Rarely, a reference voltage fault in the ECU or a failed ECU

How to diagnose

  1. Scan all codes and freeze frame data and look for related sensor or reference voltage codes
  2. With a cold engine, check the oil temperature reading on a scan tool; it should be close to ambient temperature
  3. Inspect the sensor, connector and harness for damage, chafing, oil contamination and corrosion
  4. Unplug the sensor: if the reading changes to open-circuit or maximum, the short is likely in the sensor
  5. With the connector and ECU disconnected, test the signal wire for a short to ground
  6. Check the reference voltage (typically about 5 V) at the sensor connector using the factory wiring diagram
  7. Measure sensor resistance and compare it to the specification for that model
  8. Clear the code after repair and confirm it does not return

Common fixes

  • Replace oil temperature sensor B
  • Repair or replace the damaged wiring harness or connector
  • Clean the terminals and remove oil from the connector
  • Fix the reference voltage circuit; repair or replace the ECU only if confirmed faulty

Questions and answers

What does P01BB mean?

It means the ECU detected a voltage that is too low in the oil temperature sensor B circuit. The most common causes are a bad sensor or a signal wire shorted to ground.

Can I drive with code P01BB?

For a short time, yes, if the engine runs smoothly and there are no other warnings. The ECU can't see true oil temperature though, so get it diagnosed soon.

This is general information about the code. The meaning can differ between makes and models: a scan tool and the repair manual for your car will show the exact cause.