Engine oil temperature sensor B internally shorted to ground or failed with a low-resistance element.; Chafed or pinched signal wire shorted to chassis ground along the harness route near hot or moving components.; Corroded, loose, or water-intruded connector at the sensor or at the PCM, causing a low-resistance path to ground.; Signal circuit shorted to a ground wire inside a shared harness splice or connector.; PCM internal fault pulling the signal line low, though this is less common than sensor or wiring issues.; Aftermarket or incorrect sensor installed that does not match the expected resistance curve for sensor B.; Oil contamination or sludge bridging sensor terminals, creating a conductive path to ground.

DTC codes / P01xx · Fuel and air metering / P01BB

P01BBEngine Oil Temperature Sensor B Circuit Low

Q: What does code P01BB mean?

Engine Oil Temperature Sensor B Circuit Low. P01BB means the powertrain control module (PCM) has detected an abnormally low voltage on the signal circuit for engine oil temperature sensor B, which is typically a second temperature sensor used for monitoring oil condition or protecting the engine. The PCM expects a voltage within a calibrated range, and a low reading usually indicates a short to ground, a faulty sensor, or a wiring problem rather than a real overheating event.

P01BB means the powertrain control module (PCM) has detected an abnormally low voltage on the signal circuit for engine oil temperature sensor B, which is typically a second temperature sensor used for monitoring oil condition or protecting the engine. The PCM expects a voltage within a calibrated range, and a low reading usually indicates a short to ground, a faulty sensor, or a wiring problem rather than a real overheating event.

SystemPowertrain

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyIntermediate

AreaFuel and air metering

Symptoms you may notice

Illumination of the check engine light (malfunction indicator lamp) with no other obvious drivability complaint.
Often no symptoms besides the warning light, especially if the sensor is only used for monitoring and not fueling or protection strategies.
An oil temperature gauge or dashboard message that reads colder than actual or stays pinned low.
Possible reduced engine power or limp mode if the PCM uses sensor B for protection strategies and sees an implausible low signal.
In rare cases, a slight change in fuel economy or cold-start behavior if the PCM substitutes a default oil temperature value.
No noticeable change in oil pressure warning behavior, since this circuit is separate from the oil pressure switch.

Common causes, most likely first

Engine oil temperature sensor B internally shorted to ground or failed with a low-resistance element.
Chafed or pinched signal wire shorted to chassis ground along the harness route near hot or moving components.
Corroded, loose, or water-intruded connector at the sensor or at the PCM, causing a low-resistance path to ground.
Signal circuit shorted to a ground wire inside a shared harness splice or connector.
PCM internal fault pulling the signal line low, though this is less common than sensor or wiring issues.
Aftermarket or incorrect sensor installed that does not match the expected resistance curve for sensor B.
Oil contamination or sludge bridging sensor terminals, creating a conductive path to ground.

How to diagnose and fix it

Scan all modules and record freeze-frame data for P01BB, then clear the code and verify whether it returns immediately or only after a drive cycle.
Visually inspect the sensor B connector and harness for corrosion, oil intrusion, chafing, and signs of a short to ground near hot or moving parts.
Disconnect the sensor and measure resistance from the signal terminal to ground; a very low reading suggests a harness short, while an open reading points to the sensor.
Back-probe the signal circuit at the PCM with the sensor connected and compare voltage to the manufacturer's expected range for the current oil temperature.
Wiggle-test the harness while watching live oil temperature B data to catch intermittent shorts that only appear under vibration or heat.
If wiring and connectors pass, replace engine oil temperature sensor B with the correct OEM-equivalent part and clear the code.
After repair, run the manufacturer's readiness drive cycle and confirm the code does not reset and live data tracks realistically as the engine warms.

What a low oil temp signal really means

A low signal voltage does not mean the engine oil is actually cold; it almost always means the circuit is being pulled toward ground by a short or a failed sensor element.
Many vehicles use sensor B for oil condition monitoring or engine protection rather than for the main temperature display, so drivers often see no drivability change and assume the code is harmless.
Technicians commonly replace the sensor first and then find a chafed harness near the exhaust or a corroded connector that was the real cause, so wiggle-testing the harness before parts swapping saves time.
A shorted sensor can sometimes be unmasked by disconnecting it and watching the live data jump to a default or open-circuit value, which confirms the harness is not the problem.
This code can be set by a low oil level or sludge condition that allows oil to bridge connector terminals, so checking oil condition and level is part of a complete diagnosis.

Can I keep driving with P01BB?

You can usually drive with P01BB if the engine runs normally and there is no oil pressure warning, but avoid heavy loads and long trips until the circuit is diagnosed. If the PCM uses sensor B for engine protection, a false low reading could trigger reduced power or missed protection, so have it checked promptly.

Tools that help

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Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.