A short to ground or chafed wire on the sensor power supply B circuit; Corroded, loose, or damaged connector at the sensor or PCM; A failed sensor internally shorting the reference voltage to ground; Open circuit or high resistance in the power supply wiring or a splice; Faulty powertrain control module (PCM) driver for the B circuit; Water intrusion or contamination in a connector causing voltage drop

DTC codes / P06xx · Computer and output circuits / P06B4

P06B4Sensor Power Supply B Circuit Low

Q: What does code P06B4 mean?

Sensor Power Supply B Circuit Low. P06B4 indicates that the powertrain control module (PCM) has detected a low voltage condition on the power supply circuit designated as 'B' for a sensor or sensor group. This circuit typically provides a regulated 5-volt or 12-volt reference to components such as the mass airflow sensor, throttle position sensor, or manifold absolute pressure sensor, and a low reading means the PCM sees less voltage than expected on that feed.

P06B4 indicates that the powertrain control module (PCM) has detected a low voltage condition on the power supply circuit designated as 'B' for a sensor or sensor group. This circuit typically provides a regulated 5-volt or 12-volt reference to components such as the mass airflow sensor, throttle position sensor, or manifold absolute pressure sensor, and a low reading means the PCM sees less voltage than expected on that feed.

SystemPowertrain

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyIntermediate

AreaComputer and output circuits

Symptoms you may notice

Illumination of the check engine light, often with no other noticeable symptoms
Rough idle or stalling if the affected sensor loses its reference voltage
Reduced engine performance or limp mode in some vehicles
Poor fuel economy or increased emissions due to incorrect sensor readings
Intermittent hesitation or surging during acceleration
Other sensor-related codes stored alongside P06B4

Common causes, most likely first

A short to ground or chafed wire on the sensor power supply B circuit
Corroded, loose, or damaged connector at the sensor or PCM
A failed sensor internally shorting the reference voltage to ground
Open circuit or high resistance in the power supply wiring or a splice
Faulty powertrain control module (PCM) driver for the B circuit
Water intrusion or contamination in a connector causing voltage drop

How to diagnose and fix it

Use a scan tool to record freeze-frame data and check for related codes that pinpoint which sensor circuit is affected
Inspect the wiring harness and connectors for the sensor power supply B circuit for chafing, corrosion, or loose pins
Disconnect the affected sensor and measure reference voltage at the connector with the key on; compare to specification
Perform a voltage drop test on the power supply wire from the PCM to the sensor to locate excessive resistance
Check for shorts to ground on the power supply wire with a multimeter or test light
If the circuit tests good, substitute a known-good sensor to see if the code returns
If all external circuits and sensors are ruled out, diagnose the PCM driver circuit or replace the PCM as a last resort

What the B circuit really feeds

The 'B' designation does not refer to a specific sensor; it is one of several power supply outputs from the PCM, so the same code can point to different components on different makes and models.
A common oversight is replacing the sensor first when the actual fault is a rubbed-through wire behind the engine or near a sharp bracket.
This code can set intermittently due to vibration or temperature changes, so a wiggle test of the harness while monitoring live data is often more revealing than a static voltage check.
Some vehicles share the B circuit among multiple sensors, so a single shorted sensor can pull down the reference for others and set multiple codes.
A weak battery or charging system fault can cause low reference voltage readings that mimic a circuit problem, so always verify system voltage first.

Can I keep driving with P06B4?

You can usually drive the vehicle to a repair shop, but avoid heavy acceleration or long trips because a failed sensor reference can cause stalling or limp mode. If the engine runs poorly or stalls, stop driving and have it towed to prevent unsafe conditions.

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.