What Does P06B4 Mean?
The sensor power supply circuit "B" is reporting a voltage lower than the minimum expected threshold. The 5V reference B line is being pulled low, likely by a shorted sensor or a wire grounding out. All sensors powered by this circuit will report inaccurate low readings, causing the PCM to make incorrect fuel, timing, and transmission decisions.
Common Causes
40%
One sensor on the 5V reference B circuit has an internal short to ground
25%
Wiring short to ground on the 5V reference B supply wire due to harness damage
20%
PCM internal 5V voltage regulator degradation on the B supply
10%
Corroded or water-damaged connector on the B reference circuit
5%
Aftermarket device drawing excessive current from the reference B line
Diagnostic Steps
1
Measure the 5V reference B voltage at the PCM connector — compare to the specification of 4.95V-5.05V and document the actual value.
2
Disconnect all sensors on the reference B circuit one at a time while monitoring voltage — if voltage recovers when a specific sensor is disconnected, that sensor is shorted internally.
3
If voltage is still low with all sensors disconnected, check the wiring harness for a ground short by measuring resistance from the 5V reference B wire to chassis ground.
4
Inspect connectors on the B circuit for green corrosion, moisture, or bent pins — particularly in areas exposed to road spray.
5
If the PCM output measures low with nothing connected, the internal regulator has failed and the PCM requires replacement or rework.
Estimated Repair Cost
$75 - $1,200
Parts + labor, varies by vehicle and location
The sensor power supply circuit "B" is reporting a voltage lower than the minimum expected threshold. The 5V reference B line is being pulled low, likely by a shorted sensor or a wire grounding out. All sensors powered by this circuit will report inaccurate low readings, causing the PCM to make inco...
The most common cause of P06B4 (Sensor Power Supply "B" Circuit Low) is: One sensor on the 5V reference B circuit has an internal short to ground
Typical repair costs for P06B4 range from $75 to $1,200, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Low reference voltage on the B circuit causes multiple sensors to read incorrectly, resulting in poor fuel mixture, potential misfires, and stalling risk. Limit driving until diagnosed.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P06B4 to identify the root cause.
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Quick Info
Category
Powertrain
System
Sensor Reference Voltage / Engine Control
Difficulty
Type
Generic (SAE)
Recommended Tools
OBD2 Scanner
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