Short to ground in the wiring of a sensor fed from reference voltage B; Faulty sensor with an internal short that pulls the shared 5 volt supply down (for example a pressure, position or pedal sensor, depending on model); Chafed, damaged or water-contaminated wiring harness or connector causing a short or high resistance leak to ground; Corroded or loose connector terminals or poor earth connections affecting the sensor supply; Faulty engine control unit with a failed internal 5 volt regulator; Aftermarket wiring or accessories interfering with the sensor circuits.

P0652

Sensor Reference Voltage B Circuit Low.

Generic
Powertrain
Generic code
Medium severity

How this code is built

P: SystemPowertrain
0: Defined bySAE, the same on every car
6: AreaComputer and output circuits
52: FaultThe specific fault in that area

What it means

P0652 means the engine control unit has detected that the 5 volt sensor reference supply known as circuit B is lower than expected. Several sensors share this supply, so a short to ground or an overloaded supply pulls the voltage down. Which sensors are on reference B depends on the vehicle, so check the wiring diagram for the specific model and engine.

Symptoms

Malfunction indicator lamp on
Poor running, hesitation or lack of power
Rough idle or engine stalling
Engine in limp mode with reduced power
Erratic or implausible readings from several sensors at once
Possible hard starting or no start

Possible causes

Short to ground in the wiring of a sensor fed from reference voltage Blikely
Faulty sensor with an internal short that pulls the shared 5 volt supply down (for example a pressure, position or pedal sensor, depending on model)likely
Chafed, damaged or water-contaminated wiring harness or connector causing a short or high resistance leak to groundpossible
Corroded or loose connector terminals or poor earth connections affecting the sensor supplypossible
Faulty engine control unit with a failed internal 5 volt regulatorrare
Aftermarket wiring or accessories interfering with the sensor circuitsrare

How to diagnose

Read all stored codes and freeze frame data, noting any other sensor circuit codes that point to a shared supply
Check the wiring diagram to identify which sensors share reference voltage B on this model and engine
Visually inspect the harness, connectors and earth points for chafing, water ingress, corrosion or previous repair damage
With the ignition on, measure the reference supply voltage at a sensor connector and compare it with the specification of about 5 volts
Unplug the sensors on that supply one at a time and watch whether the voltage recovers; the one that restores it is the likely culprit
Test the harness for short to ground and for resistance between the supply wire and earth with the control unit and sensor disconnected
Check the power and earth supplies to the control unit before suspecting the unit itself
Clear the code and road test, rechecking for the fault to confirm the repair

How to fix

Replace the sensor that is pulling the reference voltage down
Repair or replace the damaged wiring or connector where a short to ground is found
Clean or repair corroded terminals and restore poor earth connections
Remove or correct any faulty aftermarket wiring on the affected circuits
Repair or replace the engine control unit only after the wiring and sensors are proven good, following the manufacturer procedure

Can I keep driving?

Medium severity

The car may be driven carefully for a short time, but power loss, stalling or limp mode can occur without warning, so get it diagnosed soon. Avoid driving if it stalls or loses power, as that could be unsafe in traffic.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.