Weak or failing 12 volt auxiliary battery giving unstable voltage readings; Damaged wiring, corrosion or loose connectors in the charger output voltage sensing circuit; Poor earth or voltage drop in the low-voltage supply or output cable; Fault in the charger or DC-DC converter's internal voltage sensing; Fault in the control module that reads the sensor signal; Outdated control unit software where the manufacturer has a known fix for this code.

P0D42

Battery Charger 14 Volt Output Voltage Sensor Circuit.

Generic
Powertrain
Generic code
Medium severity

How this code is built

P: SystemPowertrain
0: Defined bySAE, the same on every car
D: AreaReserved
42: FaultThe specific fault in that area

What it means

P0D42 indicates a fault in the sensor circuit that monitors the 14 volt output voltage of a battery charger on a hybrid or electric vehicle. This is usually the charger or DC-DC converter that supplies the low-voltage 12/14 volt system. The control unit set the code because the voltage signal was missing, implausible or outside the expected electrical range. The exact layout and which module owns the sensor depend on the model.

Symptoms

Battery or charging system warning light on the dashboard
Hybrid or electric system warning message
Low-voltage battery going flat or showing low voltage
Reduced power or the vehicle limiting its performance on some models
Vehicle failing to start or to enter ready mode
Other low-voltage electrical faults such as dim lights or erratic gauges

Possible causes

Weak or failing 12 volt auxiliary battery giving unstable voltage readingslikely
Damaged wiring, corrosion or loose connectors in the charger output voltage sensing circuitlikely
Poor earth or voltage drop in the low-voltage supply or output cablepossible
Fault in the charger or DC-DC converter's internal voltage sensingpossible
Fault in the control module that reads the sensor signalrare
Outdated control unit software where the manufacturer has a known fix for this coderare

How to diagnose

Read all stored and pending codes and note the freeze frame data, including any other charging, battery or communication codes.
Check the 12 volt battery condition and resting voltage, and inspect the terminals for tightness and corrosion.
Inspect the visible wiring and connectors for the charger or converter for chafing, water ingress, heat damage or corrosion.
Check the main earth points and the low-voltage output cable for voltage drop under load.
With a scan tool, compare the reported charger output voltage with a measured voltage at the battery.
Check the manufacturer's data for the circuit layout, expected voltage values and any software bulletins for your model.
Have a suitably trained technician carry out any testing involving the high-voltage system, following the manufacturer's isolation procedure.
Clear the code and road test to see whether it returns.

How to fix

Charge or replace the 12 volt battery if it is weak or failing.
Repair or replace damaged wiring and clean or replace corroded connectors.
Restore poor earth connections or repair high-resistance sections in the output cable.
Replace the charger or DC-DC converter if its internal voltage sensing is confirmed faulty.
Update the control unit software if the manufacturer lists it as a fix for this fault.
Repair or replace the control module only after the wiring and charger have been proven good.

Can I keep driving?

Medium severity

The vehicle may continue to run for a short time, but a charging fault can flatten the low-voltage battery and leave you stranded. Limit driving to getting it checked soon, and stop if warning lights escalate or power is lost.

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