P0B3A: Motor Electronics Coolant Pump B Control Circuit High

P0B3A sets when the control signal of motor electronics coolant pump B stays higher than expected, typically a short to battery voltage on the command line or, with some driver designs, an open pump input that floats high. The module then cannot switch the pump as requested. No manufacturer documents P0B3A publicly. As reference points, FCA has a pump B on its 4xe models with the performance code P0C74, and Ford lists the pump A high code P0A07 among PCM codes fixed by a battery controller update on the 2020 Explorer and Aviator hybrids. CARB requires inverter thermal management outputs to be monitored. Open and low faults are P0B38 and P0B39. Overheating protection may reduce power.

Medium severity. Can I keep driving?Watch the temperature gauge. If it climbs or a warning appears, stop the car in a safe place and turn off the engine: overheating can cause serious damage.

Symptoms

MIL and hybrid or coolant warning
Pump cannot be switched off or on as commanded
Reduced electric power when the inverter heats up

Most likely causes

Control wire shorted to battery voltage
Pump control input open so the line floats high
Controller software misjudging the circuit, fixed by update
Driver stage in the controlling module faulty

What to check, in order

Start with the simplest. You can tick off each step.

With the engine cold, check the coolant level; never do this when the system is hot
Check the sensor's ground and make sure the signal wire is not receiving voltage from another circuit.
Check the actual temperature in live data
Make sure the fan comes on when it should
Check the thermostat and connector
Measure the sensor and replace it if its readings do not make sense

Good to know

Repair difficulty: medium
It can trigger limp mode.
It affects emissions.

What each character of P0B3A means

P: Powertrain: engine and transmission
0: Generic code: same on every make
B: Subsystem depends on the code range
3A: Specific fault in that system

Frequently asked questions

Can I keep driving with code P0B3A?

Watch the temperature gauge. If it climbs or a warning appears, stop the car in a safe place and turn off the engine: overheating can cause serious damage.

What causes code P0B3A?

The most common causes are: control wire shorted to battery voltage; pump control input open so the line floats high; controller software misjudging the circuit, fixed by update.

Related codes

Sources

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.