B150C4B

Code

VOLVO B — Body

Parking Heater Module. Over Temperature

Brand: VOLVO

Type: B — Body

Views: UK: 19 EN: 37 RU: 21

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Page language: EN

Causes

Faulty/heavily inaccurate heater temperature sensor (NTC/thermistor)
Restricted airflow or blocked intake/exhaust around the heater unit
Coolant flow restriction (airlock, closed thermostat, blocked coolant passages) causing local overheating
Low coolant level or coolant pump failure
Heater fan or combustion blower not running
Wiring fault (open/short/poor ground) to the temperature sensor or heater module

Symptoms

Parking heater shuts down or will not run
Driver information message or warning lamp related to parking heater
Reduced or no cabin pre-heating
Stored fault B150C4B (Over Temperature)
Possible noticeable smell of overheated components or hot coolant (take care)

What to check

Read all stored and pending DTCs and freeze-frame data with a capable scan tool
Visually inspect heater unit, air intake/exhaust and surrounding area for soot, debris or restrictions
Check coolant level and condition in the expansion tank with the engine cold
Inspect electrical connectors to heater module and temperature sensor for corrosion, damage or looseness
Measure supply voltage to heater module (expected ~11–14.5 V with ignition on/run)
Confirm heater fan/blower and coolant pump operation while attempting heater run (observe operation or use scan tool outputs)

Signal parameters

Heater temperature sensor reading — expected range typically 0–120 °C; over-temperature threshold often in the 100–130 °C range (manufacturer-specific)
Temperature sensor resistance/voltage — verify against specification (NTC: resistance falls as temp rises; typical signal 0.5–4.5 V depending on circuit)
Module supply voltage — 11–14.5 V with engine/aux power on
Heater fan/blower command and actual RPM or current draw — verify fan responds to module commands
Coolant pump command and current draw — pump should run when commanded
CAN/serial communications — module should be communicative on vehicle network (no bus errors)

Diagnostic algorithm

Retrieve DTCs and freeze frame/operational data. Note ambient and reported heater temperature at fault time.
With ignition/aux power off, visually inspect heater unit, intake and exhaust for obstruction, soot or damage. Clear debris if present.
Check coolant level and top if low. Inspect for leaks. If low, pressure-test cooling system per manual.
Inspect all connectors and wiring for the temperature sensor, fans, pump and module. Repair any damage or poor contacts.
With a scan tool, attempt to run the parking heater while monitoring temperature sensor value, fan/pump commands, module supply voltage and any status messages. If heater is disabled, note module outputs.
Measure the heater temperature sensor with a multimeter (resistance) or by backprobing signal voltage; compare to ambient and service specification. If sensor reading is implausible, replace sensor.
Verify airflow: command the heater fan on and confirm airflow from intake and exhaust. Repair/replace fan or remove blockages if fan does not operate.
Verify coolant circulation through the heater (feel hoses, use temperature gun) while heater/pump runs. Repair pump, thermostat or clear airlocks as required.
Check fuses/relays and measure current draw of heater components for signs of internal short or overload.
If mechanical and sensor checks are good but over-temperature persists, update module software if available and/or replace the heater control module following manufacturer's procedures.
Safety note: allow the heater and coolant to cool before touching. Follow manufacturer service manual and safety procedures when working with fuel-burning auxiliary heaters.

Likely causes

Heater temperature sensor failure or bad connector
Blocked airflow or exhaust at the heater
Coolant circulation problem local to the heater
Heater fan or pump not operating
Module hardware failure

Fault status

⚠️ Status

Parking heater exceeded safe operating temperature. Module logged B150C4B and may disable heater until fault is resolved.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.0 - 3.0 hours

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