B150812

Code

VOLVO B — Body

Inside Temperature Sensor 5V supply. Circuit Short To Battery

Brand: VOLVO

Type: B — Body

Views: UK: 21 EN: 31 RU: 25

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Page language: EN

Causes

Wiring shorted to battery (pinched/chafed harness contacting B+ conductor)
Corroded or bridged connector causing B+ to feed the 5V supply line
Faulty inside temperature sensor (internal short)
Failed climate control / HVAC control module driving the 5V reference
Aftermarket accessories or repairs that spliced into the wrong wire
Water intrusion in connector or harness causing conductive path to battery

Symptoms

DTC B150812 (or related HVAC sensor supply faults) stored
Interior temperature displayed incorrectly (max/high) or frozen value
Climate control behaving incorrectly (incorrect automatic climate regulation)
Loss of accurate cabin temperature readings in HVAC screen or instrument cluster
Possible blown fuses for HVAC circuits or erratic HVAC module behavior

What to check

Read DTCs and freeze frame data with a capable scan tool; record live sensor voltage and module reported supply voltage
Visually inspect the inside temperature sensor, connector, and wiring for damage, corrosion, or water contamination
With ignition ON (engine off), backprobe the sensor connector and measure the reference supply voltage and sensor output voltage
Disconnect the sensor harness and measure the 5V reference at the harness connector to see if it is still at battery voltage (indicates short upstream)
Check continuity between the 5V reference pin and battery positive to confirm short; check continuity to module pin to isolate location
Inspect for aftermarket splices or repairs in the circuit routing

Signal parameters

Expected 5V reference at sensor connector: approx. 4.75–5.25 V with ignition ON (varies by model)
Battery voltage at B+ circuits: approx. 11.5–14.5 V (engine running)
Normal sensor output (analog) depends on sensor type/temperature, typically 0.3–4.7 V — consult OEM chart
If shorted to battery the sensor/reference may measure near battery voltage (~12 V) on the 5V line
Ground continuity:
Sensor resistance (if NTC thermistor): varies with temperature (example nominal ~2k–100kΩ depending on temperature and sensor design) — use OEM spec sheet

Diagnostic algorithm

Connect scan tool, record B150812, freeze frame and live data for inside temperature sensor and 5V supply readings.
Visually inspect sensor and harness for damage, corrosion, pinched sections, or signs of water ingress; repair obvious wiring/connectors first.
With ignition OFF, disconnect the inside temperature sensor connector. Inspect pins for corrosion or bridging.
With ignition ON (engine off for safety), backprobe the harness side 5V reference pin and measure voltage. Expected ~5V. If ~12V, there is a short to battery upstream — DO NOT reconnect sensor until repaired.
If 5V is high, trace the wiring toward the HVAC module and battery to locate the short. Disconnect connectors in sections and re-test to isolate the segment with the high voltage.
If 5V at the harness is normal (~5V) and sensor output is abnormal, measure the sensor resistance or sensor output vs temperature (compare to OEM table). Replace sensor if out of spec.
If harness and sensor check good but code persists, test the HVAC/control module supply and grounding. Repair or replace module if module output fault is confirmed by OEM procedures.
After repair or replacement, clear codes and verify by cycling ignition and road/functional test to confirm code does not return.
If diagnostic steps are inconclusive, consult OEM wiring diagrams and technical service bulletins for model-specific faults or repair procedures.

Likely causes

Chafed/abraded harness where 5V reference passes near battery/12V source
Corrosion or conductive contamination in the sensor connector
Defective inside temperature (ambient) sensor with internal short to battery potential
Shorted pin in HVAC control module connector or internal module fault

Fault status

⚠️ Status

Inside temperature sensor 5V supply circuit shorted to battery (B+). 5V reference is reading excessive voltage indicating a short to battery or failed component.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 0.5-2.0 hours

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