B1949

Code

Other B — Body

Climate Control Water Temperature Sensor Circuit Short To Ground

Brand: Other

Type: B — Body

Views: UK: 17 EN: 30 RU: 23

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Page language: EN

Causes

Damaged wiring harness (chafing, pinched, melted) causing conductor contact with ground
Corroded, bent, or loose connector pins creating a low-resistance path to ground
Failed water temperature sensor (internal short)
Aftermarket equipment or recent repairs that disturbed the HVAC harness
Short in downstream module or harness splice shared by other components

Symptoms

HVAC temperature regulation incorrect or inoperative
Climate control displays incorrect water/coolant temperature (often very low or zero)
DTC stored and possibly HVAC related warning or reduced function
Possible inability to reach desired cabin temperature rapidly

What to check

Scan for current/confirmed/pending B1949 and note freeze frame data
Visual inspection of sensor connector, wiring harness routing, and nearby contact points
Backprobe sensor signal with a DVOM or scan tool to observe voltage/live data
Check for corrosion, bent pins, or water intrusion in the connector
Verify whether other modules share the sensor circuit (splice/junction points)

Signal parameters

Sensor type: typically an NTC thermistor (resistance varies with temperature)
Nominal signal: sensor circuit is read by HVAC module via voltage divider; expected voltage varies with temperature and design (commonly within ~0.2–4.8 V range under normal conditions)
Short-to-ground signature: signal voltage near 0 V or very low and does not change with temperature
Open-circuit signature: very high resistance or sensor circuit voltage floating / out-of-range
Typical resistance behavior: resistance decreases (or increases for PTC) with temperature; refer to vehicle-specific chart for exact ohms vs °C

Diagnostic algorithm

Retrieve freeze frame and current data with a scan tool. Confirm B1949 is active or pending and note signal voltage/temperature reading.
Perform a visual inspection of the sensor, connector, and wiring harness along the entire route. Look for abrasion, heat damage, pinched sections, repairs, and water intrusion.
Unplug the sensor connector. Inspect terminals for corrosion, bent or pushed-back pins, and for evidence of a short to ground (burn marks, melted insulation).
With harness disconnected, measure resistance from the sensor signal wire (pin) to chassis ground. A short will show near 0 Ω — expected is high resistance (open) when sensor is disconnected.
Check reference voltage or pull-up at the HVAC module connector (if applicable) with key ON, engine OFF. Verify the module’s supply/reference is present and not shorted.
Measure sensor resistance directly (remove sensor if required) across sensor terminals and compare to temperature-resistance specification or the expected NTC/thermistor behavior. If resistance is near 0 Ω, sensor likely failed.
Backprobe the signal wire and monitor voltage while manipulating wiring harness (wiggle test) to reproduce fault. If voltage returns to normal when harness is moved, repair location is near that section.
If wiring appears good but short persists, trace harness to module and check splices/junctions. Disconnect other modules that share the circuit to isolate the short.
Repair or replace damaged wiring, connectors, or sensor. Use proper OEM-type connectors, heat shrink, and corrosion protection.
Clear codes and perform functional test / recheck with scan tool. Verify code does not return under normal operating conditions and that sensor readings change with temperature.

Likely causes

Water temperature sensor internal short to ground
Wiring insulation worn where harness contacts body or engine (ground)
Connector terminal corrosion bridging signal to ground
Chassis ground mistakenly connected to the signal wire during a repair

Fault status

⚠️ Status

Climate control water temperature sensor circuit short to ground detected — sensor signal held at or near ground potential. HVAC control may not receive valid temperature input.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 0.5-1.5 hours