B1947

Climate Control A/C Post Evaporator Sensor Circuit Short To Ground

Body Engine Cooling A/C Evaporator Sensor 🟢 Low — Fix at next service ✅ Safe to Drive
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What This Actually Means

In plain language — no jargon

The A/C evaporator temperature sensor after the cooling coil has shorted to ground, meaning the electrical signal line is touching metal and draining to 0 volts. Think of it like a water pipe that's punctured and leaking all its water instead of flowing properly.

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Symptoms You May Notice

3 known symptoms for this code
A/C compressor won't engage or cycles on/off erratically
Climate control displays incorrect temperature or no temperature reading
Engine may run rough or A/C blows warm air
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How Your ECU Detects This

Technical sensor logic and voltage thresholds

The ECU monitors the post-evaporator temperature sensor's voltage output, which should vary between 0.5–4.5V depending on coil temperature (typically 0–15°C). A short to ground pulls the signal line to 0V continuously, preventing the ECU from reading actual temperature and disabling A/C control logic.

Voltage & Parameter Thresholds

ParameterNormal RangeFault Condition
Sensor voltage 0.5–4.5V (varies with temperature) 0.0V (shorted to ground)
Evaporator temperature 0–15°C during operation Cannot be determined due to short circuit
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Diagnostic & DIY Fix Guide

Check these in order — from cheapest to most complex
1
Wiring harness connector
Inspect connector pins at evaporator sensor for corrosion or moisture; clean with electrical contact cleaner and reseat firmly.
2
Post-evaporator temperature sensor
Unplug the sensor and test resistance to ground using a multimeter; replace if shorted (typically located near evaporator outlet).
3
Wiring and insulation
Trace sensor signal wire from evaporator to ECU for cuts, abrasions, or pinches causing grounding; repair or replace damaged wire.
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When to See a Professional Mechanic

Not all fault codes are safe to DIY

Code B1947 is a low-severity fault. Your vehicle is generally safe to drive to a workshop for diagnosis. However, do not ignore it indefinitely — low-severity codes often indicate developing problems that become expensive if neglected. Book a diagnostic appointment within 2–4 weeks. If you notice any additional symptoms (rough running, power loss, unusual smells), treat it as higher priority.

Safety note: OBD-II codes identify the system or circuit where a fault was detected — they do not always identify the exact failed component. A professional mechanic using live sensor data will diagnose the root cause more accurately than replacing parts based on the code alone.
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How to Clear Code B1947

What happens after you fix the fault

Once the fault is repaired, B1947 can be cleared using any OBD-II scanner. Connect the scanner, navigate to "Clear Codes" or "Erase DTCs," and confirm. The check engine light turns off immediately.

The code will return if the root cause was not actually fixed. The ECM re-detects the fault within 1–3 drive cycles and sets the code again.

✅ Safe to Clear When
  • Fault has been diagnosed and repaired
  • You want to confirm the repair worked
  • Code appeared after a sensor was cleaned
⚠️ Do Not Clear When
  • Preparing for an emissions/PUC test
  • Root cause is still undiagnosed
  • Check engine light is flashing
Emissions test note: Clearing codes resets OBD readiness monitors. Most vehicles need 50–100 km of mixed driving before monitors complete. Do not clear codes immediately before an emissions or PUC inspection.