B1947 — Climate Control A/C Post Evaporator Sensor Circuit Short To Ground

Is it safe to drive with B1947?

Safe to drive. EVAP faults affect emissions, not drivability — you can keep using the car while planning the repair. Fuel vapour smell is a reason to fix it sooner: vapours are flammable and harmful.

What does OBD2 code B1947 mean?

OBD2 code B1947 flags a problem with the evaporative emission (EVAP) system (climate control A/C post evaporator sensor circuit short to ground). The car is usually drivable while you plan the repair. Common culprits: loose, damaged or wrong fuel cap, faulty purge valve (canister purge solenoid), faulty vent valve or leak detection pump.

Will B1947 clear itself?

Sometimes B1947 clears after a few drive cycles if the fault was intermittent — for example a loose connector or a tank of bad fuel. The underlying cause usually remains, so the code tends to return. Clear it once; if it comes back, diagnose rather than erase it repeatedly.

How much does it cost to fix B1947?

Replace the fuel cap — $20–$60; Replace the purge or vent valve — $120–$350; Replace the charcoal canister — $250–$700. Exact cost depends on the root cause, your vehicle and local labor rates — a proper diagnosis is the cheapest first step.

What are the symptoms of B1947?

Drivers most often notice: no noticeable driving symptoms in most cases, fuel smell near the car, especially after refueling, slightly worse fuel economy, difficulty refueling (nozzle clicks off).

When your vehicle's diagnostic system stores trouble code B1947, it's alerting you to a problem with the climate control system's post-evaporator temperature sensor. Specifically, the powertrain or body control module has detected that the sensor circuit is shorted to ground — meaning an unintended electrical path is pulling the signal voltage down to chassis ground. This sensor plays a critical role in how your HVAC system manages cooling; it tells the module the temperature of the air leaving the evaporator core so the system can regulate blower speed, blend door position, and A/C clutch engagement accurately. When the module sees a short circuit instead of a proper temperature signal, it sets B1947 and often defaults the A/C to limited or no operation.

The module doesn't set B1947 from a single momentary glitch. It requires the fault condition to appear repeatedly under specific operating conditions — typically with the engine running and the climate control system powered up. When the code stores, the freeze frame data captures engine load, RPM, coolant temperature, and vehicle speed at that exact moment. That snapshot gives you a starting point: replicate those conditions during testing to trigger the fault reliably.

B1947 falls within the body electrical category, not the powertrain category. That distinction matters because it means the issue lives in your vehicle's comfort and accessory systems rather than in the engine or transmission. While the Check Engine light may illuminate, the fault won't affect your engine's ability to run, accelerate, or stop. The real impact is on cabin comfort and, in some cases, defrost performance.

Symptoms of B1947

• Check Engine light or A/C warning indicator illuminated on the instrument cluster
• A/C system refuses to turn on or shuts off unexpectedly
• Weak, inconsistent, or only warm airflow from the vents
• Excessive window fogging due to incorrect humidity regulation
• Unusual fan cycling behavior — the blower may run at full speed or not at all
• In rare cases, battery drain from the module trying to compensate for the sensor fault

Common Causes of B1947

The most frequent culprit behind B1947 is a failed post-evaporator temperature sensor. Over time, these sensors can suffer internal short circuits, especially in high-heat and high-humidity environments under the dash. Beyond the sensor itself, several other failures can create the same circuit-short-to-ground condition.

• Faulty post-evaporator temperature sensor with internal short circuit
• Wiring harness damage — chafed, melted, or broken wires in the sensor circuit, often from heat exposure or improper assembly
• Corroded or loose electrical connector at the sensor or module
• Ground fault elsewhere in the HVAC control circuit that mimics a sensor short
• Aftermarket alarm or accessory installation that tapped into the sensor wiring incorrectly
• Rarely, a faulty body control module outputting incorrect ground reference

How to Diagnose B1947

Before replacing parts, confirm the fault with systematic checks. Rushing to replace the sensor wastes money when the real problem lies elsewhere.

1. Connect an OBD2 scanner, record B1947, and save the freeze frame data. Note engine RPM, load, coolant temperature, and speed captured when the code set — you'll want to reproduce these conditions during your test drive.
2. Check for any other stored codes. Related sensor failures, module faults, or short circuits elsewhere can produce B1947 as a secondary code. Addressing the root code first often clears the B1947 as well.
3. Inspect the sensor wiring and connector visually. Pull back the harness cover near the evaporator housing (typically behind the glove box or under the dash) and look for cracked insulation, melted wires, green corrosion, or pins that are bent, pushed out, or loose.
4. Test the sensor resistance and voltage with a multimeter. The post-evaporator sensor is typically a thermistor — resistance decreases as temperature rises. Compare your readings against manufacturer specifications. A reading near zero ohms or zero volts suggests a direct short to ground.
5. Check the ground circuit feeding the sensor and its module. Use a wiring diagram to locate the ground point and verify it reads less than 1 ohm to chassis ground. A poor ground can create phantom short conditions.
6. Clear the code, start the vehicle, enable the A/C under the conditions from your freeze frame, and see if B1947 returns. If it does, you have an active fault. If not, the issue was intermittent.

Repair Options and Costs

Once you've identified the failed component, repair costs vary by what needs replacing. Parts pricing below reflects average ranges for quality OE-style replacement parts in USD.

• Replace post-evaporator temperature sensor: $40–$120 (part) + $50–$100 labor (0.5–1.0 hour)
• Repair damaged sensor wiring harness: $50–$150 (labor and materials)
• Replace sensor electrical connector: $30–$80 (part) + $50–$100 labor
• Replace body control module (rare): $300–$800 (part and programming)

Total repair cost for B1947 typically falls between $90 and $250 if the sensor itself is the problem — the most common scenario. Module replacement pushes the total toward $500–$900 when required. Always verify the actual failure point before purchasing a module, as BCM issues are uncommon for this specific code.

Driving Safety Verdict

B1947 carries a short severity rating — you can safely continue driving. This fault affects cabin comfort and defrost effectiveness, not engine operation or vehicle control. However, a malfunctioning A/C system can leave windows fogged in humid or cold conditions, reducing visibility. If you notice fogging issues or operate in climates where A/C defogging matters, schedule the repair sooner rather than later. The post-evaporator sensor itself is inexpensive, and diagnosis is straightforward for any shop with a multimeter and a wiring diagram.

Related OBD2 Codes

• B1900: Driver Side Airbag Fault
• B1901: Air Bag Crash Sensor #1 Feed/Return Circuit Short To Ground
• B1902: Air Bag Crash Sensor #1 Ground Circuit Failure
• B1903: Air Bag Crash Sensor #1 Ground Circuit Short To Battery
• B1904: Air Bag Crash Sensor #2 Feed/Return Circuit Failure
• [B1905: Air Bag Crash Sensor #2 Feed/Return Circuit Short To Battery](

The B1947 OBD2 fault code relates to the Climate Control A/C Post Evaporator Sensor circuit. When the circuit circuit failure, the module cannot properly monitor or control this body system.

At AIscanAuto, we help drivers quickly identify OBD2 trouble codes, understand their root causes, and find the right fix.

Symptoms

• Climate control not responding
• A/C pressure issues
• Temperature not adjusting
• Possible blower motor issues

Common Causes

• Faulty component — internal damage or wear affecting Climate Control A/C Post Evaporator Sensor
• Wiring issues — broken, corroded, or chafed wires in the circuit
• Connector problems — loose, oxidized, or moisture-damaged pins
• a general circuit failure is detected — can result from wiring faults, connector issues, or component failure
• Module input failure — rare, but the control module input stage may be defective

Step-by-Step Diagnosis

1. Scan with OBD2 tool — Confirm B1947 is active. Check for additional DTCs.
2. Visual inspection — Examine the Climate Control A/C Post Evaporator Sensor wiring and connector for corrosion or damage.
3. Check voltage and ground — Use a multimeter to verify proper reference voltage.
4. Test component — Compare readings to factory specs. A stuck or erratic signal confirms failure.
5. Check for shorts/opens — Perform continuity tests on the wiring between the component and control module.

Repair & Solutions

• If the component is defective, replace the Climate Control A/C Post Evaporator Sensor with an OEM or quality aftermarket part.
• Repair any damaged wiring or connectors using proper methods.
• Clear the DTC with an OBD2 scanner and test drive to verify the code does not return.
• If the code persists after component replacement, inspect the control module connector.

Related Codes

• B1944 — Air Bag Crash Sensor #2 Feed/Return Circuit Failure
• B1945 — Air Bag Crash Sensor #2 Feed/Return Circuit Short To Battery
• B1946 — Climate Control A/C Post Evaporator Sensor Circuit Failure