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

Note: The description for code B1947 may vary depending on the vehicle manufacturer. Always refer to OEM documentation for your specific model.

• Ford/Lincoln/Mercury: Climate Control A/C Post Evaporator Sensor Circuit Short To Ground
• Toyota/Lexus: Air Conditioning Evaporator Temperature Sensor Circuit Low Input
• GM: HVAC Post-Evaporator Temperature Sensor Circuit Low
• Chrysler: A/C Evaporator Temperature Sensor Circuit Short To Ground

Code Summary for B1947 #

DTC B1947 indicates that the vehicle’s climate control system has detected a short to ground in the circuit for the post-evaporator temperature sensor. This sensor, located just after the evaporator in the air conditioning (A/C) system, plays a key role in monitoring air temperature to prevent evaporator freezing and ensure optimal cabin comfort. When the circuit is shorted to ground, the system receives an abnormally low voltage reading, triggering a fault code and potentially affecting A/C performance. This condition is commonly flagged by the Body Control Module (BCM) or the HVAC control module. Prompt diagnosis is important to restore proper climate control function and avoid further system issues.

Common Symptoms for Code B1947 #

A short to ground in the post-evaporator sensor circuit can cause a range of noticeable climate control issues. Depending on the vehicle and climate control strategy, symptoms may be subtle or immediately obvious. Watch for these signs if B1947 is present:

• Erratic or non-functional A/C operation
• Cabin temperature not matching the set value
• A/C compressor cycling on and off rapidly, or not engaging at all
• Possible illumination of the A/C warning indicator or check engine light
• Unusual noises from the HVAC system
• Blower fan running at incorrect speeds

Most Likely Causes for B1947 #

The root cause of a B1947 code is usually an electrical fault affecting the sensor circuit, but it can also be related to component failure or wiring issues. Here are the most common culprits, listed in order of frequency:

1. Damaged or shorted wiring harness (especially where wires run near sharp metal or moving HVAC components)
2. Faulty post-evaporator temperature sensor (internal short, corrosion, or water ingress)
3. Loose or corroded electrical connectors (causing intermittent grounding)
4. Failed HVAC control module or BCM (rare, but possible if other codes are present)
5. Incorrect sensor installation or previous repair errors

Step-by-Step Diagnostic for B1947 #

A systematic approach helps you identify the true cause of B1947 and avoids unnecessary parts replacement. Here’s a proven process used by master technicians:

• 1. Confirm the code using a compatible OBD-II/EOBD scanner and clear any stored codes.
• 2. Inspect the wiring from the post-evaporator sensor to the control module. Look for damaged insulation, pinched wires, or signs of grounding.
• 3. Check connectors for corrosion, loose pins, or moisture. Reseat all connectors and ensure proper fit.
• 4. Test the sensor with a digital multimeter. Measure resistance across sensor terminals compared to OEM specs (typically several kilo-ohms at room temperature). Low or zero resistance may indicate a short.
• 5. Check ground paths to ensure the sensor’s circuit is not accidentally grounded elsewhere.
• 6. If wiring and sensor test fine, use scan tool data to monitor sensor readings with the system powered on. Look for unexpected values (e.g., -40°F or constant low reading).
• 7. As a last resort, test the HVAC control module or BCM (per OEM procedure) for internal faults.

Possible Repairs for B1947 #

Once the root cause is identified, repairs are generally straightforward and should target the failed component or connection. Here are the most common fixes linked to the causes above:

• Repair or replace damaged wiring harnesses and ensure wires are properly routed and insulated.
• Replace the post-evaporator temperature sensor if resistance readings are out of spec or sensor shows physical damage.
• Clean and secure electrical connectors to eliminate corrosion and ensure tight contact.
• Replace the HVAC control module or BCM only if confirmed faulty by diagnostic testing (rare).
• Correct any previous installation errors or improper repairs that could cause grounding issues.

Is It Safe to Drive with Code B1947? #

Limited: While code B1947 does not typically affect engine performance or basic vehicle safety, it can lead to loss of proper climate control and may prevent the A/C system from functioning correctly. This can be uncomfortable in hot weather and, in some cases, may affect defogging or demisting functions. Prolonged use with this code is not recommended, especially if you rely on A/C for safety or comfort.

Vehicles Most Commonly Affected by B1947 #

B1947 is most often reported on vehicles with automatic climate control systems and advanced HVAC diagnostics. Models where this code is more frequently encountered include:

• Ford (Fusion, Explorer, Taurus, Expedition, F-150 with auto A/C)
• Lincoln (MKX, Navigator, MKZ)
• Mercury (Milan, Mountaineer)
• Toyota (Avalon, Camry, Highlander with auto HVAC)
• Lexus (ES, RX, LS series)
• GM (Chevrolet Impala, Buick LaCrosse with digital climate control)

Common Mistakes & Best Practices for B1947 #

Misdiagnosis of B1947 often leads to wasted time and unnecessary parts replacement. Here are some pitfalls to avoid and tips for a successful repair:

• Replacing the sensor without checking wiring first — damaged harnesses are a frequent cause
• Overlooking connector corrosion, especially in vehicles exposed to moisture
• Forgetting to clear the code and verify the repair after work is done
• Skipping OEM wiring diagrams — always use the schematic for your exact model
• Testing sensor resistance at the module connector to rule out harness faults

Quick FAQ for Code B1947 #

Still have questions? Here are brief answers to the most common concerns:

• Q: Will B1947 damage my A/C system?
  A: Not directly, but it can cause the A/C to run improperly, potentially leading to secondary issues like evaporator icing or compressor overwork if ignored.
• Q: Can I clear the code and ignore it?
  A: Clearing the code without fixing the root cause will only temporarily remove the warning. The problem will return, and your climate control system will not function as designed.