Introduction:
The B1947 Diagnostic Trouble Code (DTC) indicates a fault in the climate control system, specifically a short to ground in the circuit for the A/C post-evaporator temperature sensor. This sensor plays a crucial role in regulating the air conditioning system, and a malfunction can lead to inefficient cooling, system shutdowns, or even damage to components. Understanding the causes, symptoms, and troubleshooting steps for this code is essential for effective diagnosis and repair.
Table: B1947 Climate Control A/C Post Evaporator Sensor Circuit Short To Ground
| Topic | Description | Possible Causes |
|---|---|---|
| Definition of B1947 | Diagnostic Trouble Code indicating a short circuit to ground in the A/C post-evaporator temperature sensor circuit. | Damaged wiring harness, faulty sensor, shorted connector, or a problem within the climate control module (HVAC control module). |
| Sensor Function | Measures the temperature of the air exiting the evaporator core. | Prevents evaporator core freeze-up, regulates compressor operation, and provides data for accurate temperature control inside the vehicle. |
| Common Symptoms | Inefficient A/C cooling, A/C system shutting down intermittently, no A/C operation, DTC B1947 present. | Warm air blowing from vents, A/C compressor cycling rapidly, A/C compressor not engaging, engine overheating (in some cases), and potential issues with other climate control features. |
| Wiring Diagram Basics | Typically involves a 5V reference signal wire, a ground wire, and a signal wire to the HVAC control module. | Visual inspection is crucial. Trace the wires from the sensor back to the HVAC control module, looking for damage, corrosion, or shorts to ground. Use a multimeter to test continuity. |
| Testing the Sensor | Use a multimeter to measure resistance across the sensor terminals and compare it to the manufacturer's specifications. | Disconnect the sensor and check for shorts to ground on the signal wire using a multimeter. A reading of 0 ohms indicates a short. |
| HVAC Control Module Role | Receives sensor data and controls the A/C system. | Internal failure within the module can cause false sensor readings or prevent the module from correctly interpreting the sensor data. |
| Scan Tool Diagnosis | Reads DTCs, monitors sensor data, and performs actuator tests. | Use a scan tool to monitor the post-evaporator temperature sensor reading in real-time. Compare the reading to ambient temperature. Also, use the scan tool to actuate A/C components. |
| Troubleshooting Steps | Visual inspection, wiring checks, sensor testing, connector inspection, HVAC control module testing. | Start with the simplest and most accessible components. Document each step of the troubleshooting process. Consult the vehicle's service manual for specific procedures. |
| Repair Solutions | Wiring repair, sensor replacement, connector repair/replacement, HVAC control module replacement/reprogramming. | Ensure the replacement parts are compatible with the vehicle. Clear the DTC after making repairs and retest the system. |
| Preventive Measures | Regular A/C system maintenance, protect wiring from damage, avoid harsh chemicals near electrical components. | Routine inspections of A/C system components can identify potential problems before they escalate. Properly routing and securing wiring can prevent chafing and damage. |
| Related DTCs | B1946 (Open Circuit), other A/C system codes. | These codes can provide additional clues about the nature of the problem. |
| Specific Vehicle Considerations | Different vehicle makes and models may have slightly different wiring configurations and sensor locations. | Refer to the vehicle's service manual or wiring diagrams for specific information. |
| Electrical Safety | Disconnect the battery before working on electrical components. | Use appropriate safety gear, such as gloves and eye protection. Be aware of the potential for electrical shock. |
Detailed Explanations:
Definition of B1947:
The B1947 code is a diagnostic trouble code (DTC) that specifically points to a short circuit to ground within the circuit that connects the A/C post-evaporator temperature sensor to the vehicle's climate control system. This means that the electrical signal from the sensor is inadvertently finding an unintended path to ground, disrupting the normal operation of the circuit. This short circuit causes the control module to receive an incorrect or no signal from the sensor.
Sensor Function:
The A/C post-evaporator temperature sensor is a thermistor, a resistor whose resistance changes with temperature. It is strategically placed after the evaporator core within the HVAC system. Its primary function is to measure the temperature of the air as it exits the evaporator. This temperature reading is vital for preventing the evaporator core from freezing up, which can damage the system and restrict airflow. The sensor's data is also used to regulate the compressor operation and accurately control the temperature inside the vehicle's cabin.
Common Symptoms:
When the B1947 code is present, several symptoms may manifest. The most common is inefficient A/C cooling, where the air conditioning system struggles to produce cold air. In some cases, the A/C system may shut down intermittently or fail to operate altogether. Other symptoms can include warm air blowing from the vents, rapid cycling of the A/C compressor (turning on and off frequently), the A/C compressor not engaging at all, and, in rare instances, even engine overheating. The presence of the DTC B1947 itself is a key symptom.
Wiring Diagram Basics:
Understanding the wiring of the post-evaporator temperature sensor circuit is crucial for troubleshooting. Typically, the circuit includes three wires: a 5V reference signal wire that provides a constant voltage to the sensor, a ground wire that provides a return path for the electrical current, and a signal wire that carries the temperature data from the sensor back to the HVAC control module. A short to ground occurs when the signal wire makes unintended contact with the vehicle's chassis or another grounded component. Visual inspection of the wiring harness is paramount; look for any signs of damage, corrosion, or chafing. Use a multimeter to test the continuity of each wire and ensure there are no shorts to ground.
Testing the Sensor:
To test the sensor itself, disconnect it from the wiring harness. Use a multimeter set to measure resistance (Ohms). Connect the multimeter leads to the sensor terminals and compare the resistance reading to the manufacturer's specifications, which can be found in the vehicle's service manual. If the resistance reading is significantly different from the specified range, the sensor is likely faulty and needs replacement. To check for a short to ground, disconnect the sensor and measure the resistance between the signal wire connector and a known good ground point on the vehicle's chassis. A reading of 0 ohms indicates a short circuit.
HVAC Control Module Role:
The HVAC (Heating, Ventilation, and Air Conditioning) control module is the brain of the climate control system. It receives the temperature data from the post-evaporator sensor and uses this information, along with data from other sensors, to regulate the A/C system's operation. The control module adjusts the compressor clutch engagement, blower motor speed, and blend door position to maintain the desired cabin temperature. An internal failure within the HVAC control module can cause false sensor readings, prevent the module from correctly interpreting the sensor data, or even cause the B1947 code to be set erroneously.
Scan Tool Diagnosis:
A scan tool is an invaluable tool for diagnosing A/C system problems. It allows you to read DTCs stored in the vehicle's computer, including the B1947 code. More importantly, it allows you to monitor the post-evaporator temperature sensor reading in real-time. Compare the sensor reading to the ambient temperature. If the sensor reading is consistently inaccurate or displays illogical values, it can point to a sensor fault or a wiring problem. A scan tool can also be used to perform actuator tests, such as engaging and disengaging the A/C compressor clutch, to verify the system's functionality.
Troubleshooting Steps:
A systematic approach to troubleshooting is essential. Start with a thorough visual inspection of the wiring harness, connectors, and the sensor itself. Look for any signs of damage, corrosion, or loose connections. Next, perform wiring checks using a multimeter to test for continuity and shorts to ground. Test the sensor's resistance and compare it to the manufacturer's specifications. Inspect the connectors for corrosion or damaged terminals. Finally, if all other components check out, suspect the HVAC control module. Consult the vehicle's service manual for specific troubleshooting procedures and wiring diagrams.
Repair Solutions:
The repair solution will depend on the root cause of the problem. If the wiring is damaged, repair or replace the affected section of the harness. If the sensor is faulty, replace it with a new one. If a connector is corroded or damaged, clean or replace it. If the HVAC control module is the culprit, it may need to be replaced or reprogrammed. Ensure that all replacement parts are compatible with the vehicle. After making repairs, clear the DTC using a scan tool and retest the system to verify that the problem has been resolved.
Preventive Measures:
Preventing A/C system problems is always better than fixing them. Regular A/C system maintenance, including checking refrigerant levels and inspecting components for leaks or damage, can help prevent future issues. Protect wiring from damage by ensuring it is properly routed and secured. Avoid using harsh chemicals near electrical components, as they can corrode wiring and connectors. Routine inspections of A/C system components can identify potential problems before they escalate and trigger DTCs like B1947.
Related DTCs:
While B1947 specifically indicates a short to ground in the post-evaporator sensor circuit, other related DTCs may also be present. For example, B1946 indicates an open circuit in the same sensor circuit. Other A/C system codes, such as those related to the compressor, refrigerant pressure, or other temperature sensors, can provide additional clues about the nature of the problem and help narrow down the cause.
Specific Vehicle Considerations:
It's crucial to remember that different vehicle makes and models may have slightly different wiring configurations and sensor locations for the A/C post-evaporator temperature sensor. The sensor's location may vary depending on the vehicle's design. Always refer to the vehicle's service manual or wiring diagrams for specific information about the A/C system in the particular vehicle you are working on.
Electrical Safety:
Working on electrical systems can be dangerous. Always disconnect the battery before working on any electrical components to prevent accidental shocks or damage to the vehicle's electrical system. Use appropriate safety gear, such as gloves and eye protection. Be aware of the potential for electrical shock and take necessary precautions to avoid injury.
Frequently Asked Questions:
What does the B1947 code mean? It means there's a short to ground in the A/C post-evaporator temperature sensor circuit, disrupting the signal.
Can a bad sensor cause the A/C to stop working? Yes, a faulty sensor can provide incorrect data, leading to the A/C system shutting down or malfunctioning.
How do I check for a short to ground? Use a multimeter to measure the resistance between the signal wire and a known ground point; a reading of 0 ohms indicates a short.
Is it safe to drive with a B1947 code? While generally safe, the A/C system might not function correctly, and prolonged issues can potentially damage other components.
Can I fix this myself, or do I need a mechanic? Depending on your mechanical skills, you might be able to diagnose and fix it; however, professional help is recommended for complex electrical issues.
Conclusion:
The B1947 DTC indicates a short to ground in the A/C post-evaporator temperature sensor circuit, leading to potential A/C system malfunctions. Proper diagnosis and repair, following a systematic approach, are crucial for restoring the system's functionality and preventing further damage.