The P1639 diagnostic trouble code (DTC) indicates a problem with the 5-volt reference circuit number 2 in a vehicle's engine control system. This circuit is crucial for supplying a stable voltage to various sensors, allowing the engine control module (ECM) or powertrain control module (PCM) to accurately interpret sensor readings and control engine functions. A malfunctioning 5-volt reference circuit can lead to inaccurate sensor data, resulting in poor engine performance, reduced fuel efficiency, and potentially even engine damage.
Comprehensive Table of P1639 Information
| Category | Description | Possible Causes |
|---|---|---|
| Definition | Indicates a fault within the 5-volt reference circuit number 2. This circuit provides a consistent 5-volt power supply to various sensors, enabling them to function correctly. | Short circuit to ground in the 5-volt reference circuit, short circuit to voltage in the 5-volt reference circuit, open circuit in the 5-volt reference circuit, faulty sensor(s) drawing excessive current, faulty PCM/ECM. |
| Affected Sensors | Varies depending on vehicle manufacturer and specific circuit configuration. Common sensors include: Throttle Position Sensor (TPS), Manifold Absolute Pressure (MAP) sensor, Camshaft Position Sensor (CMP), Crankshaft Position Sensor (CKP), Fuel Rail Pressure Sensor (FRP), Accelerator Pedal Position Sensor (APP). | Sensor failure, wiring harness damage, connector corrosion, PCM/ECM failure. |
| Symptoms | Check Engine Light (CEL) illuminated, poor engine performance (hesitation, stalling, rough idle), reduced fuel economy, transmission problems (erratic shifting), failure to start, sensor readings outside of expected range (observable with a scan tool), ABS or Traction Control issues (in some cases). | Sensor failure, wiring harness damage, connector corrosion, PCM/ECM failure. |
| Diagnostic Steps | 1. Verify the presence of a stable 5-volt reference voltage at the affected sensors using a multimeter. 2. Inspect wiring harness and connectors for damage, corrosion, or loose connections. 3. Check for shorts to ground or voltage in the 5-volt reference circuit. 4. Disconnect sensors one at a time to isolate a faulty sensor drawing excessive current. 5. Test sensor resistance and voltage output. 6. Perform a PCM/ECM self-test. 7. Consult vehicle-specific wiring diagrams. | Faulty wiring harness, faulty sensor, faulty PCM/ECM, incorrect diagnostic procedure. |
| Potential Solutions | Repair or replace damaged wiring harness and connectors, replace faulty sensor(s), replace faulty PCM/ECM (requires programming), repair short circuits to ground or voltage, clean corroded connections. | Incorrect repair, ignoring underlying cause, improper PCM/ECM programming. |
| Severity | Moderate to High. A malfunctioning 5-volt reference circuit can significantly impact engine performance and potentially lead to further damage if not addressed promptly. | N/A |
| Related DTCs | P0641 (5-Volt Reference 1 Circuit), P0697 (5-Volt Reference 3 Circuit), other sensor-specific DTCs related to sensors receiving the 5-volt reference. | N/A |
| Tools Required for Diagnosis | Multimeter, scan tool (capable of reading live sensor data), wiring diagrams for the specific vehicle, circuit tester, terminal tools (for connector repair), wire strippers, crimpers. | N/A |
| Circuit Location | The exact location of the 5-volt reference circuit and its associated components varies depending on the vehicle manufacturer and model. Consult vehicle-specific wiring diagrams for accurate identification. | N/A |
Detailed Explanations
Definition: The P1639 code indicates a problem with the 5-volt reference circuit number 2. The ECM/PCM uses this circuit to provide a stable 5-volt power supply to various sensors, allowing them to function correctly and send accurate data back to the computer. A fault in this circuit means the sensors aren't receiving the correct voltage, leading to inaccurate readings.
Affected Sensors: The sensors affected by the P1639 code depend heavily on the vehicle make and model and how the manufacturer designed the 5-volt reference circuits. Common sensors powered by a 5V reference include the Throttle Position Sensor (TPS), Manifold Absolute Pressure (MAP) sensor, Camshaft Position Sensor (CMP), Crankshaft Position Sensor (CKP), Fuel Rail Pressure Sensor (FRP), and Accelerator Pedal Position Sensor (APP). Consult vehicle-specific wiring diagrams to identify exactly which sensors are on the affected circuit.
Symptoms: The symptoms of a P1639 code can range from minor to severe, depending on which sensors are affected and the nature of the fault. Common symptoms include the Check Engine Light (CEL) illuminating, poor engine performance such as hesitation, stalling, or rough idling, reduced fuel economy, transmission problems like erratic shifting, and even a failure to start. A scan tool can also reveal sensor readings that are outside of their expected range. In some cases, ABS or Traction Control issues can also arise.
Diagnostic Steps: Diagnosing a P1639 code requires a systematic approach. Start by verifying the presence of a stable 5-volt reference voltage at the affected sensors using a multimeter. Next, carefully inspect the wiring harness and connectors associated with the circuit for any signs of damage, corrosion, or loose connections. Check for shorts to ground or voltage within the 5-volt reference circuit. Try disconnecting sensors one at a time to see if isolating a faulty sensor drawing excessive current resolves the issue. Test the resistance and voltage output of the sensors themselves. Perform a PCM/ECM self-test to rule out internal issues. Finally, consult vehicle-specific wiring diagrams to understand the circuit layout and component locations.
Potential Solutions: The solutions for a P1639 code depend on the underlying cause. Repairing or replacing damaged wiring harness and connectors is often necessary. Faulty sensors should be replaced. If the PCM/ECM is found to be faulty, it will need to be replaced and programmed. Repairing short circuits to ground or voltage is also crucial. Cleaning corroded connections can also resolve the issue.
Severity: The severity of a P1639 code is generally considered moderate to high. A malfunctioning 5-volt reference circuit can significantly impact engine performance, leading to driveability issues and potentially causing further damage to other components if not addressed promptly.
Related DTCs: The P1639 code is often related to other diagnostic trouble codes. P0641 (5-Volt Reference 1 Circuit) and P0697 (5-Volt Reference 3 Circuit) indicate similar issues with other 5-volt reference circuits. Additionally, sensor-specific DTCs related to sensors that receive the 5-volt reference, such as codes for the TPS, MAP sensor, or CMP sensor, may also be present.
Tools Required for Diagnosis: Diagnosing a P1639 code effectively requires a few specialized tools. A multimeter is essential for measuring voltage and resistance. A scan tool capable of reading live sensor data is necessary for monitoring sensor outputs. Vehicle-specific wiring diagrams are crucial for understanding the circuit layout. A circuit tester can help identify shorts and open circuits. Terminal tools are needed for connector repair, and wire strippers and crimpers are required for wiring repairs.
Circuit Location: The location of the 5-volt reference circuit number 2 and its associated components varies significantly depending on the vehicle manufacturer and model. The best way to determine the exact location is to consult vehicle-specific wiring diagrams. These diagrams will show the routing of the wiring harness, the location of connectors, and the specific sensors that are powered by the circuit.
Frequently Asked Questions
What does the P1639 code mean? The P1639 code indicates a problem with the 5-volt reference circuit number 2 in your vehicle's engine control system. This circuit provides power to several sensors, and a fault can cause inaccurate readings.
What are the symptoms of a P1639 code? Symptoms can include a check engine light, poor engine performance (stalling, hesitation), reduced fuel economy, and transmission problems.
Can I fix a P1639 code myself? While some repairs, like cleaning connections, might be possible for a DIYer, diagnosing and repairing electrical issues often requires specialized tools and knowledge. It's generally recommended to consult a qualified mechanic.
What is a 5-volt reference circuit? A 5-volt reference circuit provides a stable 5-volt power supply to various sensors, allowing the engine control module (ECM) to accurately interpret sensor readings.
What sensors are usually on the 5-volt reference circuit? Common sensors include the Throttle Position Sensor (TPS), Manifold Absolute Pressure (MAP) sensor, and Camshaft Position Sensor (CMP), but it varies by vehicle. Consult your vehicle's wiring diagram for specifics.
Conclusion
The P1639 diagnostic trouble code signifies a fault within the 5-volt reference circuit number 2, impacting sensor functionality and potentially causing various engine performance issues. Accurate diagnosis and repair, often involving wiring harness inspection, sensor testing, and PCM/ECM evaluation, are crucial for resolving this code and restoring optimal vehicle operation.