The P0339 trouble code is a diagnostic trouble code (DTC) that your vehicle’s onboard computer system, often referred to as the Engine Control Unit (ECU) or Powertrain Control Module (PCM), may log. Specifically, it relates to the crankshaft position sensor, a crucial component in your engine’s operation. When the PCM detects an irregular signal from this sensor, specifically an intermittent signal on the “A” circuit, the P0339 code is triggered, and your check engine light will likely illuminate.
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Decoding the P0339 Code: Crankshaft Position Sensor ‘A’ Circuit Intermittent
The P0339 code is formally defined as “Crankshaft Position Sensor ‘A’ Circuit Intermittent.” This means the PCM has detected a problem with the signal coming from crankshaft position sensor “A.” The term “intermittent” is key here, indicating that the issue isn’t constant but rather occurring sporadically. The crankshaft position sensor’s job is to monitor the position and rotational speed of the crankshaft. This information is vital for the PCM to accurately control fuel injection and ignition timing, ensuring smooth and efficient engine operation.
When the PCM registers a P0339 code, it signifies that the voltage signal from the crankshaft position sensor is fluctuating or dropping out unexpectedly. This can happen for brief periods, making diagnosis challenging as the fault may not be present continuously. Typically, the PCM will need to detect the fault multiple times over several drive cycles before setting the P0339 code and turning on the check engine light. However, a pending code may be stored even before the light comes on, indicating an early stage of the problem.
Common Causes of a P0339 OBDII Code
Several factors can lead to an intermittent signal from the crankshaft position sensor and the subsequent P0339 code. Pinpointing the exact cause requires a systematic diagnostic approach. Here are the most frequent culprits:
- Faulty Crankshaft Position Sensor: The sensor itself may be failing due to age, wear, or internal damage. An intermittent fault within the sensor can cause signal disruptions.
- Wiring Harness Issues: Damage to the wiring harness connected to the crankshaft position sensor is a very common cause. This can include:
- Chafing or Fraying: Wires can rub against engine components, leading to damaged insulation and intermittent shorts or open circuits.
- Corrosion: Exposure to moisture, road salt, or engine fluids can corrode wiring and connectors, disrupting signal flow.
- Engine Oil Contamination: Oil leaks near the sensor or wiring can degrade wire insulation and connector seals, causing intermittent electrical problems.
- Connector Problems: Loose, corroded, or damaged connectors at the crankshaft position sensor or the PCM can create intermittent signal loss.
- Reluctor Ring Damage: The crankshaft position sensor reads teeth or notches on a reluctor ring (also known as a tone wheel) attached to the crankshaft. If this ring is damaged, bent, or has missing teeth, it can produce an erratic signal.
- Timing Belt/Chain Issues: In rare cases, a severely worn or damaged timing belt or chain could potentially interfere with the crankshaft position sensor or reluctor ring, although this is less common for a P0339 code specifically.
- PCM Failure (Rare): While less likely, a fault within the PCM itself could, in rare instances, misinterpret the crankshaft position sensor signal or falsely set the P0339 code. This is usually diagnosed after ruling out all other possibilities.
Symptoms Indicating a P0339 Trouble Code
The symptoms associated with a P0339 code can vary widely in severity. In some cases, you might not notice any symptoms at all, while in others, the drivability of your vehicle can be significantly affected. Here’s a range of potential symptoms:
- Check Engine Light Illumination: This is the most consistent symptom. The malfunction indicator lamp (MIL), or check engine light, will turn on to alert you to a problem.
- No Noticeable Symptoms: In the early stages or with very intermittent faults, you might not experience any changes in how your car drives. However, the underlying issue still needs to be addressed.
- Reduced Engine Performance: The PCM relies on accurate crankshaft position sensor data for optimal engine management. An intermittent signal can lead to:
- Rough Idling: The engine may idle unevenly or feel shaky.
- Engine Misfires: You may experience stumbles or jerks during acceleration or at steady speeds.
- Poor Acceleration: The engine may feel sluggish or lack power when you try to accelerate.
- Reduced Fuel Economy: Inefficient engine operation due to inaccurate sensor readings can lead to decreased fuel mileage.
- Hard Starting or No Start Condition: In more severe cases, especially if the crankshaft position sensor signal is frequently lost, the engine may become difficult to start or fail to start altogether. This is because the PCM needs the crankshaft position signal to initiate fuel and ignition sequences.
Diagnosing the P0339 Code: A Mechanic’s Approach
A proper diagnosis is crucial to accurately fix a P0339 code. Here’s how a qualified mechanic would typically approach the problem:
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Initial Scan and Code Verification: The first step is to connect an OBD-II scanner to the vehicle’s diagnostic port. This allows the mechanic to read all stored DTCs, including the P0339 code and any related codes. The codes are noted, and then cleared.
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Test Drive and Code Re-Verification: If possible and safe, a test drive is conducted to see if the P0339 code and symptoms reappear. This helps confirm that the issue is still present and not just a fleeting anomaly.
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Visual Inspection of Wiring and Connectors: A thorough visual inspection is critical. The mechanic will carefully examine:
- Crankshaft Position Sensor Wiring Harness: Looking for signs of damage, chafing, melting, or oil contamination along the entire harness.
- Connectors: Checking for loose connections, corrosion, bent pins, and damage at both the sensor and PCM connectors.
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Crankshaft Position Sensor Testing: If wiring and connectors appear to be in good condition, the crankshaft position sensor itself needs to be tested. This can involve:
- Resistance Testing: Using a multimeter to measure the sensor’s resistance and compare it to manufacturer specifications. An out-of-range reading indicates a faulty sensor.
- Signal Testing (Oscilloscope or Scanner): Using an oscilloscope or advanced scan tool to monitor the sensor’s signal output while the engine is running or being cranked. This can reveal intermittent signal dropouts or abnormalities that are not detectable with simple resistance testing. Sometimes this test requires removing the sensor for better access or specific testing procedures.
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Reluctor Ring Inspection (If Accessible): In some cases, if wiring and sensor tests are inconclusive, and reluctor ring damage is suspected, the mechanic might need to access and visually inspect the reluctor ring for damage or debris. This may require removing other components for access.
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PCM Testing (Last Resort): Only after thoroughly investigating all other potential causes would a mechanic suspect PCM failure. PCM testing is complex and usually involves specialized tools and procedures. It’s typically performed as a last resort.
Common Diagnostic Mistakes to Avoid
A frequent error in diagnosing P0339 is immediately assuming the crankshaft position sensor is faulty and replacing it without proper investigation. While the sensor can fail, wiring and connector issues are often the real underlying problem. Oil contamination of the wiring harness is a particularly common culprit and easily overlooked. A complete and methodical diagnosis, as outlined above, is essential to avoid unnecessary parts replacements and ensure the root cause is correctly addressed.
Severity of the P0339 Code
The P0339 code should be considered serious, even if your vehicle seems to be driving normally. An intermittent crankshaft position sensor signal can become more frequent or turn into a complete signal loss at any time. This can lead to sudden engine stalling or a no-start condition, potentially leaving you stranded. Furthermore, if the underlying issue is wiring damage due to oil leaks, this problem will likely worsen over time. It’s recommended to have a P0339 code diagnosed and repaired promptly to prevent more significant problems and ensure vehicle reliability.
Repairs to Fix the P0339 Code
The necessary repairs for a P0339 code depend entirely on the identified root cause. Here are common repairs:
- Wiring Harness Repair or Replacement: This is frequently needed. It may involve:
- Repairing Damaged Wires: Splicing in new wire sections to replace frayed or broken wires.
- Replacing Connectors: Replacing corroded or damaged connectors.
- Complete Harness Replacement: In severe cases of widespread damage or oil contamination, replacing the entire crankshaft position sensor wiring harness section may be necessary.
- Crankshaft Position Sensor Replacement: If testing confirms the sensor itself is faulty, replacement is required.
- Reluctor Ring Repair or Replacement: If the reluctor ring is damaged, it will need to be repaired or replaced. This can sometimes be a more involved repair requiring crankshaft disassembly in certain vehicles.
- Oil Leak Repair: If oil leaks are contributing to wiring damage, addressing these leaks is crucial to prevent recurrence of the P0339 code and other related issues.
Important Considerations for P0339 Diagnosis and Repair
Because the P0339 code can have multiple underlying causes, a thorough and systematic diagnostic process is paramount. Simply replacing the crankshaft position sensor without investigating wiring and other potential issues is often ineffective and can lead to misdiagnosis and repeated repairs. A skilled technician will perform a comprehensive inspection and testing procedure to pinpoint the precise cause and implement the correct repair, saving you time, money, and frustration in the long run.
Do you need help diagnosing and fixing a P0339 code? Autel France’s network of expert mechanics are available to assist you. Contact us today for a quote and to schedule a diagnostic appointment.
