As a content creator for keyfobprog.com and an experienced auto repair specialist, I’m here to break down the P0671 trouble code. This code is a common issue in diesel vehicles, and understanding it is the first step to getting your engine running smoothly again. The P0671 code specifically points to a problem in the Cylinder #1 Glow Plug Circuit. Let’s dive into what this means, what the symptoms are, and how you can diagnose and fix it.
Decoding the P0671 Trouble Code: Cylinder #1 Glow Plug Circuit Malfunction
The P0671 code is a generic powertrain code (OBD-II), which means it can appear in most diesel vehicles manufactured from 1996 onwards. However, specific troubleshooting steps might vary slightly depending on your vehicle’s make and model.
This code indicates a malfunction within the circuit that controls the glow plug in cylinder #1. Glow plugs are essential components in diesel engines, especially in cold weather. Unlike gasoline engines, diesels rely on intense heat generated by compression to ignite fuel. When the engine is cold, the cylinder head can absorb much of this heat, making ignition difficult. This is where glow plugs come in.
Understanding Glow Plugs:
Glow plugs are small, pencil-shaped heaters located in the cylinder head, very close to the combustion chamber. When your diesel engine is cold, the engine control module (ECM) or powertrain control module (PCM) activates the glow plugs for a few seconds before and during startup. They heat the air in the combustion chamber, ensuring a sufficiently high temperature for the diesel fuel to ignite.
The Glow Plug Circuit Explained:
The glow plug system typically includes:
- Glow Plugs: The heating elements themselves.
- Glow Plug Relay/Module: This component controls the power supply to the glow plugs, as they require a significant amount of electricity. The module is often integrated into the PCM but can also be a separate unit.
- Wiring and Connectors: These carry the electrical current to the glow plugs.
- Temperature Sensors: These sensors (like oil and transmission sensors) inform the PCM about engine temperature, helping it decide when to activate the glow plugs.
When the PCM detects a fault in the Cylinder #1 glow plug circuit, it sets the P0671 code. This means there’s an issue preventing the glow plug in cylinder #1 from functioning correctly.
A typical diesel engine glow plug:
Alt text: Close-up of a diesel engine glow plug, highlighting the heating element at the tip, used in automotive repair articles for P0671 code diagnostics.
Recognizing the Symptoms of a P0671 Code
While a single faulty glow plug might not cause dramatic symptoms in milder weather, you’ll likely notice issues, especially in cold conditions. The most obvious sign is the check engine light illuminating on your dashboard. Beyond that, here are common symptoms associated with the P0671 code:
- Check Engine Light: This is usually the first and most consistent symptom.
- Hard Starting or No Start in Cold Weather: This is the most noticeable performance issue. Without a functioning glow plug in cylinder #1, the engine will struggle to start when cold.
- Engine Misfire: A cold cylinder head can cause the engine to misfire, particularly when cold, leading to rough idling or hesitation.
- Lack of Power When Cold: The engine might feel sluggish and underpowered until it warms up to operating temperature.
- Hesitation During Acceleration: Misfires and uneven combustion can cause hesitation when you try to accelerate.
- Extended Preheat Time (if applicable): Some vehicles have a preheat light that indicates when glow plugs are active. If this light stays on for an extended period or doesn’t turn off, it could be related to a glow plug circuit issue.
It’s important to note that if you also have a P0670 code (Glow Plug Control Circuit Malfunction), you should address the P0670 code first, as it could be the root cause of the P0671.
Pinpointing the Potential Causes of a P0671 Code
Several factors can trigger the P0671 code. Here’s a breakdown of the most common culprits:
- Faulty Cylinder #1 Glow Plug: The glow plug itself might be burned out, damaged, or have failed internally. This is the most frequent cause.
- Open or Shorted Glow Plug Circuit: There could be a break (open circuit) or a short circuit in the wiring leading to the cylinder #1 glow plug. This can be due to damaged wires, corrosion, or rodent damage.
- Damaged Wiring Connector: The electrical connector at the glow plug or elsewhere in the circuit could be corroded, loose, or damaged, causing a poor connection.
- Faulty Glow Plug Control Module: Although less common, the glow plug control module or the PCM itself could be malfunctioning and incorrectly diagnosing or controlling the glow plug circuit.
Step-by-Step Diagnostic Procedures and Solutions for P0671
Diagnosing a P0671 code requires a systematic approach. Here’s a step-by-step guide you can follow:
Tools You’ll Need:
- Digital Volt Ohm Meter (DVOM)
- OBD-II Code Scanner
Step 1: Initial Checks and Code Scan
- Visually inspect the wiring and connectors leading to the cylinder #1 glow plug. Look for any signs of damage, corrosion, or looseness.
- Use an OBD-II scanner to confirm the P0671 code is present and check for any other related codes, especially P0670. Clear the codes after noting them down.
Step 2: Glow Plug Resistance Test
- Locate the cylinder #1 glow plug. Refer to your vehicle’s service manual for the exact location.
- Disconnect the electrical connector from the glow plug.
- Set your DVOM to the Ohms setting (resistance measurement).
- Place the red lead of the DVOM on the terminal of the glow plug and the black lead on a good ground point on the engine (unpainted metal surface).
- Compare the resistance reading to the specifications in your vehicle’s service manual. Generally, a good glow plug will read between 0.5 to 2.0 ohms. A reading outside this range (too high or infinite resistance) indicates a faulty glow plug.
- If the resistance is out of spec, replace the cylinder #1 glow plug.
Step 3: Wiring Circuit Resistance Test
- Locate the glow plug relay or buss bar. This is usually near the valve cover and has a heavy gauge wire connected to it.
- Identify the wire leading to the cylinder #1 glow plug on the buss bar.
- Disconnect the wire from the buss bar (or relay if applicable).
- Keep the connector disconnected from the glow plug itself (from Step 2).
- Using your DVOM set to Ohms, place the red lead on the connector of the wire you disconnected from the buss bar (relay end) and the black lead on the connector of the wire you disconnected from the glow plug (glow plug end).
- Again, the resistance should be within 0.5 to 2.0 ohms. Higher resistance indicates excessive resistance in the wire, possibly due to corrosion or damage.
- If the resistance is high, inspect the wire for damage and replace the wire lead to the glow plug. Note that these leads are often fusible links.
Step 4: Visual Inspection of Wiring and Connectors (Detailed)
- Carefully examine the entire length of the wiring for the cylinder #1 glow plug circuit. Look for:
- Cracks or breaks in the insulation.
- Signs of melting or burning.
- Corrosion at connectors.
- Loose or damaged connectors.
- Rodent damage (chewed wires).
- Repair or replace any damaged wiring or connectors as needed.
Step 5: Clear Codes and Retest
- Reconnect all wiring connectors securely.
- Use your OBD-II scanner to clear the P0671 code.
- Start the engine and check if the code returns.
- If the code does not return and the engine starts and runs normally, the issue is resolved.
If the P0671 code persists after these steps, it is possible, though less likely, that the glow plug control module or the PCM itself is faulty. Further diagnostics might require specialized tools and expertise. In such cases, it’s best to consult a qualified mechanic.
Further Resources for P0671 Code Troubleshooting
For additional information and community support, you can explore these resources:
- Online Automotive Forums: Websites like keyfobprog.com’s free car repair forums are excellent places to discuss your specific issue with other car owners and mechanics.
- Vehicle-Specific Forums: Search for forums dedicated to your vehicle’s make and model. You might find threads discussing P0671 codes in similar vehicles.
- YouTube Videos: Many helpful videos demonstrate glow plug testing and replacement procedures.
Still Need Help with P0671 Code?
If you’re still struggling to diagnose and fix the P0671 code, don’t hesitate to post your question in our FREE car repair forums. Our community of experienced mechanics and car enthusiasts is ready to assist you.
Disclaimer: This information is for informational purposes only and should not be considered professional repair advice. We are not responsible for any actions you take on your vehicle based on this information. Always consult a qualified mechanic for complex repairs.
