P0671 Cylinder 1 Glow Plug Circuit Code

OBD-II Trouble Code - P0671 - Data Sheet

P0671 - Cylinder #1 glow plug circuit

What does trouble code P0671 mean?

This Diagnostic Trouble Code (DTC) is a generic transmission code. It is considered universal as it applies to all makes and models of vehicles (1996 and newer), although the specific repair steps may differ slightly depending on the model.

This code refers to a device used by diesels to heat the cylinder head for a few seconds when trying to start a cold engine, called a glow plug. Diesel relies entirely on instant, high levels of compression heat to spontaneously ignite the fuel. The glow plug in cylinder # 1 is out of order.

When a diesel engine is cold, the extremely high air temperature caused by piston lift and air compression is quickly lost due to heat transfer to the cold cylinder head. The solution is a pencil-shaped heater known as a "glow plug".

The glow plug is installed in the cylinder head very close to the point that initiates combustion, or "hot spot". This can be the main chamber or the pre-chambers. When the ECM determines that the engine is cold using the oil and transmission sensors, it decides to assist the engine with starting with the glow plugs.

Typical Diesel Engine Glow Plug:

It grounds the glow plug timer module, which in turn grounds the glow plug relay, which supplies power to the glow plugs. The module supplies power to the glow plugs. This module is usually built into the engine control computer, although it will be separate in cars.

Activating too long will cause the glow plugs to melt as they generate heat through high resistance and are red-hot when activated. This intense heat is quickly transferred to the cylinder head, allowing the combustion heat to retain its heat for the fraction of a second it takes to ignite the incoming fuel for start-up.

The P0671 code informs you that something in the glow plug circuit is malfunctioning causing the glow plug on cylinder # 1 to not heat up. To find a fault, you need to check the entire circuit.

Note: If DTC P0670 is present in conjunction with this DTC, run diagnostic P0670 before diagnosing this DTC.

Symptoms

If only one glow plug fails, other than the check engine light coming on, symptoms will be minimal as the engine will usually start with one bad plug. In cold conditions, you are more likely to experience this. Code is the main way to identify such a problem.

• The engine control computer (PCM) will set code P0671.
• The engine will be difficult to start or may not start at all in cold weather or when it has been idle long enough to cool the unit.
• Lack of power until the engine has warmed up enough.
• Engine failure can occur due to lower-than-normal cylinder head temperatures.
• Motor may oscillate during acceleration
• There is no preheat period, or in other words, the preheat indicator does not go out.

Possible Causes of Code P0671

Reasons for this DTC may include:

• Defective cylinder # 1 glow plug.
• Open or short circuit in the glow plug circuit
• Damaged wiring connector
• Glow plug control module defective
• Faulty glow plug relay
• Faulty glow plug timer
• Faulty electrical components in the glow plug circuit
• Blown fuses, which may indicate a more serious problem

Diagnostic steps and possible solutions

For a complete test, you will need a digital volt ohm meter (DVOM). Continue testing until the problem is confirmed. You will also need a basic OBD code scanner to restart your computer and erase the code.

Check the glow plug by disconnecting the connecting wire on the plug. Place the DVOM on ohm and place the red wire on the glow plug terminal and the black wire on a good ground. Range is 5 to 2.0 ohms (check measurement for your application referring to factory service manual). If it is out of range, replace the glow plug.

Check the resistance of the glow plug wire to the glow plug relay bus on the valve cover. Note that the relay (similar to the starter relay) has a large gauge wire leading to a bar to which all the glow plug wires are attached. Test the wire to the number one glow plug by placing the red wire on the number one bus wire and the black wire on the side of the glow plug. Again, 5 to 2.0 ohms, with a maximum resistance of 2 ohms. If it is higher, replace the wire to the glow plug from the tire. Also note that these pins from the busbar to the plugs are fusible links. Connect wires.

Check the same wires for looseness, cracks, or lack of insulation. Connect the code scanner to the OBD port under the dashboard and turn the key to the on position with the engine off. Clear codes.

Common Mistakes When Diagnosing Code P0671

While the glow plugs themselves and the electrical components in the glow plug circuit are often to blame for a P0671 code, many technicians report that glow plug timers and relays are often replaced without checking the electrical components and glow plugs.

How serious is the P0671 code?

Code P0671 is a serious problem affecting the vehicle's handling. If not repaired, the car may not start properly or may not start at all in the future.

What repairs can fix code P0671?

There are many ways a technician can troubleshoot a P0671 code. These include:

• Replacing a defective glow plug
• Replacing a faulty glow plug relay
• Replacing a faulty glow plug timer
• Replacing or repairing faulty electrical components in the glow plug circuit
• Replacing Blown Fuses

Additional comments to consider regarding code P0671

When repairing any problem related to glow plugs, safety is very important. When activated, the glow plugs become very hot. Technicians should exercise caution when checking glow plugs for proper function.

How to Fix P0671 Engine Code in 3 Minutes [2 DIY Methods / Only $9.97]

Need more help with your p0671 code?

If you still need help with DTC P0671, post a question in the comments below this article.

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