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P0671 OBD-II Trouble Code: Cylinder 1 Glow Plug Circuit

Check Engine Light

P0671 code definition

The P0671 code indicates that the PCM has detected an abnormal voltage reading from the glow plug circuit in cylinder 1.

What the P0671 code means

Diesel engines require glow plugs to heat cylinders before and during the ignition process. Each cylinder has a glow plug, which uses battery voltage to heat up. The PCM controls the activation of the glow plug circuit, and monitors the activity with voltage readings. If the voltage reading does not match the manufacturer’s specifications, it is likely that the glow plug is not working properly to heat the engine. In this case, the PCM will store the P0671 code.

What causes the P0671 code?

There are many things that can cause the P0671 code. These include:

  • Faulty glow plug
  • Faulty glow plug relay
  • Faulty glow plug timer
  • Faulty electrical components within the glow plug circuit
  • Blown fuses, which could indicate a larger issue

What are the symptoms of the P0671 code?

Most of the time, the vehicle’s owner will notice that the vehicle is taking longer to start, and that the glow plug indicator light never deactivates, or stays on for longer than normal. White smoke may be observed upon start-up; the engine may be considerably louder than normal during start-up; the engine may misfire; and the Check Engine lamp will be illuminated.

How does a mechanic diagnose the P0671 code?

After an OBD-II scanner detects the P0671 code, a technician should begin with a visual inspection of the electrical components, repairing or replacing any damaged components as necessary. After this, and any other repair process, the PCM should be cleared, and the system should be retested, to find out if the repair solved the issue.

If the electrical components were not to blame, the mechanic will begin checking the glow plug connector, the glow plug itself, and fuses, for proper function. Activating the glow plug heater after checking each of these repairs will show the mechanic if there is a short in the circuitry, or if the parts themselves were to blame.

Common mistakes when diagnosing the P0671 code

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

How serious is the P0671 code?

The P0671 code represents a serious issue that affects the drivability of the vehicle. If left unrepaired, the vehicle may not start properly, or at all, in the future.

What repairs can fix the P0671 code?

There are many ways that a technician can address a P0671 code detection. They include:

  • Replacing faulty glow plug
  • Replacing faulty glow plug relay
  • Replacing faulty glow plug timer
  • Replacing or repairing faulty electrical components within the glow plug circuit
  • Replacing blown fuses

Additional comments for consideration regarding the P0671 code

When repairing any issue related to the glow plugs, safety is very important. When activated, glow plugs become extremely hot. Technicians should exercise caution when testing glow plugs for proper functionality.

Need help with a P0671 code?

YourMechanic offers certified mobile mechanics who will come to your home or office to diagnose and repair your vehicle. Get a quote and book an appointment online or speak to a service advisor at 1-800-701-6230.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

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