How to Fix the P0671 DTC Code on Duramax (Expert Insights)

If you own a Duramax engine, you’re probably used to seeing Diagnostic Trouble Codes (DTC). It can be annoying, but at the same time, the diagnostic trouble codes help you to specify a fault in your Duramax engine and fix it earlier.

The DTC P0671 means the Glow Plug Circuit in cylinder number one of Duramax is malfunctioning or is damaged. Other associative errors, such as a defective Glow Plug Module, can cause a similar trouble code in OBD-II.

All these may seem a little confusing and tricky. Reading this article will let you grasp the correct approach to detecting symptoms and causes and executing potential fixes.

What Does P0671 Code Mean On Duramax?

The Po671 trouble code means the glow plug circuit module of cylinder one is not working correctly. The powertrain computer module detects an atypical voltage reading from the Glow Plug Module.

If we elaborate on the entire code, it gives something like this.

  • P = Powertrain, the system of components that propels your car forward.
  • 0 = a generic number derived from the SAE standard
  • 6 = Glow Plug Circuit
  • 71 = Specific fault index (Fault in GlowPlug Circuit Cylinder #1)

Unlike gasoline engines, heavy diesel engines require a glow plug to heat the combustion chamber wall to assist ignition. The onboard PCM controls the voltage input and output through the glow plug.

When the output voltage of the glow plug fails to sync with the manufacturer’s specification, it shows the P0671 DTC.

How Serious Is P0671 Code On Duramax?

The Duramax is an eight-cylinder diesel engine that relies on glow plugs for a cold start. For a Duramax engine, DTC P0671 is a moderately severe error.

Primarily if you reside in a cold region, your truck may not turn over due to a lack of preheating of cylinder #1. Along with that, the engine performance and driveability of the car degrade with time.

If not treated on time, the P0671 can actively assist in causing other problems in the engine. In some regions, driving a vehicle with the check engine light turned on is illegal. That means you may get pulled over and fined by the cops.

Misfires, no engine power, and no ignition/hard ignition are some of the most common P0671 problems. That is why it is recommended to fix P0671 as soon as possible.

What Causes P0671 Code On Duramax?

A damaged or defective Glow Plug in Cylinder #1 is the most common cause of a P0671 DTC.  However, P0671 in OBD-II can be caused by various other factors.

  • Open/Shorted circuit of Glow Plug.
  • Faulty Glow Plug Module.
  • Damage to the connecting wires
  • Faulty Glow Plug relay.

How To Fix The P0671 Code On Duramax?

Since the errors are variable and can be caused by one or multiple issues, fixing the P0671 in Duramax requires a fixing sequence. Starting from getting freeze frame data to repair/replace the parts can fix this problem.

Step 1: Retrieving Freeze Frame Data

Being manufactured after 1996, the Duramax engine is compatible with the OBD-II system. Connect your OBD-II scanning device to the OBD-II port of the truck.

Turn over the engine and run a complete diagnostic scan of your vehicle. After scanning, note down the freeze frame data for further comparison and assistance.

Step 2: Inspect and Replace Glow Plugs

There are eight glow plugs for eight cylinders of the Duramax engine. When the glow plug of Cylinder #1 gets damaged, the P0671 is set. To access the glow plugs, you need to disassemble the vehicle fenders.

Cylinders #1,3,5,7 are located below the passenger side. Take out the glow plug and use a multimeter to check its resistance. In general, the glow plug resistance is bound within 0.5 to 2ohm.

Anything above the limit means it has been damaged and requires replacement because repairing glow plugs is impossible. Moreover, you may need to inspect and replace the entire set of glow plugs on each side.

Step 3: Inspection of resistance in the associative parts of the Glow Plug

Using a multimeter/digital volt meter, check the resistance of the glow plug wire to the bus bar. To track, inspect the relay with a wire harness leading to the bar where all the glow plug wires are connected.

Look for the wire of the glow plug from Cylinder #1. The resistance range for the wire would be 0.5 to 2 ohms. If it deviates from the range, replace the entire wire lead from the glow plug.

Step 4: Check other electric connections

Check all the relay and glow plug control module wires for physical degradation such as broken, loose, or cracked wires. If found any, you need to install a new set of cables.

Step 5: Glow Plug Control Module

Pop the truck’s hood and remove the Glow plug control module from the engine side. Check the module for any physical damage or contamination from other engine parts. You may also check the connecting pins of the module.

If any problem is found, it is better to involve a professional for replacement or repair. Lastly, connect the OBD-II and clear all the codes turning on the panel. Switch off to check if the scanner is still showing the codes.

Other Symptoms Of Getting P0671 Code On Duramax

Taking too much time cranking and not getting your truck started is a significant symptom of DTC P0671. However, some other symptoms can be used to detect the issue earlier and save the engine from further damage.

  • Several misfires until the engine turns over
  • The machine does not start at all.
  • Lack of acceleration
  • Decrement of engine power until heated sufficiently
  • The Check Engine Light turns on in the instrumental panel

How Much Does It Cost To Fix Duramax P0671 Code?

If you head to a mechanic in a workshop, the initial diagnosis may take up to $70 to $150 per hour. To replace each glow plug, you need to spend $12 to $26, depending upon the current price and brand.

Replacing the glow plug module is expensive, and the cost depends upon location, current rate, etc.

Can You Drive Your Duramax With Code P0671?

Initially, you can drive your truck until the engine is warm enough for ignition. But in, cold regions and low temperatures can set your engine to idle, and P0671 will cause no cranking or hard cranking.

Your car may get stalled on a road while you drive. Besides, lack of power output and acceleration can affect driveability. That is why it is recommended to only drive the truck with P0671 to reach a workshop rather than on freeways.


The DTC P0671 is a comparatively simple and inexpensive issue for your Duramax engine. You can diagnose and repair the glow plugs in your home garage using some essential tools.

But it is recommended to seek a professional opinion if the issue is complex and found in the Glow Plug Control Module. We expect you have learned about the probable causes and symptoms of P0671 sooner. Treating the P0671 as early as possible can save your engine from additional damage.

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