GM Duramax · Glow Plug Control CircuitMedium

GM Duramax P0670: Glow Plug Control Circuit Malfunction

P-Code P0670 (FMI N/A) — Glow Plug Module Control Circuit Malfunction

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Quick Answer

P0670 means the glow plug control module's circuit has a fault, affecting all glow plugs together - check the module first, not individual plugs.

Overview: GM Duramax P-Code P0670

This code is module-level, not plug-level. Confirm the module's power, ground, and connector condition before replacing any glow plugs.

Repair Snapshot

Time

1 - 3 Hours

Difficulty

Intermediate

Parts Cost

$150 - $400

Dealer Labor

$350+

Tools Required

  • Multimeter
  • Scan Tool
  • Wiring Diagram

What P-Code P0670 Means

P0670 on the Duramax means the PCM detected a fault in the glow plug control module's circuit, affecting all glow plugs together rather than a single plug, which can significantly hurt cold-weather starting.

Symptoms Drivers Notice

  • Hard cold starts, especially in cool or cold weather
  • Excessive white smoke on startup
  • Check engine light
  • Wait-to-start light behaving abnormally

Most Likely Root Causes

Corroded or loose module connector

Common

Poor connection disrupts the module's ability to control glow plugs properly.

Module power or ground circuit fault

Common

Insufficient power prevents the module from functioning correctly.

Internal module failure

Occasional

The module itself can fail after extended service life.

Common Misdiagnoses (Don't Waste Parts)

Replacing individual glow plugs first

Why it happens: Glow plug issues are commonly associated with hard starts.

Do this instead: This code points to the module/circuit level - check that before replacing plugs.

Ignoring the connector condition

Why it happens: Focus goes straight to the module itself.

Do this instead: Inspect and clean the connector first - it resolves many cases without a module replacement.

Master Tech Commentary

Mechanic's Notes

Shop tip: don't jump straight to individual glow plugs - this code specifically points to the control module or its circuit. Check module power/ground and connector corrosion first.

Step-by-Step Diagnostic Procedure

  1. Step 1: Locate the glow plug control module and inspect its connector for corrosion.
  2. Step 2: Check module power and ground circuits with a multimeter.
  3. Step 3: Test communication between the module and PCM using a scan tool.
  4. Step 4: Inspect individual glow plug circuits for a short or open affecting the module.
  5. Step 5: Verify the module mounting and heat sink area isn't corroded, a known issue on some Duramax model years.

Live Data & Freeze-Frame Tips

Check module communication status on a scan tool - a module that isn't responding to commands points to a power, ground, or communication issue.

Safety Warnings

  • Allow the engine to cool before working near glow plug circuits.
  • Disconnect the battery before extensive electrical diagnosis.

When to Limp In vs Tow

Not required - the truck remains driveable in most weather, though cold starts may be difficult.

Prevention Tips for Fleets & Owner-Operators

  • Inspect the module connector during routine maintenance.
  • Address hard-start symptoms early before winter.
  • Keep the module area free of moisture intrusion.

Related Fault Codes

P0671

Individual glow plug circuit fault for cylinder 1, a more specific version of a glow plug problem.

Frequently Asked Questions

Does this mean all my glow plugs are bad?

Not necessarily - this code points to the control module or its circuit, which manages all plugs together.

Can I still drive with this code?

Yes, though cold starts may be difficult, especially in cool or cold weather.

Is the module expensive to replace?

It's a moderate cost part, but always confirm the connector and wiring first.

Will this affect summer driving?

Minimally - glow plugs matter most for cold starts.

How do I test the module myself?

A multimeter check of power and ground circuits, combined with a scan tool communication check.