Ford Power Stroke · Glow Plug Control CircuitMedium

Ford Power Stroke 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 rather than a single plug - check the module first, not individual plugs.

Overview: Ford Power Stroke P-Code P0670

This code is module-level, not plug-level. Confirm the module's power, ground, and communication 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 means the PCM detected a fault in the glow plug control module's circuit, not necessarily an individual glow plug. This module manages power distribution to all glow plugs for cold-start assistance, so a fault here can affect cold-weather starting significantly.

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 or not illuminating

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 first.

Step-by-Step Diagnostic Procedure

  1. Step 1: Locate the glow plug control module, typically mounted near the engine or firewall.
  2. Step 2: Inspect the module's connector for corrosion or a loose pin.
  3. Step 3: Check module power and ground circuits with a multimeter for proper voltage.
  4. Step 4: Test communication between the module and PCM using a scan tool if module diagnostics are supported.
  5. Step 5: Inspect individual glow plug circuits for a short or open that could be affecting the module's ability to control them properly.

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 rather than a plug problem.

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 since those repairs are cheaper.

Will this affect summer driving?

Minimally - glow plugs matter most for cold starts, so summer symptoms are usually mild or absent.

How do I test the module myself?

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

More Ford Power Stroke codes on this system

All Ford Power Stroke fault codes

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