Ram Cummins · Glow Plug Control CircuitMedium

Ram Cummins 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: Ram Cummins 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 Ram Cummins 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.

Module power or ground circuit fault

Common

Insufficient power prevents proper module function.

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: Check the module/circuit level first.

Ignoring the connector condition

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

Do this instead: Inspect and clean the connector first.

Master Tech Commentary

Mechanic's Notes

Shop tip: check module power/ground and connector corrosion first before jumping to individual glow plugs.

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: Check the module's mounting location for heat or moisture damage.

Live Data & Freeze-Frame Tips

Check module communication status on a scan tool for response issues.

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.

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.

Is the module expensive to replace?

It's a moderate cost part - 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/ground plus a scan tool communication check.

More Ram Cummins codes on this system

All Ram Cummins fault codes

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