P0670 — Glow Plug Module Control Circuit
P0670 indicates a fault in the glow plug module control circuit or communication with the ECM. Individual plug testing before module replacement prevents repeat failures — one shorted plug can kill the module.
Fault Overview
Failed glow plug module, open or shorted control circuit, power or ground issues, failed individual glow plugs overloading the module, and connector problems are the primary causes. Test individual glow-plug resistance before replacing the module. Poor grounds are a common cause of module faults.
Engine & Platform Coverage
Symptoms
- •P0670
- •glow plug module
- •GPCM circuit
- •glow plug control fault
- •cold start glow plug
Possible Causes
- 1.Failed glow plug module
- 2.Open or shorted control circuit
- 3.Power or ground issues
- 4.Failed individual glow plugs overloading the module
- 5.Connector problems
Wiring & Circuit Notes
GPCM power, ground, control, and communication circuits. Check for heat damage near the module.
DVOM Specs & Sensor Tests
Module power and ground under load. Control signal from ECM. Individual glow-plug resistance (typically 0.5–2 Ω for a good plug). Current draw of the bank.
Diagnostic Flow — FSM Sequence
AI Diesel Tech enforces this evidence-gate sequence. Each gate must pass before advancing.
4 steps locked behind Technician Mode- 1Step 1 — Verify Battery Voltage and GPCM Power/Ground: Verify battery voltage and GPCM power and ground under load. Poor grounds are a common cause of module faults.
- 2Step 2 — Measure Individual Glow-Plug Resistance: Measure individual glow-plug resistance. A shorted plug (near 0 Ω) can damage or destroy the module.
- 3Step 3 — Check Control Circuit from ECM: Check the control circuit from the ECM to the GPCM for opens or shorts.
- 4Step 4 — Monitor Current Draw During Glow Cycle: Monitor total current draw during the glow cycle. Excessive current indicates a shorted plug.
- 5Step 5 — Replace Module Only After Plugs and Wiring Are Proven Good: Replace the GPCM only after all individual glow plugs and wiring are proven good.
Unlock the full evidence-gated diagnostic sequence, DVOM test steps, and repair procedures in Technician Mode.
Full Diagnostic Access
Verification steps, preventative measures, severity guidance, and legacy comparison are available in Technician Mode.
Typical Repair Costs
Replace failed glow plugs $50–300; repair wiring/grounds $80–200; replace GPCM $200–600.
Start Diagnosing This Fault Now
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Summary
Use the AI Diesel Tech diagnostic engine to run this code through a structured, evidence-gated sequence and get a confirmed root cause before any parts are replaced.