P0677

Code

Generic P — Powertrain

Cylinder 7 Glow Plug Circuit/Open

Brand: Generic

Type: P — Powertrain

Views: UK: 30 EN: 69 RU: 25

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Page language: EN

Causes

Failed glow plug (open or internally damaged) at cylinder 7
Broken or corroded wiring/connector at the cylinder 7 glow plug
Poor or missing ground at glow plug or harness
Blown fuse or faulty glow plug relay/module/power driver
High resistance in circuit (loose connection, corrosion)
ECM/PCM driver fault or internal failure

Symptoms

Check Engine MIL illuminated (DTC P0677)
Hard starting when engine is cold or in cold ambient temperatures
Extended cranking or prolonged white smoke on startup
Rough idle immediately after cold start
Glow/plugs/wait-to-start lamp may flash or behave abnormally

What to check

Retrieve freeze frame and related codes; confirm P0677 is current and not intermittent
Inspect glow plug wiring, connectors, and harness near cylinder 7 for corrosion, damage, or loose pins
Inspect and test glow plug power supply fuses and glow relay/module for proper operation
Compare resistance of cylinder 7 glow plug to other cylinders with plug removed and engine off
Backprobe glow plug connector to check for battery voltage during preheat cycle (key ON/engine start)
Check continuity from glow plug connector back to the glow relay/module/ECM and confirm good ground

Signal parameters

Expected supply voltage at glow plug connector when preheating: close to battery voltage (~12 V nominal)
Glow plug resistance (typical range): roughly 0.5–3.0 ohms for many designs — compare to identical plugs on other cylinders
Current draw: glow plugs are high-current devices; individual plug draw commonly several amps (varies by design) — a dead/open plug will show no current

Diagnostic algorithm

Safety: park vehicle, engage parking brake, allow engine to cool. If you will probe connectors, follow manufacturer battery/disconnect guidance.
Read and record codes and freeze-frame data. Clear code then perform a controlled test to see if code returns.
Perform visual inspection of harness and connector at cylinder 7 for damage, corrosion, or overheating. Repair as needed.
With ignition OFF, remove glow plug #7 and measure its DC resistance with a multimeter. Compare to the same-spec glow plugs on other cylinders. An open (infinite) reading indicates a failed plug.
Reconnect plug. With ignition ON during preheat (or using a scan tool to activate glow) backprobe the power terminal at the cylinder 7 connector. Verify battery voltage is present when the system is commanding preheat.
If voltage is present but plug shows open/infinite resistance, replace the glow plug and retest.
If no voltage at connector, check fuse(s), relay(s), and wiring continuity from the relay/module to the plug. Repair broken wiring, poor pin contacts, or grounds.
If wiring, power, and fuses/relays are OK but no activation, test the glow plug driver/module output and related ECM signals using diagnostics or swap drivers (if serviceable) to isolate module vs ECM. Consult repair manual for driver-pin tests.
After repairs, clear codes and perform cold-start verification to ensure the code does not return.
If intermittent, inspect for harness rubbing/chafing and perform wiggle tests while observing live data to reproduce the fault.