P0674

Code

Generic P — Powertrain

Cylinder 4 Glow Plug Circuit/Open

Brand: Generic

Type: P — Powertrain

Views: UK: 35 EN: 184 RU: 46

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Page language: EN

Causes

Open circuit in wiring to glow plug (broken wire, connector disconnected)
Failed glow plug (open internal element)
Corroded or loose glow plug connector or terminal
Faulty glow plug relay, fuse, or control module
Faulty ECM/engine control driver for glow plug circuit
Shorted wiring to ground or to other circuits (less common)

Symptoms

Hard starting when engine is cold (single cylinder may contribute)
Extended crank time or increased white smoke on cold start
Glow plug warning light or glow plug indicator on dash (on some vehicles)
Possible rough idle until engine warms (less common)
Stored P0674 trouble code and possible related misfire codes

What to check

Retrieve freeze-frame and live data with a scan tool; confirm P0674 and check glow plug status/commands
Perform visual inspection of glow plug, connector, and wiring for damage or corrosion
Check fuse(s) and relay(s) for glow plug/heater circuit
Backprobe cylinder 4 glow plug connector and measure voltage while the ECM commands glow plug on
Measure glow plug resistance (at room temperature) and compare to specification or other cylinders
Perform current draw test on cylinder 4 glow plug when commanded (or swap with another cylinder to compare)

Signal parameters

Glow plug resistance (cold, typical): approx. 0.3–3.0 ohms (varies by vehicle and glow plug type) — open = infinite ohms
Supply voltage (when commanded): approx. battery voltage (11–14 V) at connector (may be pulsed/PWM)
Current draw (individual glow plug): typically 2–15 A when energized (varies by design)
ECM/driver command: ON or PWM duty cycle reported by scan tool when preheat is active
Open-circuit indicator: no voltage or no current at glow plug connector when commanded

Diagnostic algorithm

Read and record freeze frame and live data. Confirm P0674 is current or history and note battery voltage at test time.
Visually inspect glow plug #4, connector and wiring for corrosion, loose pins, heat damage, or contamination. Repair any visible damage.
Check glow plug supply fuse(s) and relay(s). Replace if blown or faulty and retest.
With harness connector disconnected, measure resistance of glow plug #4 to ground. If infinite or out of spec, replace the glow plug.
With a helper or appropriate equipment, command glow plugs ON and backprobe the connector; measure voltage and/or current. No voltage or no current indicates open/harness/driver issue.
If supply voltage is present but glow plug shows open, replace the glow plug and re-test. If glow plug functions when swapped to another cylinder, the original glow plug was faulty.
If glow plug tests good but no command/current is present, check continuity between the glow plug connector and the glow plug driver/module, inspect wiring for shorts/opens, and test the driver relay/module per factory procedure.
If wiring and module tests normal, inspect ECM/driver outputs; consult vehicle-specific wiring diagrams. Replace faulty driver/module or repair wiring as required.
Clear codes and perform functional test and road/starting verification to ensure code does not return.
Safety note: Glow plugs draw high current and can be hot. Use insulated tools, avoid shorting terminals, and disconnect battery when performing replacements unless testing live conditions explicitly.

Likely causes

Open/poor connection at the cylinder 4 glow plug connector or terminal
Glow plug element for cylinder 4 has failed open
Blown fuse or failed relay for glow plug supply circuit
Damaged harness (chafing, heat damage) between glow plug and glow plug module/ECM
Faulty glow plug driver module or ECM output for cylinder 4