Code
P0677
Generic
P — Powertrain
Cylinder 7 Glow Plug Circuit/Open
Views:
UK: 21
EN: 34
RU: 15
AI status
Completed
Completed
100%
Causes
- Failed glow plug in cylinder 7
- Open or shorted wiring between glow plug and relay/ECM
- Corroded or loose connector at the glow plug or harness
- Failed glow plug relay or fuse
- Poor battery voltage or ground to glow plug circuit
- High-resistance connection (corrosion, damaged terminal)
Symptoms
- Glow plug warning or check engine lamp illuminated
- Hard or extended cranking on cold start
- Rough idle or misfire during cold start
- Increased white smoke or visible unburned fuel on cold start
- Longer engine warm-up time
What to check
- Read and record freeze frame and related codes with a scan tool
- Visually inspect glow plug harness, connectors and grounds at cylinder 7 for corrosion, damage or loose terminals
- Check battery voltage (should be ~12–14 V) and condition before testing circuit
- Inspect relevant glow plug fuse(s) and relay(s) for continuity and proper operation
- Measure resistance of the cylinder 7 glow plug with the plug disconnected from harness
- Back-probe glow plug connector during preheat command and verify voltage/current present
Signal parameters
- Glow plug supply voltage during preheat: typically ~11–14 V (battery voltage)
- Glow plug resistance (typical): ~0.4–2.0 Ω per plug (varies by engine)
- Current draw per glow plug during preheat: commonly ~5–20 A (depends on design)
- ECM control type: switched ground or switched positive; may use PWM/duty-cycle control for temperature regulation
- Expected ECU feedback: closed circuit/current detected when commanded; open circuit indicated by no current/very high resistance
Diagnostic algorithm
- Retrieve all codes and freeze-frame data; note battery voltage at time of fault. 2) Visually inspect wiring, connectors and grounds for cylinder 7; repair obvious damage or corrosion. 3) With ignition off, disconnect the cylinder 7 glow plug and measure its resistance to ground; compare to manufacturer spec and to other cylinders. 4) Check fuse(s) and relay(s) in the glow plug circuit for continuity and proper operation; replace if faulty. 5) With a fully charged battery, command glow plugs ON using a scan tool and measure voltage at the cylinder 7 connector; if voltage present but no current, suspect the glow plug. 6) If no voltage at connector when commanded, trace/inspect wiring back to relay/ECM and test for continuity to the relay and control signal from ECM. 7) Measure current draw of the cylinder 7 glow plug while commanded; a much lower or zero current compared to other cylinders indicates open/faulty plug or wiring. 8) If wiring and glow plug test good, test the glow plug driver output at the ECM for proper switching; if ECM output is faulty, consult manufacturer procedures before replacing ECM. 9) After repairs or replacements, clear codes and perform multiple cold start cycles to verify the fault does not return.
Likely causes
- Single glow plug open or burned out at cylinder 7
- Broken wire or damaged insulation in the cylinder 7 harness leg
- Loose/corroded terminal at the cylinder 7 glow plug connector
- Failed glow plug relay or blown fuse affecting cylinder 7 circuit
Fault status
Status
Open or fault detected in cylinder 7 glow plug circuit — ECM did not detect expected current/closure when commanding cylinder 7 glow plug.
Repair difficulty: Medium
Diagnostic time: 1.0-2.5 hours
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Code
P0677
LAND ROVER
P — Powertrain
Cylinder 7 glow plug - open circuit
Views:
UK: 5
EN: 20
RU: 5
AI status
Completed
Completed
100%
Causes
- Failed glow plug in cylinder 7
- Open or shorted wiring between glow plug and relay/ECM
- Corroded or loose connector at the glow plug or harness
- Failed glow plug relay or fuse
- Poor battery voltage or ground to glow plug circuit
- High-resistance connection (corrosion, damaged terminal)
Symptoms
- Glow plug warning or check engine lamp illuminated
- Hard or extended cranking on cold start
- Rough idle or misfire during cold start
- Increased white smoke or visible unburned fuel on cold start
- Longer engine warm-up time
What to check
- Read and record freeze frame and related codes with a scan tool
- Visually inspect glow plug harness, connectors and grounds at cylinder 7 for corrosion, damage or loose terminals
- Check battery voltage (should be ~12–14 V) and condition before testing circuit
- Inspect relevant glow plug fuse(s) and relay(s) for continuity and proper operation
- Measure resistance of the cylinder 7 glow plug with the plug disconnected from harness
- Back-probe glow plug connector during preheat command and verify voltage/current present
Signal parameters
- Glow plug supply voltage during preheat: typically ~11–14 V (battery voltage)
- Glow plug resistance (typical): ~0.4–2.0 Ω per plug (varies by engine)
- Current draw per glow plug during preheat: commonly ~5–20 A (depends on design)
- ECM control type: switched ground or switched positive; may use PWM/duty-cycle control for temperature regulation
- Expected ECU feedback: closed circuit/current detected when commanded; open circuit indicated by no current/very high resistance
Diagnostic algorithm
- Retrieve all codes and freeze-frame data; note battery voltage at time of fault. 2) Visually inspect wiring, connectors and grounds for cylinder 7; repair obvious damage or corrosion. 3) With ignition off, disconnect the cylinder 7 glow plug and measure its resistance to ground; compare to manufacturer spec and to other cylinders. 4) Check fuse(s) and relay(s) in the glow plug circuit for continuity and proper operation; replace if faulty. 5) With a fully charged battery, command glow plugs ON using a scan tool and measure voltage at the cylinder 7 connector; if voltage present but no current, suspect the glow plug. 6) If no voltage at connector when commanded, trace/inspect wiring back to relay/ECM and test for continuity to the relay and control signal from ECM. 7) Measure current draw of the cylinder 7 glow plug while commanded; a much lower or zero current compared to other cylinders indicates open/faulty plug or wiring. 8) If wiring and glow plug test good, test the glow plug driver output at the ECM for proper switching; if ECM output is faulty, consult manufacturer procedures before replacing ECM. 9) After repairs or replacements, clear codes and perform multiple cold start cycles to verify the fault does not return.
Likely causes
- Single glow plug open or burned out at cylinder 7
- Broken wire or damaged insulation in the cylinder 7 harness leg
- Loose/corroded terminal at the cylinder 7 glow plug connector
- Failed glow plug relay or blown fuse affecting cylinder 7 circuit
Fault status
Status
Open or fault detected in cylinder 7 glow plug circuit — ECM did not detect expected current/closure when commanding cylinder 7 glow plug.
Repair difficulty: Medium
Diagnostic time: 1.0-2.5 hours
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Land Rover Defender 300Tdi — Workshop Manual (1996 model year)
Workshop Manual199,00 UAH
Land Rover Defender Workshop Manual Supplement & Body Repair Manual (1999 & 2002 MY)
Workshop Manual199,00 UAH
Land Rover Range Rover — Electrical Library (LRL 0453ENG, 2002)
Workshop Manual199,00 UAH
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