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Home / DTC / P1027 — Glow plugs, cylinders 1/2/3 - circuit malfunction

P1027 — Glow plugs, cylinders 1/2/3 - circuit malfunction

Detailed page for trouble code P1027.

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P1027

DACIA P — Powertrain

Glow plugs, cylinders 1/2/3 - circuit malfunction

Brand: DACIA
Type: P — Powertrain
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Open or short in glow plug wiring harness for cylinders 1–3
  • Failed glow plugs (one or more of cylinders 1, 2, 3)
  • Faulty glow plug relay or fuse
  • Poor ground connection at engine or glow plug rail
  • Corroded/loose connector(s) at glow plugs or ECU
  • Faulty ECU/driver transistor controlling glow plug circuits

Symptoms

  • Difficult or lengthy cold starting
  • Glow plug indicator or MIL/wrench lamp illuminated
  • Rough idle or misfire immediately after cold start
  • Increased white smoke or poor emissions on cold start
  • Possible stored related fault codes in ECU

What to check

  • Read and record all stored and pending codes and freeze-frame data with a capable scan tool
  • Visually inspect glow plug harness, connectors and grounds for damage or corrosion
  • Check fuse(s) and glow plug relay operation
  • Measure battery voltage (good charged battery required for valid tests)
  • Command preheat on with scan tool and observe glow-plug indicator / relay click
  • Measure voltage at the glow plug supply rail and at individual plug connectors during preheat

Signal parameters

  • Nominal battery voltage: ~12.0–14.5 V (engine off/charging) at supply rail
  • Glow plug DC resistance (typical): ~0.5–3 Ω per plug (varies by plug type) — open or very high values indicate failed plug
  • Current draw per glow plug: typically several amps (often 3–20 A depending on plug and engine); simultaneous current for multiple plugs will be higher
  • With preheat commanded the ECU/relay should apply near battery voltage to the glow plug rail; significant voltage drop indicates high resistance or poor supply/ground
  • If ECU uses PWM, check for switched voltage waveform on control side using oscilloscope or appropriate scan-tool data

Diagnostic algorithm

  1. Verify the code with a scan tool, clear codes and attempt to re-run preheat cycle to see if code returns; note any other related codes.
  2. Perform a visual inspection of the glow plug harness, connectors, fuse(s) and relay for damage, melted insulation, corrosion or loose pins.
  3. Check battery condition and charging system voltage to ensure valid testing conditions.
  4. With key on (preheat commanded) use a voltmeter to confirm battery voltage is present at the glow plug supply rail / relay output. If supply missing, test relay and fuse.
  5. Backprobe each glow plug connector (cylinders 1, 2, 3) while preheat is commanded and record voltage; compare to battery voltage. Large drop indicates high resistance or poor connection.
  6. With engine off and battery disconnected, measure resistance of each glow plug to engine block ground. Compare values across plugs; an open or significantly higher/lower value indicates a failed plug.
  7. If individual glow plugs appear faulty, replace the suspect plugs. If all three share high resistance, inspect harness and common feed/ground.
  8. If voltage at plug connector is correct but plug resistance is good, suspect ECU driver; test ECU output (scope recommended) and verify wiring continuity back to ECU.
  9. After repairs, clear codes and perform multiple cold start cycles to confirm the fault does not return.
  10. Safety note: Glow plug circuits carry high current; avoid shorting terminals, and use insulated tools. Allow engine to cool before removing glow plugs.

Likely causes

  • Broken wiring or corroded connector feeding glow plugs 1–3
  • One or more glow plugs for cylinders 1, 2 or 3 have failed (open or short)
  • Failed preheat/relay or blown fuse reducing supply voltage to multiple plugs
  • Poor ground at engine block or glow plug return common point
  • ECU output driver fault (less common)

Fault status

⚠️ Status
Glow plugs, cylinders 1/2/3 - circuit malfunction. ECU detects abnormal resistance/voltage/current in glow plug circuits for cylinders 1, 2 and 3. Further electrical checks required to locate fault.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5-2 hours

Similar codes

P0670 P0671 P0672 P0673 P0674 P1026
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Code

P1027

MITSUBISHI P — Powertrain

Oil control Valve 2 open(Ex)

Brand: MITSUBISHI
Type: P — Powertrain
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Open or short in glow plug wiring harness for cylinders 1–3
  • Failed glow plugs (one or more of cylinders 1, 2, 3)
  • Faulty glow plug relay or fuse
  • Poor ground connection at engine or glow plug rail
  • Corroded/loose connector(s) at glow plugs or ECU
  • Faulty ECU/driver transistor controlling glow plug circuits

Symptoms

  • Difficult or lengthy cold starting
  • Glow plug indicator or MIL/wrench lamp illuminated
  • Rough idle or misfire immediately after cold start
  • Increased white smoke or poor emissions on cold start
  • Possible stored related fault codes in ECU

What to check

  • Read and record all stored and pending codes and freeze-frame data with a capable scan tool
  • Visually inspect glow plug harness, connectors and grounds for damage or corrosion
  • Check fuse(s) and glow plug relay operation
  • Measure battery voltage (good charged battery required for valid tests)
  • Command preheat on with scan tool and observe glow-plug indicator / relay click
  • Measure voltage at the glow plug supply rail and at individual plug connectors during preheat

Signal parameters

  • Nominal battery voltage: ~12.0–14.5 V (engine off/charging) at supply rail
  • Glow plug DC resistance (typical): ~0.5–3 Ω per plug (varies by plug type) — open or very high values indicate failed plug
  • Current draw per glow plug: typically several amps (often 3–20 A depending on plug and engine); simultaneous current for multiple plugs will be higher
  • With preheat commanded the ECU/relay should apply near battery voltage to the glow plug rail; significant voltage drop indicates high resistance or poor supply/ground
  • If ECU uses PWM, check for switched voltage waveform on control side using oscilloscope or appropriate scan-tool data

Diagnostic algorithm

  1. Verify the code with a scan tool, clear codes and attempt to re-run preheat cycle to see if code returns; note any other related codes.
  2. Perform a visual inspection of the glow plug harness, connectors, fuse(s) and relay for damage, melted insulation, corrosion or loose pins.
  3. Check battery condition and charging system voltage to ensure valid testing conditions.
  4. With key on (preheat commanded) use a voltmeter to confirm battery voltage is present at the glow plug supply rail / relay output. If supply missing, test relay and fuse.
  5. Backprobe each glow plug connector (cylinders 1, 2, 3) while preheat is commanded and record voltage; compare to battery voltage. Large drop indicates high resistance or poor connection.
  6. With engine off and battery disconnected, measure resistance of each glow plug to engine block ground. Compare values across plugs; an open or significantly higher/lower value indicates a failed plug.
  7. If individual glow plugs appear faulty, replace the suspect plugs. If all three share high resistance, inspect harness and common feed/ground.
  8. If voltage at plug connector is correct but plug resistance is good, suspect ECU driver; test ECU output (scope recommended) and verify wiring continuity back to ECU.
  9. After repairs, clear codes and perform multiple cold start cycles to confirm the fault does not return.
  10. Safety note: Glow plug circuits carry high current; avoid shorting terminals, and use insulated tools. Allow engine to cool before removing glow plugs.

Likely causes

  • Broken wiring or corroded connector feeding glow plugs 1–3
  • One or more glow plugs for cylinders 1, 2 or 3 have failed (open or short)
  • Failed preheat/relay or blown fuse reducing supply voltage to multiple plugs
  • Poor ground at engine block or glow plug return common point
  • ECU output driver fault (less common)

Fault status

⚠️ Status
Glow plugs, cylinders 1/2/3 - circuit malfunction. ECU detects abnormal resistance/voltage/current in glow plug circuits for cylinders 1, 2 and 3. Further electrical checks required to locate fault.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5-2 hours

Similar codes

P0670 P0671 P0672 P0673 P0674 P1026
406

Browse 406 MITSUBISHI manuals: repair procedures, diagnostics, wiring diagrams, component locations, service data and Labor Times by year, model and trim.

MITSUBISHI

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Keep it short and practical. Up to 500 characters.
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Code

P1027

RAM P — Powertrain

ECU Sees Wide Open Throttle

Brand: RAM
Type: P — Powertrain
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Open or short in glow plug wiring harness for cylinders 1–3
  • Failed glow plugs (one or more of cylinders 1, 2, 3)
  • Faulty glow plug relay or fuse
  • Poor ground connection at engine or glow plug rail
  • Corroded/loose connector(s) at glow plugs or ECU
  • Faulty ECU/driver transistor controlling glow plug circuits

Symptoms

  • Difficult or lengthy cold starting
  • Glow plug indicator or MIL/wrench lamp illuminated
  • Rough idle or misfire immediately after cold start
  • Increased white smoke or poor emissions on cold start
  • Possible stored related fault codes in ECU

What to check

  • Read and record all stored and pending codes and freeze-frame data with a capable scan tool
  • Visually inspect glow plug harness, connectors and grounds for damage or corrosion
  • Check fuse(s) and glow plug relay operation
  • Measure battery voltage (good charged battery required for valid tests)
  • Command preheat on with scan tool and observe glow-plug indicator / relay click
  • Measure voltage at the glow plug supply rail and at individual plug connectors during preheat

Signal parameters

  • Nominal battery voltage: ~12.0–14.5 V (engine off/charging) at supply rail
  • Glow plug DC resistance (typical): ~0.5–3 Ω per plug (varies by plug type) — open or very high values indicate failed plug
  • Current draw per glow plug: typically several amps (often 3–20 A depending on plug and engine); simultaneous current for multiple plugs will be higher
  • With preheat commanded the ECU/relay should apply near battery voltage to the glow plug rail; significant voltage drop indicates high resistance or poor supply/ground
  • If ECU uses PWM, check for switched voltage waveform on control side using oscilloscope or appropriate scan-tool data

Diagnostic algorithm

  1. Verify the code with a scan tool, clear codes and attempt to re-run preheat cycle to see if code returns; note any other related codes.
  2. Perform a visual inspection of the glow plug harness, connectors, fuse(s) and relay for damage, melted insulation, corrosion or loose pins.
  3. Check battery condition and charging system voltage to ensure valid testing conditions.
  4. With key on (preheat commanded) use a voltmeter to confirm battery voltage is present at the glow plug supply rail / relay output. If supply missing, test relay and fuse.
  5. Backprobe each glow plug connector (cylinders 1, 2, 3) while preheat is commanded and record voltage; compare to battery voltage. Large drop indicates high resistance or poor connection.
  6. With engine off and battery disconnected, measure resistance of each glow plug to engine block ground. Compare values across plugs; an open or significantly higher/lower value indicates a failed plug.
  7. If individual glow plugs appear faulty, replace the suspect plugs. If all three share high resistance, inspect harness and common feed/ground.
  8. If voltage at plug connector is correct but plug resistance is good, suspect ECU driver; test ECU output (scope recommended) and verify wiring continuity back to ECU.
  9. After repairs, clear codes and perform multiple cold start cycles to confirm the fault does not return.
  10. Safety note: Glow plug circuits carry high current; avoid shorting terminals, and use insulated tools. Allow engine to cool before removing glow plugs.

Likely causes

  • Broken wiring or corroded connector feeding glow plugs 1–3
  • One or more glow plugs for cylinders 1, 2 or 3 have failed (open or short)
  • Failed preheat/relay or blown fuse reducing supply voltage to multiple plugs
  • Poor ground at engine block or glow plug return common point
  • ECU output driver fault (less common)

Fault status

⚠️ Status
Glow plugs, cylinders 1/2/3 - circuit malfunction. ECU detects abnormal resistance/voltage/current in glow plug circuits for cylinders 1, 2 and 3. Further electrical checks required to locate fault.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5-2 hours

Similar codes

P0670 P0671 P0672 P0673 P0674 P1026
Your experience will help others
+100 karma for a short comment :)
Keep it short and practical. Up to 500 characters.
Send to email
Code

P1027

RENAULT P — Powertrain

- Glow plugs, cylinders 1/2/3 - circuit malfunction

Brand: RENAULT
Type: P — Powertrain
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Open or short in glow plug wiring harness for cylinders 1–3
  • Failed glow plugs (one or more of cylinders 1, 2, 3)
  • Faulty glow plug relay or fuse
  • Poor ground connection at engine or glow plug rail
  • Corroded/loose connector(s) at glow plugs or ECU
  • Faulty ECU/driver transistor controlling glow plug circuits

Symptoms

  • Difficult or lengthy cold starting
  • Glow plug indicator or MIL/wrench lamp illuminated
  • Rough idle or misfire immediately after cold start
  • Increased white smoke or poor emissions on cold start
  • Possible stored related fault codes in ECU

What to check

  • Read and record all stored and pending codes and freeze-frame data with a capable scan tool
  • Visually inspect glow plug harness, connectors and grounds for damage or corrosion
  • Check fuse(s) and glow plug relay operation
  • Measure battery voltage (good charged battery required for valid tests)
  • Command preheat on with scan tool and observe glow-plug indicator / relay click
  • Measure voltage at the glow plug supply rail and at individual plug connectors during preheat

Signal parameters

  • Nominal battery voltage: ~12.0–14.5 V (engine off/charging) at supply rail
  • Glow plug DC resistance (typical): ~0.5–3 Ω per plug (varies by plug type) — open or very high values indicate failed plug
  • Current draw per glow plug: typically several amps (often 3–20 A depending on plug and engine); simultaneous current for multiple plugs will be higher
  • With preheat commanded the ECU/relay should apply near battery voltage to the glow plug rail; significant voltage drop indicates high resistance or poor supply/ground
  • If ECU uses PWM, check for switched voltage waveform on control side using oscilloscope or appropriate scan-tool data

Diagnostic algorithm

  1. Verify the code with a scan tool, clear codes and attempt to re-run preheat cycle to see if code returns; note any other related codes.
  2. Perform a visual inspection of the glow plug harness, connectors, fuse(s) and relay for damage, melted insulation, corrosion or loose pins.
  3. Check battery condition and charging system voltage to ensure valid testing conditions.
  4. With key on (preheat commanded) use a voltmeter to confirm battery voltage is present at the glow plug supply rail / relay output. If supply missing, test relay and fuse.
  5. Backprobe each glow plug connector (cylinders 1, 2, 3) while preheat is commanded and record voltage; compare to battery voltage. Large drop indicates high resistance or poor connection.
  6. With engine off and battery disconnected, measure resistance of each glow plug to engine block ground. Compare values across plugs; an open or significantly higher/lower value indicates a failed plug.
  7. If individual glow plugs appear faulty, replace the suspect plugs. If all three share high resistance, inspect harness and common feed/ground.
  8. If voltage at plug connector is correct but plug resistance is good, suspect ECU driver; test ECU output (scope recommended) and verify wiring continuity back to ECU.
  9. After repairs, clear codes and perform multiple cold start cycles to confirm the fault does not return.
  10. Safety note: Glow plug circuits carry high current; avoid shorting terminals, and use insulated tools. Allow engine to cool before removing glow plugs.

Likely causes

  • Broken wiring or corroded connector feeding glow plugs 1–3
  • One or more glow plugs for cylinders 1, 2 or 3 have failed (open or short)
  • Failed preheat/relay or blown fuse reducing supply voltage to multiple plugs
  • Poor ground at engine block or glow plug return common point
  • ECU output driver fault (less common)

Fault status

⚠️ Status
Glow plugs, cylinders 1/2/3 - circuit malfunction. ECU detects abnormal resistance/voltage/current in glow plug circuits for cylinders 1, 2 and 3. Further electrical checks required to locate fault.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5-2 hours

Similar codes

P0670 P0671 P0672 P0673 P0674 P1026
Your experience will help others
+100 karma for a short comment :)
Keep it short and practical. Up to 500 characters.
Send to email

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