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P1392

Glow Plug Circuit High Input (Bank #1).

  • Other
  • Powertrain
  • Manufacturer code
  • Medium severity

How this code is built

P
SystemPowertrain
1
Defined byThe manufacturer
3
AreaIgnition system or misfire
92
FaultThe specific fault in that area

What it means

P1392 is generally defined as Glow Plug Circuit High Input on Bank 1, and it applies to diesel engines. The engine control unit monitors the voltage or feedback signal in the glow plug circuit and saw a reading higher than expected, which points to a short to voltage or a fault in the driver or relay. The exact circuit layout and test values depend on the make, model and engine, and this code means something different on other makes, so confirm the definition for the vehicle in front of you.

Symptoms

  • Engine management warning light on
  • Hard starting or extended cranking when cold
  • White or grey smoke on cold start-up
  • Rough running or misfire until the engine warms up
  • Glow plug warning light behaving oddly, such as staying on, flashing or not lighting
  • Glow plugs not operating or staying on too long

Possible causes

  • Wiring fault in the bank 1 glow plug circuit, such as a short to voltage or chafed insulationlikely
  • Faulty glow plug control module or relay, for example a stuck-on or failed output driverlikely
  • Corroded or loose connectors at the glow plugs, relay or module, giving a false high signalpossible
  • Failed or shorted glow plug on bank 1possible
  • Poor earth connection or unstable supply voltage affecting the circuit feedback signalpossible
  • Fault inside the engine control unitrare

How to diagnose

  1. Read all stored and pending codes and note the freeze frame data, especially coolant and ambient temperature and battery voltage
  2. Check battery condition and charging voltage, as low or unstable voltage can upset glow plug circuit readings
  3. Visually inspect the glow plug wiring, relay, module and connectors on bank 1 for heat damage, chafing, corrosion and loose pins
  4. Use live data to see glow plug commanded state and any feedback, and check whether it matches actual operation
  5. Measure glow plug resistance and current draw against the manufacturer's specification, as values vary by engine
  6. Check the supply and earth to the relay or module, and test the circuit for a short to voltage with the ignition on and the module unplugged
  7. Test the relay or glow plug module output using the manufacturer's procedure
  8. If everything else checks out, check for software updates or known faults for the specific model before suspecting the control unit

How to fix

  • Repair or replace damaged wiring and clean or replace corroded connectors
  • Replace any failed glow plugs, as a set if the engine's service guidance recommends it
  • Replace a faulty glow plug relay or control module
  • Restore proper power and earth connections and correct any battery or charging problems
  • Update the control unit software only if a known fault or outdated calibration is documented for that model, and replace the control unit as a last resort

Can I keep driving?

Medium severity

The car can usually be driven, but cold starting may be poor and the fault may get worse, so get it checked soon. Avoid repeated cold starts and long cranking, and stop driving if the engine runs very roughly or the wiring smells hot.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.

This code for other makes

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