Wiring fault in the glow plug circuit, such as chafed insulation causing a short to voltage; Corroded, loose or heat-damaged connector or terminal at the glow plugs or glow plug module; Faulty glow plug control module or relay, for example one stuck on or giving a wrong feedback signal; One or more failed glow plugs or a damaged glow plug supply bus bar; Low or unstable battery or charging voltage upsetting the circuit monitoring; Fault inside the engine control unit.

P1392

Glow Plug Circuit High Input Bank 1.

Mercury
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 on a Mercury means the engine control unit has detected a high input voltage in the glow plug circuit for bank 1. The control unit monitors the glow plug circuit or its feedback signal, and it saw a voltage higher than expected, which points to a short to voltage, a fault in the glow plug control stage, or a wiring fault. Which glow plugs and which module are involved depends on the model and engine.

Symptoms

Glow plug warning light on or flashing
Engine management light on
Hard starting or extended cranking when cold
White smoke and rough running after a cold start
Engine running in a reduced-function mode on some vehicles

Possible causes

Wiring fault in the glow plug circuit, such as chafed insulation causing a short to voltagelikely
Corroded, loose or heat-damaged connector or terminal at the glow plugs or glow plug modulelikely
Faulty glow plug control module or relay, for example one stuck on or giving a wrong feedback signalpossible
One or more failed glow plugs or a damaged glow plug supply bus barpossible
Low or unstable battery or charging voltage upsetting the circuit monitoringpossible
Fault inside the engine control unitrare

How to diagnose

Read all stored codes and the freeze frame data, noting engine temperature, battery voltage and whether the code is current or history.
Check the battery condition and charging voltage, since low or high voltage can affect circuit monitoring.
Visually inspect the glow plug wiring, connectors, relay and control module for damage, corrosion, heat damage or signs of rubbing.
Check the relevant fuses and relay and confirm correct operation against the manufacturer's information for that model and engine.
Measure the resistance of each glow plug and check for a short to supply or earth, comparing against the specified values.
With the circuit operating, use a multimeter or scope to check the supply and feedback voltages at the module and glow plugs, and look for a voltage that stays high when it should not.
Wiggle-test the harness while monitoring live data to find intermittent faults.
Check the wiring between the control module and the engine control unit for continuity and shorts to voltage.

How to fix

Repair or replace damaged wiring and renew any faulty connectors or terminals.
Clean and secure corroded or loose connections at the glow plugs and module.
Replace the glow plug relay or control module if it tests faulty.
Replace failed glow plugs as a set or individually as the manufacturer advises, and renew a damaged supply bus bar.
Restore the battery and charging system to good condition if voltage is the cause.

Can I keep driving?

Medium severity

The car can usually be driven short-term, but cold starting may be poor and the fault could worsen, so get it checked soon. Avoid repeated cold starts in cold weather until it is fixed, and stop if the engine runs badly or warning lights escalate.

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