Failed glow plug on bank 2 (short internally or to ground); Chafed or shorted glow plug wiring harness on bank 2; Corroded or loose glow plug connector causing high resistance; Faulty glow plug control module (GPCM) internal short; PCM driver circuit fault for bank 2 glow plug control; Moisture intrusion in the glow plug circuit connectors

DTC codes / Ford codes / P1393

P1393 · FordGlow Plug Circuit Low Input Bank 2

Q: What does code P1393 mean?

Glow Plug Circuit Low Input Bank 2. The powertrain control module (PCM) monitors the glow plug circuit for bank 2 and detects a low input voltage, meaning the circuit is drawing excessive current or the voltage signal is below the expected threshold. This typically indicates a short to ground, a failed glow plug, or a wiring fault in the bank 2 glow plug circuit, which can prevent proper cold-start glow plug operation.

The powertrain control module (PCM) monitors the glow plug circuit for bank 2 and detects a low input voltage, meaning the circuit is drawing excessive current or the voltage signal is below the expected threshold. This typically indicates a short to ground, a failed glow plug, or a wiring fault in the bank 2 glow plug circuit, which can prevent proper cold-start glow plug operation.

SystemPowertrain

Code typeFord specific

SeverityMedium

Fix difficultyIntermediate

AreaIgnition system and misfire

Symptoms you may notice

Illuminated check engine light or glow plug warning lamp
Hard starting or rough idle when the engine is cold
Excessive white smoke from the exhaust after a cold start
Reduced engine performance and poor fuel economy during warm-up
Often no symptoms besides the warning light, especially in mild weather

Common causes, most likely first

Failed glow plug on bank 2 (short internally or to ground)
Chafed or shorted glow plug wiring harness on bank 2
Corroded or loose glow plug connector causing high resistance
Faulty glow plug control module (GPCM) internal short
PCM driver circuit fault for bank 2 glow plug control
Moisture intrusion in the glow plug circuit connectors

How to diagnose and fix it

Scan all modules for related codes and record freeze-frame data to confirm the fault conditions
Visually inspect bank 2 glow plug harness and connectors for chafing, corrosion, or loose pins
Measure resistance of each bank 2 glow plug and compare to specification to identify a shorted plug
Disconnect the glow plug control module and check for short to ground on the bank 2 control circuit
Test the glow plug control module operation with a bidirectional scan tool or by back-probing the circuit
Repair or replace the faulty glow plug, harness section, or control module as diagnosed
Clear codes and perform a cold-start verification to confirm the repair

What Ford techs check before replacing glow plugs

A low input code often results from a shorted glow plug rather than an open circuit, so resistance testing each plug is critical before condemning the control module.
The glow plug control module on Ford diesels can set a bank-specific low input code even when the fault lies in the shared power or ground circuit, so check those connections first.
Chafed harness sections near the valve cover or exhaust manifold are a common hidden cause that visual inspection from above may miss.
This code can be set by a weak battery or charging system issue that causes low voltage during glow plug operation, so verify battery health before parts replacement.
After repairs, some Ford models require a glow plug adaptation reset or a drive cycle to clear the code permanently.

Can I keep driving with P1393?

You can usually drive the vehicle, but cold starting may be difficult and extended driving with a faulty glow plug circuit can lead to misfires and increased emissions. Avoid heavy loads or long idling until the fault is repaired, and address it promptly to prevent further damage to the glow plug control system.

Tools that help

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Guidance is general and written for Ford vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.