P0679 Code: Meaning, Symptoms, Causes & Fix

Overview

P0679 is triggered when monitoring logic identifies an issue with Cylinder 9 Glow Plug Circuit affecting powertrain controls.

Symptoms

rough operation in certain conditions
check engine light
increased fuel use

Common causes

Open circuit in wiring affecting cylinder 9 glow plug circuit
Disconnected or loose connector
Connector pin damage/corrosion or harness stress near related components

How to diagnose P0679

Confirm P0679 and capture freeze-frame data with a professional scan tool.
Inspect wiring, connectors, and grounds related to cylinder 9 glow plug circuit for obvious defects.
Use a continuity test from module pin to component to identify opens/high resistance.
Check for related DTCs to identify the root-cause chain before replacing parts.
After repair, clear codes and confirm readiness monitors complete without recurrence.

Severity of code P0679

Moderate: This code is moderate severity: the vehicle may still operate, but fault progression can increase repair cost over time.

Can you drive with P0679?

Most vehicles can be driven short-term with P0679, but postpone heavy load/highway driving until repaired.

If the warning lamp is flashing or drivability/safety is affected, avoid driving and diagnose immediately.

How to fix it (step-by-step)

Repair obvious wiring/connector faults first to prevent repeat parts replacement.
Address the root fault mode (open) in the cylinder 9 glow plug circuit circuit/system.
Apply the required relearn/adaptation procedure if specified by service information.
Road-test and verify P0679 remains cleared under the conditions that originally set the code.

Fix options

Clear corrosion and protect terminals.
Repair open circuit and secure connector lock.
Clear DTCs and verify with live data and completed drive cycle.

Typical repair cost

$200-$900

Common mistakes when diagnosing P0679

Replacing parts without verifying voltage, ground, and signal integrity first.
Ignoring related stored/pending codes that indicate upstream faults.
Skipping post-repair verification drive cycle and readiness checks.

P0679 in common vehicles

P0679 appears across makes such as Ford, Toyota, Honda, Chevrolet. Failure patterns differ by platform: wiring routes, software calibration, and component supplier revisions can change root cause.

Frequently asked questions

What causes P0679?

P0679 is commonly set by open faults affecting cylinder 9 glow plug circuit.

How much does it cost to fix P0679?

For P0679, repair costs are typically $200-$900 depending on exact root cause, labor rates, and part quality.

Can I clear P0679 without repair?

You can clear P0679 temporarily, but the code usually returns until the underlying fault is corrected.