What it means
The controller detects voltage above the expected range in the fuel supply heater control circuit. This code concerns the fuel heater, not an oxygen sensor heater.
At a glance
- Usually lights the check-engine light
How it works
The fuel supply heater warms diesel near the filter or supply line to help prevent cold-weather waxing. The control module monitors circuit voltage while commanding the heater. P2689 sets when voltage is higher than expected; an control wire short to battery voltage, an open relay coil, or a poor corroded connection can cause this condition.
Common causes
Most likely first.
- Control wire shorted to B+
- Open relay coil
- Connector pins corroded - high contact resistance
Symptoms
- Check-engine light
- Hard starting in cold weather
- Poor running in cold weather
How to diagnose it
- Review freeze-frame data and heater command history, if available, to establish whether the high-voltage reading occurred while the heater was being controlled.
- Inspect the fuel heater control wire for damaged insulation or contact with a battery-positive feed, and check connectors for corrosion or loose pins.
- Check whether the relay is seated and test its coil for an open circuit using the manufacturer's procedure.
- With the circuit isolated as directed by the manufacturer, test the control wire for a short to battery voltage.
- Check voltage at the heater control circuit and across suspect connector contacts, comparing readings with the manufacturer's specification.
Common fixes
- Repair a control wire shorted to battery voltage.
- Clean or repair corroded, loose connector terminals.
- Replace a relay with an open coil.
- Repair the affected circuit connection, then clear the code and verify that voltage follows the heater command.
Can I keep driving?
If the engine runs normally, drive cautiously and avoid cold-weather trips until the heater circuit is checked. The heater may not warm the fuel, which can allow waxing to restrict flow and cause hard starting or poor running.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.