P2689
Fuel Supply Heater Control Circuit High
Voltage on the fuel supply heater control line is above the expected window. The sensor heater warms the element to operating temperature (~600 °C); without it the lambda sensor stays inactive in closed loop and the ECM cannot trim mixture.
- Check engine light: Yes
- Emissions related: No
- Repair difficulty: medium
Common causes
Ordered by how often each turns out to be the cause.
- Control wire shorted to B+Common
- Open relay coilPossible
- Connector pins corroded - high contact resistanceLess likely
Parts involved
- Fuel Supply Heater
- Wiring Harness
P2689 is a generic OBD-II code defined by SAE J2012. Exact wording and diagnostic procedure vary by manufacturer and model. Code definitions are drawn from the public-domain OBDex dataset; the workshop notes are our own.