What it means
The glow plug controller and the engine ECU run incompatible software versions. Cold-start preheating may be inhibited and the glow plug warning lamp can stay on.
At a glance
- Usually lights the warning light of the system that lost communication
How it works
The glow plug control module manages preheating on a diesel engine and communicates its software identity and status to the engine ECU. U0307 sets when the ECU and glow plug module report incompatible software versions or configuration. A mismatched flash or replacement can cause the fault; network routing problems can also prevent the expected module data from reaching the ECU.
Common causes
Most likely first.
- Software flash mismatch after parts swap
- Gateway module routing CAN messages incorrectly
- CAN terminating resistor (120 Ω) drifted out of spec
Symptoms
- Multiple warning lights may illuminate
- Affected modules may go into limp mode or shut down
- Specific functions inoperative depending on module
- Diagnostic tools may show communication faults
How to diagnose it
- Scan the engine ECU and glow plug control module for U0307 and related communication or glow plug codes, and save freeze-frame data.
- Check live data for glow plug module communication and preheat command, and note whether the fault is most evident during cold starts.
- Review service history for a glow plug module replacement or interrupted software update.
- Compare the module's software and calibration identifiers with the engine ECU's required configuration using a capable scan tool.
- If the identifiers appear compatible but communication still fails, inspect connectors and test network wiring or gateway routing using the manufacturer's procedure.
Common fixes
- Complete or repeat an interrupted glow plug module update with the correct calibration.
- Correct coding or configuration so the glow plug module matches the engine ECU.
- Repair a poor connector or network wiring fault affecting module communication.
- Program or replace the glow plug control module if it remains incompatible after wiring and configuration are confirmed.
Can I keep driving?
The vehicle may still run, but cold starts can become difficult and the engine may run poorly while cold; avoid repeated extended cranking. If the engine is rough, produces heavy smoke, or has reduced power, limit driving and have the fault addressed promptly.
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.