U0307 — Software Incompatibility with Glow Plug Control Module

OBD2 code U0307 flags a problem with the diesel glow plug system (software incompatibility with glow plug control module). The car is usually drivable while you plan the repair. Common culprits: burned-out glow plug, blown fuse in the glow plug circuit, faulty glow plug relay or control module.

vehicle network

Is it safe to drive?

Short-term driving is OK Safe to drive once the engine is started and warmed up. The main risk is cold-weather starting: with several dead plugs the engine may not start on a cold morning. Fix before winter.

How to diagnose with an OBD scanner

Read the code and freeze frame Connect an OBD2 scanner, confirm U0307 is stored, and save the freeze frame data — it shows engine conditions when the fault was detected.
Check for companion codes and TSBs Related codes often reveal the real root cause. Also check manufacturer technical service bulletins (TSB) for your make and model — many U0xxx issues have factory fixes or software updates. Search by VIN on the manufacturer site or nhtsa.gov.
Inspect wiring and connectors Visually inspect the wiring harness and connectors related to the diesel glow plug system for damage, corrosion, chafing or poor contact.
Subsystem check Measure resistance of each glow plug — an open plug reads infinite resistance.
Subsystem check Check voltage at the glow plug rail during the pre-glow phase.
Verify the repair Clear the code, complete a full drive cycle including the conditions from the freeze frame, and confirm U0307 does not return.

Approximate repair cost

Repair cost depends on which component actually failed. Typical scenarios for U0307 (parts and labor, USD, independent shop rates): Replace one glow plug: $80–$200; Replace the glow plug relay/module: $150–$450; Replace a full set of glow plugs: $250–$600. Overall, fixing U0307 usually costs between $80 and $600. An accurate diagnosis before buying parts saves money — the most expensive scenario is rarely the first one to check.

Common questions

Will U0307 clear itself?

Sometimes U0307 clears after a few drive cycles if the fault was intermittent — for example a loose connector or a tank of bad fuel. The underlying cause usually remains, so the code tends to return. Clear it once; if it comes back, diagnose rather than erase it repeatedly.

What does OBD2 code U0307 mean?

How do I diagnose U0307 myself?

Start with a scan: confirm U0307, save the freeze frame and note any companion codes. Then inspect the wiring and connectors related to the diesel glow plug system, and verify the suspect component against live data before buying parts.

Is it safe to drive with U0307?

Safe to drive once the engine is started and warmed up. The main risk is cold-weather starting: with several dead plugs the engine may not start on a cold morning. Fix before winter.

What is the most common cause of U0307?

The most common causes are: burned-out glow plug, blown fuse in the glow plug circuit, faulty glow plug relay or control module.

What does U0307 mean?

U0307 is logged by the onboard diagnostics when the diesel glow plug system does not behave as expected. The official definition is “Software Incompatibility with Glow Plug Control Module”. This is a vehicle network category code.

The module monitors this system continuously while driving. When readings fall outside the expected range for a defined number of drive cycles, it stores U0307 and switches on the warning light. Freeze frame data saved with the code shows the exact conditions — rpm, load, temperature, speed — at the moment the fault was detected, which is the best starting point for diagnosis.

Common symptoms of U0307

rough idle until warmed up
glow plug warning light staying on
Check Engine Light on
white smoke after a cold start
hard starting in cold weather

What causes U0307?

burned-out glow plug
faulty glow plug relay or control module
blown fuse in the glow plug circuit
damaged glow plug wiring or connector

How to diagnose U0307

Connect an OBD2 scanner, confirm U0307 is stored, and save the freeze frame data — it shows engine conditions when the fault was detected.
Related codes often reveal the real root cause. Also check manufacturer technical service bulletins (TSB) for your make and model — many U0xxx issues have factory fixes or software updates. Search by VIN on the manufacturer site or nhtsa.gov.
Visually inspect the wiring harness and connectors related to the diesel glow plug system for damage, corrosion, chafing or poor contact.
Measure resistance of each glow plug — an open plug reads infinite resistance.
Check voltage at the glow plug rail during the pre-glow phase.
Clear the code, complete a full drive cycle including the conditions from the freeze frame, and confirm U0307 does not return.

How to fix U0307

Start with the cheapest and most common causes before replacing expensive parts:

Replace one glow plug — $80–$200
Replace the glow plug relay/module — $150–$450
Replace a full set of glow plugs — $250–$600

How much does it cost to fix U0307?

Repair cost depends on which component actually failed. Typical scenarios for U0307 (parts and labor, USD, independent shop rates):

Replace one glow plug: $80–$200
Replace the glow plug relay/module: $150–$450
Replace a full set of glow plugs: $250–$600

Overall, fixing U0307 usually costs between $80 and $600. An accurate diagnosis before buying parts saves money — the most expensive scenario is rarely the first one to check.

Can you drive with U0307?