P064C — Glow Plug Control Module

powertrain (engine/transmission)

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 P064C 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 P0xxx 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 P064C does not return.

Approximate repair cost

Repair cost depends on which component actually failed. Typical scenarios for P064C (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 P064C 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

Is it safe to drive with P064C?

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 do I diagnose P064C myself?

Start with a scan: confirm P064C, 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.

Will P064C clear itself?

Sometimes P064C 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 is the most common cause of P064C?

The most common causes are: corroded glow plug connectors, blown fuse in the glow plug circuit, burned-out glow plug.

How much does it cost to fix P064C?

Replace one glow plug — $80–$200; Replace the glow plug relay/module — $150–$450; Replace a full set of glow plugs — $250–$600. Exact cost depends on the root cause, your vehicle and local labor rates — a proper diagnosis is the cheapest first step.

When your engine control module logs trouble code P064C, it's telling you that something has gone wrong inside the diesel glow plug control circuit. This is a powertrain-related OBD2 code, which means it falls under the engine and transmission management system. The PCM doesn't log P064C after a single bad reading — it watches for the same fault condition to occur repeatedly under specific operating conditions before it triggers the check engine light. That's important to know because it tells you the problem isn't a one-off sensor glitch; something genuine has failed in the glow plug system.

Diesel engines rely on glow plugs to heat the combustion chambers before and during cold starts. The glow plug control module manages power delivery to all the plugs, turning them on and off according to engine temperature and startup demands. When the module detects an open circuit, a dead plug, or a wiring failure in this system, it sets P064C. The stored freeze frame data captures engine load, RPM, coolant temperature, and vehicle speed at the exact moment the fault occurred — use that information to reproduce the failure conditions during your diagnosis.

Once P064C is active, you'll likely notice the problem before you even scan the code. White smoke billowing from the tailpipe on cold mornings is one of the most common clues, caused by unburned fuel that can't ignite properly without preheated chambers. The glow plug warning light on your dashboard may stay illuminated, and the check engine light will follow. Cold starts become sluggish or fail entirely, and the engine may run rough with a pronounced shake until it reaches operating temperature.

What triggers P064C?

Several different failures can cause the control module to flag this code. In most cases the culprit is one or more burned-out glow plugs — these heating elements have a limited service life and eventually open up internally. A failed glow plug relay or the control module itself can also throw the system offline. Wiring damage ranks high on the list too: chafed insulation, broken strands inside the harness, and corroded or loose connectors at the glow plug rail create high resistance that the module interprets as a fault. Don't overlook a blown fuse in the glow plug circuit either — it happens more often than people expect and produces the same result.

Symptoms of P064C

Noticeable white exhaust smoke during cold starts
Glow plug indicator light remains illuminated after startup
Check Engine Light turns on and stays on
Engine cranks slowly or refuses to start in cold temperatures
Rough, unstable idle that smooths out once the engine reaches normal operating temperature

Diagnosing P064C

Start by connecting a quality OBD2 scanner and confirm that P064C is stored in the PCM. Save the freeze frame data immediately — it documents engine load, RPM, temperature, and vehicle speed at the moment of failure. Those parameters are your roadmap for recreating the fault during testing.

Next, check for any related diagnostic trouble codes. Coexisting codes often point directly to the root cause, whether it's a specific cylinder or a problem in the control circuit. While you're researching, pull up any manufacturer TSBs for your make and model — the factory may have released a software update or known fix for this specific code family.

Perform a thorough visual inspection of the glow plug wiring harness and connectors. Look for damaged insulation, melted wires near hot engine components, corrosion buildup on the terminals, and any connectors that aren't fully seated. Even minor issues here can cause the module to flag a fault.

Measure the resistance of each glow plug individually using a multimeter. A functioning plug typically reads between 0.5 and 2 ohms depending on the application. An open circuit showing infinite resistance confirms that plug is dead and needs replacement. Also check for battery voltage at the glow plug bus bar during the pre-glow cycle — no voltage means the control module isn't activating the system at all.

After addressing whatever you find, clear the code and complete a full drive cycle that includes the exact conditions recorded in the freeze frame. If P064C doesn't return, the repair is confirmed.

Repair options and costs

Address the least expensive likely causes before spending money on major components. If testing reveals a single failed glow plug, one replacement runs between $80 and $200 depending on the brand and labor time. When the glow plug relay or the control module itself is faulty, expect to pay $150 to $450 for the part plus installation. Replacing all glow plugs as a set — common practice when multiple plugs show problems or when you're already in the area — typically costs $250 to $600 total.

Total repair cost

P064C repair typically falls somewhere between $80 and $600 depending on which component fails. The single-plug scenario is the most affordable fix, while a full set replacement or module replacement sits at the higher end. Skipping the diagnostic step and replacing parts randomly is how repair bills balloon — the problem is usually simpler than it appears.

Can you keep driving with P064C?

Once the engine warms up, operation is generally safe and the vehicle drives normally. The real concern is cold weather: if multiple glow plugs are dead, the engine may not start on a cold morning at all, or it will run poorly until everything heats up. Don't wait until winter to address this code — get it diagnosed and repaired before cold weather arrives.