The P0382 code means the powertrain control module detected an electrical malfunction in diesel Glow Plug/Heater Circuit “B.”
Circuit “B” may power a second group of glow plugs, a separate cylinder bank or another output channel from the glow-plug controller. Its exact layout varies by manufacturer, so “B” should not automatically be translated into Bank 2.
Common causes include failed glow plugs within the Circuit “B” group, a damaged fuse or fusible link, burned controller contacts, a corroded bus bar, high-resistance wiring or a defective controller output.
P0382 Quick Reference
| Item | Details |
|---|---|
| Code | P0382 |
| Definition | Glow Plug/Heater Circuit “B” Malfunction |
| System | Diesel cold-start heating |
| Primary fault | Electrical malfunction in Heater Circuit “B” |
| Common causes | Failed glow plug, fuse, controller channel, bus bar or wiring |
| Common symptoms | Hard cold starting, rough cold idle or white smoke |
| Severity | Moderate |
| Safe to drive? | Usually, if the engine starts and runs normally |
| Best diagnostic tools | Scan tool, multimeter and current clamp |
For additional definitions, visit the complete P-series OBD-II code list or browse the Pro Street OBD-II Doctor.
What Does the P0382 Code Mean?
P0382 is stored when the PCM or glow-plug controller detects an electrical problem in Heater Circuit “B.”
The controller may monitor:
- Circuit “B” voltage
- Group current draw
- Individual glow-plug current
- Controller output feedback
- Open- or short-circuit conditions
- Commanded versus actual operation
- Voltage drop through the shared feed
- Heating time
- Current balance between Circuits “A” and “B”
If Circuit “B” draws too little current, too much current or fails to respond when commanded, the PCM may store P0382.
What Does Circuit “B” Identify?
Circuit “B” does not have one universal layout.
Depending on the vehicle, it may identify:
- One cylinder bank
- The second half of the engine
- A group of selected cylinders
- A separate controller output
- A second bus bar
- A secondary intake-air heater
- Another manufacturer-defined heater channel
Never identify the affected cylinders by guessing. Use the vehicle’s wiring diagram and connector information.
For example, one manufacturer may divide an eight-cylinder diesel into two groups of four. Another may divide the circuit according to controller-driver channels rather than physical cylinder banks.
Apparently “Circuit B” was considered more helpful than simply listing the affected cylinders.
What Do Diesel Glow Plugs Do?
Diesel engines ignite fuel using compression heat rather than conventional spark plugs.
During cold starts, the cylinder walls and combustion chambers absorb heat. Glow plugs raise the temperature near the combustion area so injected fuel can ignite more reliably.
Glow plugs may operate during:
- Cold preheating
- Engine cranking
- Initial idle
- Post-start warm-up
- Cold-weather driving
- Emissions-control strategies
Modern systems may continue operating the glow plugs after the dashboard indicator turns off. This after-glow period can improve idle quality and reduce cold-start smoke.
How Heater Circuit “B” Works
A divided glow-plug system may contain:
- Battery
- High-amperage fuse or fusible link
- Glow-plug control module
- Circuit “A” output
- Circuit “B” output
- Separate power cables
- Separate bus bars or wiring groups
- Individual glow plugs
- Engine ground
- PCM command and feedback circuits
When heating is required, the controller activates both circuit groups according to engine temperature and operating conditions.
The controller may compare current draw between Circuits “A” and “B.” If Circuit “A” draws normally but Circuit “B” does not, the difference helps isolate the fault.
Common P0382 Symptoms
Symptoms are usually most noticeable when the engine is cold.
Common symptoms include:
- Illuminated Check Engine Light
- Glow-plug warning light
- Extended cold cranking
- Difficult cold starting
- Intermittent cold no-start
- Rough idle after starting
- Temporary cylinder misfires
- White exhaust smoke
- Excessive diesel odor
- Reduced cold-start performance
- Increased cold-start emissions
- Engine runs normally after warming up
If only part of the glow-plug system has failed, the engine may still start but run roughly until heat builds inside the affected cylinders.
For broader starting problems, see Engine Cranks but Won’t Start: Common Causes.
Common Causes of P0382
Possible causes include:
- One or more failed glow plugs in Circuit “B”
- Open glow-plug heating element
- Internally shorted glow plug
- Incorrect replacement glow plug
- Blown Circuit “B” fuse
- Failed fusible link
- Faulty Circuit “B” relay
- Failed glow-plug controller output
- Burned controller terminal
- Corroded Circuit “B” bus bar
- Loose bus-bar connection
- Open Circuit “B” power cable
- High resistance in the shared feed
- Damaged glow-plug wiring
- Short to ground
- Short to voltage
- Loose connector terminal
- Water or oil contamination
- Poor engine ground
- Weak battery
- Low charging voltage
- Incorrect temperature-sensor input
- PCM connector damage
- PCM software problem
- Internal PCM failure
A single failed glow plug may set P0382 if the controller monitors total current for the entire Circuit “B” group.
How Serious Is P0382?
P0382 is normally a moderate-severity code.
The vehicle may run normally after warming up, but ignoring the fault can lead to:
- Increasingly difficult cold starts
- Battery discharge
- Starter wear
- Heavy white smoke
- Rough cold operation
- Complete no-start in low temperatures
- Increased emissions
- Electrical overheating if the circuit is shorted
Inspect the system promptly if you notice melted connectors, burning odors, smoke or excessive heat near the controller or bus bar.
P0382 Compared With Related Codes
| Code | Meaning | Diagnostic focus |
| P0380 | Glow Plug/Heater Circuit “A” | Heater Circuit “A” electrical fault |
| P0381 | Glow Plug/Heater Indicator Circuit | Wait-to-start light or display |
| P0382 | Glow Plug/Heater Circuit “B” | Heater Circuit “B” electrical fault |
| P0670 | Glow Plug Control Module Circuit | Controller command or module circuit |
| P0671–P0678 | Cylinder-Specific Glow Plug Circuit | Individual cylinder glow-plug fault |
P0382 should remain focused on the grouped Heater Circuit “B” path.
P0382 Versus P0380
P0380 and P0382 describe similar faults on different heater circuits:
- P0380 applies to Circuit “A.”
- P0382 applies to Circuit “B.”
The two circuits may have separate:
- Controller outputs
- Fuses
- Feed cables
- Bus bars
- Connector terminals
- Glow-plug groups
Comparing the two circuits can provide a useful diagnostic baseline.
P0382 Versus P0381
P0381 concerns the dashboard glow-plug or wait-to-start indicator.
P0382 concerns the high-current heater circuit that powers a group of glow plugs.
A functioning dashboard indicator does not prove Circuit “B” is delivering current.
P0382 Versus P0670
P0670 concerns the control-module circuit.
A failed module may cause P0382 if its Circuit “B” output stops working, but the code may also result from downstream wiring, bus-bar or glow-plug faults.
How to Diagnose the P0382 Code
1. Scan All Modules
Connect a capable scan tool and record:
- Stored codes
- Pending codes
- Freeze-frame data
- Coolant temperature
- Intake-air temperature
- Battery voltage
- Glow-plug command
- Circuit “A” current
- Circuit “B” current
- Individual glow-plug current, when supported
- Controller feedback
- Related cylinder-specific codes
Do not clear the codes before saving this information.
A code identifying one cylinder within the Circuit “B” group may provide an immediate diagnostic direction.
2. Identify the Circuit “B” Layout
Consult the correct wiring diagram and determine:
- Which cylinders belong to Circuit “B”
- Which controller terminal operates it
- Whether it has a separate fuse
- Whether it uses a separate relay
- Which bus bar or power cable feeds it
- Whether current is monitored by group or individually
- Ground locations
- Connector pin assignments
Do not assume Circuit “B” equals Bank 2 unless the manufacturer specifically defines it that way.
3. Compare Circuits “A” and “B”
Use scan data and physical measurements to compare the two circuits.
Check:
- Commanded state
- Output voltage
- Total current draw
- Voltage drop
- Heating duration
- Temperature behavior
- Number of connected glow plugs
If Circuit “A” works normally, it provides a useful comparison for Circuit “B.”
Account for different numbers or types of glow plugs before assuming the current readings should be identical.
4. Test the Battery and Starting System
Glow plugs and the starter place heavy demand on the battery.
Test:
- Battery state of charge
- Battery load capacity
- Cranking voltage
- Starter current draw
- Positive-cable voltage drop
- Ground-cable voltage drop
- Alternator output
- Engine grounds
Correct low voltage before evaluating glow-plug current.
5. Inspect the Circuit “B” Fuse
Locate the correct fuse or fusible link.
Check for:
- Open fuse
- Heat damage
- Loose terminals
- Corrosion
- Melted fuse holder
- Voltage on both sides
- Voltage drop under load
If the fuse has blown, locate the short or excessive-current condition before replacing it.
Installing a larger fuse converts a diagnostic problem into a wiring-harness toaster.
6. Inspect the Controller and Relay
Inspect the glow-plug controller or Circuit “B” relay for:
- Melted housing
- Burned terminals
- Loose cables
- Water intrusion
- Corrosion
- Heat discoloration
- Damaged connector locks
- Correct command signal
Verify that the controller receives battery power and produces a Circuit “B” output when commanded.
A relay may click while its internal contacts remain too resistive to carry glow-plug current.
7. Inspect the Circuit “B” Bus Bar and Wiring
Inspect the entire grouped feed.
Look for:
- Corroded bus bar
- Loose fasteners
- Broken connections
- Burned terminals
- Damaged insulation
- Chafed wires
- Oil contamination
- Missing protective boots
- Poor previous repairs
- Heat damage
Disconnect power according to manufacturer procedures before servicing high-amperage connections.
8. Check Circuit “B” Output Voltage
Command the glow-plug system with a bidirectional scan tool when supported.
Measure voltage at:
- Controller input
- Circuit “B” controller output
- Bus-bar input
- Individual glow-plug terminals
Compare the readings with Circuit “A” and manufacturer specifications.
Normal controller voltage with low bus-bar voltage indicates excessive resistance between those points.
9. Perform a Voltage-Drop Test
Measure voltage drop across:
- Battery to controller
- Circuit “B” fuse
- Relay contacts
- Controller output
- Shared feed cable
- Bus-bar connections
- Engine ground
Voltage-drop testing should be performed while the circuit carries current.
An unloaded continuity test may pass even when a connection becomes highly resistive under glow-plug load.
10. Measure Circuit “B” Current
Use a properly rated inductive current clamp around the Circuit “B” feed.
Observe:
- Initial current
- Current reduction as the plugs heat
- Current stability
- Total current relative to specifications
- Difference between Circuits “A” and “B”
Low current may indicate:
- One or more open glow plugs
- High circuit resistance
- Low supply voltage
- Failed relay contacts
- Partial controller-output failure
Excessive current may indicate a shorted glow plug or wiring fault.
11. Compare Individual Glow-Plug Current
When supported, use scan data or an appropriate current clamp to compare individual glow plugs within Circuit “B.”
A plug drawing substantially less current may be open or highly resistive.
A plug drawing excessive current may be shorted internally.
Testing individual current can identify the defective plug without removing every glow plug from the cylinder head.
12. Test Glow-Plug Resistance Carefully
Disconnect the Circuit “B” plugs according to the service procedure.
Because glow plugs have low resistance:
- Short the meter leads together.
- Record or zero lead resistance.
- Measure each glow plug.
- Compare the plugs with one another.
- Compare results with manufacturer specifications.
An open reading normally indicates a failed heating element.
Do not use one generic resistance specification for every diesel engine. Modern glow plugs vary in design and operating voltage.
13. Do Not Apply Battery Voltage Blindly
Modern fast-heating, low-voltage or pressure-sensing glow plugs can be damaged by direct battery voltage.
Only perform a direct-power test when manufacturer information specifies:
- Correct test voltage
- Maximum duration
- Current limit
- Approved grounding method
Otherwise, use resistance, current and controller-output testing.
14. Inspect Removed Glow Plugs
If removal is required, inspect for:
- Swollen tips
- Cracked heating elements
- Carbon buildup
- Erosion
- Melted tips
- Oil contamination
- Incorrect part number
Use the specified removal method and torque. A seized glow plug can break inside the cylinder head, which is the automotive equivalent of a small problem filing for a major promotion.
15. Test the Controller Inputs
If Circuit “B” wiring and glow plugs pass testing, verify:
- Controller battery power
- Ignition power
- Ground circuits
- PCM command
- Temperature inputs
- Feedback circuits
- Network communication
If Circuit “A” operates but Circuit “B” does not, an internal Circuit “B” output-driver failure becomes more likely.
16. Evaluate the PCM Last
Consider PCM failure only after verifying:
- Battery condition
- Circuit “B” fuse
- Controller operation
- Bus-bar condition
- Glow-plug resistance
- Group current draw
- Voltage drop
- Temperature inputs
- Network communication
- Applicable software updates
PCM replacement should be supported by circuit testing, not by the fact that everything else was easier to reach.
Common P0382 Diagnostic Mistakes
Assuming Circuit “B” Means Bank 2
Circuit assignments vary. Use the wiring diagram to identify the actual glow-plug group.
Replacing Every Glow Plug Immediately
P0382 may be caused by a fuse, controller channel, bus bar or shared wiring problem.
Testing Resistance Without Accounting for Meter Leads
Lead resistance can substantially distort low-ohm glow-plug measurements.
Ignoring Circuit “A”
A working Circuit “A” provides useful comparison data for voltage, current and controller behavior.
Assuming a Clicking Relay Is Functional
Relay contacts can be burned even when the relay coil clicks.
Replacing a Blown Fuse Without Finding the Cause
A shorted plug or cable may immediately blow the replacement.
Applying 12 Volts to Modern Glow Plugs
Some modern plugs operate below system voltage or contain pressure sensors. Direct battery power may destroy them.
Common P0382 Repairs
Possible repairs include:
- Replacing failed Circuit “B” glow plugs
- Installing the correct glow-plug type
- Replacing a fuse after repairing the cause
- Replacing a damaged fusible link
- Replacing the Circuit “B” relay
- Replacing or repairing the glow-plug controller
- Cleaning or replacing the Circuit “B” bus bar
- Repairing burned controller terminals
- Repairing high-resistance wiring
- Repairing a short to ground
- Repairing Circuit “B” power or ground
- Replacing a weak battery
- Repairing incorrect temperature inputs
- Updating controller or PCM software
- Replacing and programming a confirmed defective module
Estimated P0382 Repair Costs
| Repair | Estimated cost |
| Diagnostic testing | $100–$250 |
| Fuse, terminal or wiring repair | $75–$400 |
| Single glow-plug replacement | $150–$400 |
| Circuit “B” glow-plug group | $250–$800 |
| Complete glow-plug set | $350–$1,200 |
| Glow-plug relay replacement | $150–$500 |
| Bus-bar replacement | $150–$450 |
| Glow-plug controller replacement | $300–$1,200 |
| Broken glow-plug extraction | $500–$2,500+ |
| PCM replacement and programming | $700–$2,000+ |
Actual costs depend on the number of affected glow plugs and their accessibility.
Can You Drive With P0382?
A diesel vehicle can usually be driven with P0382 if it starts normally and runs smoothly.
However, continued operation may lead to:
- Increasingly difficult cold starts
- Extended cranking
- Battery discharge
- Starter wear
- Rough cold idle
- White smoke
- Complete no-start in colder weather
Do not drive if the controller, fuse block, bus bar or wiring shows melting, smoke, electrical odor or excessive heat.
Can P0382 Cause White Smoke?
Yes. If the Circuit “B” glow-plug group does not heat correctly, fuel in those cylinders may not burn completely during a cold start.
That can produce temporary white smoke, rough idle and diesel odor.
White smoke that continues after warm-up may indicate other problems. See White Smoke From Exhaust: Causes and Warning Signs for broader diagnosis.
How to Verify the Repair
After completing the repair:
- Fully charge the battery.
- Clear stored and pending codes.
- Allow the engine to cool.
- Verify temperature-sensor readings.
- Command the glow-plug system.
- Measure Circuit “B” output voltage.
- Measure Circuit “B” current.
- Compare Circuits “A” and “B.”
- Verify current reaches each affected plug.
- Start the engine cold.
- Check idle quality and exhaust smoke.
- Rescan for pending codes.
- Inspect repaired terminals for abnormal heat.
A successful repair restores proper voltage, current draw and reliable cold-start operation to Circuit “B.”
P0382 Frequently Asked Questions
What does the P0382 code mean?
P0382 means the PCM detected a malfunction in diesel Glow Plug/Heater Circuit “B.”
Does Circuit “B” mean Bank 2?
Not necessarily. Circuit “B” may represent a bank, cylinder group, bus bar or controller-output channel defined by the manufacturer.
What commonly causes P0382?
Common causes include failed glow plugs, a blown fuse, a faulty relay or controller channel, corroded bus-bar connections and damaged wiring.
Can P0382 prevent a diesel engine from starting?
Yes, especially in cold weather. Failure of an entire glow-plug group can make cold ignition difficult or impossible.
Can a weak battery cause P0382?
Yes. Low battery voltage can reduce glow-plug current and affect controller operation.
Is P0382 always caused by bad glow plugs?
No. Shared Circuit “B” components such as the fuse, controller output, bus bar and wiring can also cause the code.
What is the difference between P0380 and P0382?
P0380 applies to Heater Circuit “A.” P0382 applies to Heater Circuit “B.”
What is the difference between P0381 and P0382?
P0381 concerns the dashboard glow-plug indicator. P0382 concerns a high-current glow-plug heater circuit.
Should all Circuit “B” glow plugs be replaced together?
Not automatically. Test each plug and consider age, accessibility and manufacturer recommendations before replacing the entire group.
Final Thoughts
P0382 identifies an electrical malfunction in Glow Plug/Heater Circuit “B.” The affected circuit may represent a cylinder bank, glow-plug group or controller-output channel.
Identify the actual Circuit “B” layout first. Then compare its voltage, current draw and voltage drop with Circuit “A.”
That comparison helps separate failed glow plugs from a fuse, controller, bus-bar or wiring problem. It also prevents “Circuit B probably means the right side” from becoming the most expensive sentence in the repair order.
For more diagnostic coverage, visit the Pro Street OBD-II Doctor and the complete P-series OBD-II code index.
