OBD-II Diagnostic Trouble Code
P0382 — Glow Plug/Heater Circuit A Range/Performance
P0382 means glow plug or heater circuit A is working, but its current, voltage or response is outside the expected range. On many engines it signals a partial failure, such as one or more weak glow plugs or a relay not supplying full power. Some OEMs define P0382 as glow plug circuit B instead, so confirm the definition in service information.
Severity 2/5
Truck-relevant
Service soon
Severity
Service soon
Glow Plug/Heater Circuit A Range/Performance
Code
P0382
Category
Powertrain
Subsystem
Cold Start
Truck-relevant
Yes
What this means for truckers
P0382 (Glow Plug/Heater Circuit A Range/Performance) — variant of P0670 with more specific diagnostic criteria. Same fix path: test glow plug control module and glow plug resistance.
Before you replace parts — try this first
P0382 on the Cold Start system is most often one or more glow plugs failing or drawing incorrect current — not a dead part. On commercial diesels especially, work these in order before spending money on parts:
- Confirm the symptoms. Match what your truck is doing to the Symptoms section below. If the code is set but the symptoms are not there, clear the code and re-test after a drive cycle — it may not return.
- Clean and dry the sensor connector. Water, road salt, or oil seeping into a connector is the #1 fake sensor failure. Disconnect, look for green corrosion or moisture, spray with electrical contact cleaner, dry, reseat. Many faults clear here for $0.
- Inspect the wiring harness. Trace the wire from the sensor toward the ECM — look for chafing against the engine block, melted insulation near the turbo or exhaust, or pinch points where a clamp has rubbed through.
- Test the sensor before swapping it. Most Common Causes (below) list the expected voltage or resistance range — a $20 multimeter saves a $300 sensor swap that does not fix the problem.
- Only then, replace the part. Use the OEM or a tier-1 aftermarket. Cheap sensors throw the same code in two weeks.
Symptoms
Hard cold starts, longer cranking, rough running and white smoke for the first minutes after a cold start. In warm weather there may be only a check-engine light.
Common causes
- CommonOne or more glow plugs failing or drawing incorrect current ($200–$900)
- CommonWeak glow plug relay or control module output ($200–$700)
- OccasionalHigh resistance from corroded connectors or loose power feed ($100–$400)
- OccasionalLow battery voltage or poor charging during preheat ($150–$700)
How to fix
Check battery state and voltage at the glow plug feed during preheat
When to use: First step
Measure each glow plug's resistance or current and replace weak plugs
When to use: When supply voltage is good
Test the relay or control module output under load
When to use: When the plugs test good
Clean or repair corroded connectors and terminals
When to use: When voltage drop is found in the circuit
Affects most
No specific vehicle pattern found in our complaint database. This code can appear on any vehicle that supports OBD-II diagnostics.
Related
- → Browse all DTC trouble codes
- → Decode a VIN to check codes for your truck
- → Owner-operator maintenance guides
- → P0300 — Random/Multiple Cylinder Misfire Detected
- → P0301 — Cylinder 1 Misfire Detected
- → P0302 — Cylinder 2 Misfire Detected
- → P0303 — Cylinder 3 Misfire Detected
- → P0304 — Cylinder 4 Misfire Detected
Frequently Asked Questions
Can I drive with code P0382?
P0382 is severity 2 — service this week. Not an immediate stop, but ignoring it usually compounds the problem. Most common cause for this code is a worn sensor or minor performance fault that won't strand you today but will get more expensive the longer you wait.
How much does it cost to fix P0382 on a commercial truck?
Total repair cost ranges $100–$900 depending on the root cause. The cheapest fix is usually the first one listed below — One or more glow plugs failing or drawing incorrect current — which is also the most common. On commercial trucks the cost is usually higher than passenger vehicles due to part availability and shop labor rates ($120–185/hour at most truck shops, vs $90–130 at general auto shops). DIY-capable fixes (sensors, hoses, filters) are at the low end; major component replacements (turbo actuator, high-pressure fuel pump, transmission solenoid pack) are at the high end. Always diagnose with a scan tool BEFORE replacing parts — guessing wrong on a $1,500 turbo actuator when the actual issue was a $30 boost hose is a common expensive mistake.
Will P0382 fail a DOT inspection?
P0382 is generally not a direct DOT inspection fail item by itself. Inspectors focus on safety-critical systems (brakes, steering, tires, lights, hours-of-service). However, the check engine light alone can trigger additional inspection scrutiny. Best practice: fix the code and clear it before a planned inspection.
What's the difference between P0382 and related codes?
P0382 is closely related to: P0300 (Random/Multiple Cylinder Misfire Detected), P0301 (Cylinder 1 Misfire Detected), P0302 (Cylinder 2 Misfire Detected), P0303 (Cylinder 3 Misfire Detected). These codes share the same subsystem (cold-start) and often appear together. If you see this code, scan for the full code list — fixing the root cause usually clears multiple companion codes at once. If only P0382 is set without the companions, the issue is more isolated.
How do I prevent P0382 from coming back after a repair?
For P0382 (Glow Plug/Heater Circuit A Range/Performance), prevention centers on the cold start system. Test glow plug system annually before winter. Use a battery in good condition — weak batteries make glow plugs work harder. Park indoors below -10°F if possible.